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A

Absorption: The ability of a surface to absorb sound. The absorption coefficient of a material is a figure between 0 and 1, representing its degree of absorption.
AC: Alternating Current. Electron flow that changes direction alternately.
AC coupled: When a circuit does not pass the DC component of a signal,and it ignores DC offsets.
Achromatic: Completely colorless white light.
Acoustics: The study of sound-wave motion and sound behaviour both within an enclosure and out of doors. Also The qualities of a room in respect to transmission to sound.
Aesthetic: Often applied to theatrical designs or directing styles; in sound, the end product of the sound system and how it evokes mood, enhances the play, etc., etc.
A/D: Analog to Digital converter. A device that converts an analog signal to a digital value. Converts an audio signal in its electrical form into a digital binary data stream
ADA: Analog Distribution Amplifier. A device that takes in one signal and distributes it to several outputs without tying those outputs together (buffered).
Adapter: A linking device that allows two dissimilar devices to connect physically, and/or communicate electronically, such as a VGA to Mac adapter.
ADC: Analog-to-digital converter. A device used to convert analog signals to digital signals.
Additive color process: Also called "RGB." A color generation process used in video that combines red, green, and blue to make all colors. All three colors (red, green, and blue) at 100% combine to make white on a video screen; the absence of all three colors (0%) makes black. Also see Subtractive color process (CYMK). video, aliasing is typically caused by interference between the luma and chroma frequencies or between the chroma and field scanning frequencies. It appears as a moire or herringbone pattern, straight lines that become wavy, or rainbow colors. Also see Cross color. (3) In digital video, insufficient sampling or poor filtering of the signal causes aliasing. Defects typically appear as jagged edges on diagonal lines and twinkling or brightening in picture detail. See Antialiasing.
AES14-1992 (r1998): AES standard for professional audio equipment, application of connectors, part 1, XLR-type polarity and gender [1999-03-05 printing]. Soon XLR connectors with more pins and special purposes were developed. Since the AES standard AES 3-1992 the three-pin XLR connector is also the standard connector for AES/EBU digital connections (electronically balanced, impedance 110 ohms).
AGC (Automatic Gain Control): Automatic gain can be applied ahead of almost any circuit that requires specific levels to operate. As an example, the color decoder needs to see a particular level of color sub-carrier at its input in order to display the correct color at the output. There is a reference burst at the beginning of each horizontal line of known original amplitude. The AGC circuit looks at the incoming signal level and applies any gain correction necessary to make the burst amplitude correct. In the process of doing that, it also corrects the amplitude of the color information in the active picture area.
AM: Amplitude Modulation. A method of radio transmission, by which the information part of the signal causes the amplitude to vary without affecting the frequency. Amplitude modulation is a process used for some radio (AM broadcast) and television video transmission. A low frequency (program) signal modulates (changes) the amplitude of a high frequency RF carrier signal (causing it to deviate from its nominal base amplitude). The original program signal is recovered (demodulated) at the receiver. This system is extensively used in broadcast radio transmission because it is less prone to signal interference and retains most of the original signal quality. See Frequency Modulation.
Ambience: Reverberation and early reflections. The characteristic sound of a location that tells the ear it is listening in a particular room, concert hall, etc.
Ambient Noise: The prevailing sound field in a room in the absence of an applied signal from a loudspeaker, musical instrument, or other sound source.
American Wire Gauge (AWG): A system in the United States for measuring thickness of wire. The lower the number, the larger the diameter of the wire.
American National Standards Institute (ANSI): The American National Standards Institute is the organization that sets standards for US A/V equipment.
Amorphous: (1) Without definite form or shape; not crystallized. (2) An early type of LCD panel technology before polysilicon.
Amp: Ampere. The international base unit of current that represents the rate flow of electric charges through a conductor. Symbolized by "A." 1 amp is equal to the steady current produced by 1 volt applied across a resistance of 1 ohm.
Amplifier: A device used to increase the strength of a signal. An electronic device that takes in an original signal and gives it more power and provides it as an output. Also a device that increases signal level sufficiently to drive a speaker system.
Amplitude: The level or strength of a signal as measured by the height of its waveform. Electronic waveforms can be displayed and measured on an oscilloscope. More amplitude means more sound.
Analog: A continuously varying action, or movement that takes time to change from one position to another. Standard audio and video signals are analog. An analog signal has an infinite number of levels between its highest and lowest value. (Not like digital, where changes are by steps.) Analog representations of sound reproduce the exact waveform, transferring it through different mediums; in a sound system, the microphone (a transducer) creates an electrical analog of the sound pressure waves it hears; the amplifier creates a larger electrical analog of the electrical signal it receives; the speaker creates an acoustic (sound pressure waves) representation of the electrical signal it receives.
Analog control: A method using continuously varying or open and closed circuits voltage levels to provide control of audio and video, lighting and special effect equipment.
Analog recording: A method of recording and encoding information by use of a continuously varying signal, rather than by discrete (digital) pulses.
Anamorphic: A type of lens or adapter designed to produce a wide-screen image from a condensed image on the film. Trademarks are held by CinemaScope, Panavision, and Vistavision.
Anamorphic DVD: A DVD that has a widescreen video image that has been horizontally squeezed. This allows a full widescreen image to be displayed on a 16x9 screen.
Anechoic: Echo free; an anechoic room is a room whose walls, ceiling, and floor are covered with a sound-absorbing material.
Antialiasing: In computer graphics, antialiasing is a technique for smoothing jagged edges by blending shades of color or gray along the edges. Some video devices, such as character generators, have an antialiasing feature to minimize aliasing through filtering and other techniques. See Aliasing.
Aperture: The opening, usually an adjustable iris, which controls the amount of light passing through a lens. In motion picture cameras, the mask opening that defines the area of each frame exposed. In motion picture projectors, the mask opening that defines the area of each frame projected.
Aperture grill: A screen-like feature of Sony Trinitron monitors and others licensed by Sony that controls the number of electrons hitting the phosphor coating on the screen.
APL (Average Picture Level): The video signal level, during the active picture part of each horizontal line, is mathematically averaged over the period of a frame to come up with APL, television program material is said to have a 15% average picture level over a measured period of time
Array: Generic name for a single collection of loudspeakers centrally hung in an auditorium. Also "Cluster."
Artifacts: Artifacts are visible corruption of the image or undesirable elements or defects in a video picture. These may occur naturally in the video process but must be eliminated to produce a high quality picture. The most common reasons for video artifacts are cross color and cross luma.
ASCII: American Standard Code for Information Interchange. The standard code consisting of 7-bit coded characters (8 bits including parity check), used to exchange information between data processing systems, data communication systems, and associated equipment. The ASCII set contains control characters and graphic characters.
Aspect ratio: The relationship of the horizontal dimension to the vertical dimension. In viewing screens, standard TV is 4:3, or 1.33:1; HDTV is 16:9, or 1.78:1. Sometimes the ":1" is implicit, making TV = 1.33 and HDTV = 1.78.
ASTA: Active Sync Termination Adapter. A VGA-style (15-pin HD connector) adapter that provides active circuits that shape up the horizontal and vertical sync signals. This adapter may be used to eliminate jitter and/or intermittent tearing in the displayed image. Most small digital projectors are designed to be near the video source and may not provide impedance matching. See LSTA (Laptop Sync Termination Adapter).
Asynchronous: Intermittent, not synchronized or continuous. A conversational type of communication that allows the parties at each end to talk when they like, instead of at a prescribed time. Used in videoconferencing.
ATM: Asynchronous Transfer Mode. In videoconferencing, a system for transmission and switching of digital signals through the telephone system. See Asynchronous.
ATSC: Advanced Television Systems Committee. The ATSC was formed to establish voluntary technical standards for advanced television systems, including digital high definition television (HDTV). The ATSC is supported by its members, who are subject to certain qualification requirements.
Attack Time: In a compressor or expander, the interval during which the output level moves from its pre-threshold level to whatever gain is dictated by the compression/expansion ratio. Translation: how fast a compressor moves.
Attenuator: Device which reduces the signal flowing through a circuit, commonly found built-in to connectors in values of 10dB from 10dB to 60dB. Translation: takes a very "hot" (loud) signal and makes it softer, so it doesn't overload the circuitry in question. Also "Pad."
Attenuate/Attenuation: To reduce the amplitude (strength) of a signal or current.
Audio: Of or concerning sound, specifically the electrical currents representing a sound program or the sound portion of an A/V program.
Audio dub: To r e-record the audio portion of a videotape without disturbing the video portion. To copy audio from one tape to another.
Audio follow: A term used when audio is tied to other signals, such as video, and they are switched together. The opposite of "breakaway."
Audio Visual Equipment: Product that is used in presentations, meetings and tradeshows to display media of various types
Audio Visual Rentals: A company that provides audio visual equipment to rent or hire for short periods of time, generally without an operator. Mediaco is an audio visual rentals company.
Audio Visual Staging: A company that provides audio visual equipment to rent or hire for short and longer time periods, with personnel to set up, operate and manage the equipment. Mediaco is an Audio Visual Staging company
Audio Video Staging: Similar to an audio visual staging company, this kind of firm generally focuses on special events and larger equipment needs events. Mediaco is an Audio Video Staging company.
Auto-focus: Automatic focus. A device in a projector or camera that uses light reflected from a surface to focus the image.
AUTOMATED FIXTURE: A lighting fixture in which some functions have been electronically or mechanically automated such as: color change, beam movement, shutter, iris, and gobo change, as well as internal dimming capabilities.
AUTOMATED FIXTURE CONTROL CONSOLE: A lighting control console designed specifically for the purpose of controlling and storing/playing back cues for automated fixtures. Complex cue structures, effects, and chases are typical features of automated fixture control consoles.
Automatic convergence: The automatic alignment of the red, green, and blue color images on a screen.
Automatic sync stripping: The automatic removal of sync signals from video channels. Typically, this is associated with removing the sync signal from the green channel, but it may apply to stripping the sync off of all three video channels (Red, Green, and Blue).
Autosequencing: A switcher feature that causes the switcher to automatically select each one of its channels in succession, repeatedly sequencing through all channels.
Autosizing: Automatic picture sizing adjustment to compensate for different display modes, thus enabling the display system to center the picture and fill the screen.
Autoswitching: The feature that enables a product to detect which input has an active sync signal and to switch to that input.
Auto-termination: In equipment that has loop-through or daisy-chain connections, termination is done at the last device on the chain. Some such devices provide termination automatically by having no cable going out, thus indicating that this is the last device and termination is provided.
Auxiliary Return: A specific line-level input on a console designed to receive a signal from an effects processor. Usually stereo.
Auxiliary Send: A specific output bus connected to each channel (with its own level control) that sends a signal out of the mixer; can be used as an additional output (for monitors, recording, whatever).
A/V: Audio visual, or audio video.
AVI: Audio Video Interleaved: The Video for Windows file format for digital video and audio
AWG: American Wire Gauge. A standard measurement for wire conductor diameter.
Axis: An imaginary line that is perpendicular to the front face of the microphone diaphragm. Those sounds reaching the microphone at an angle to the axis are said to be off-axis. Can also be applied to loudspeakers.

B

B-ROLL: Stock footage acquired for miscellaneous needs
BACK FOCUS: A mechanical adjustment in a camera that moves the imaging device plane relative to the lens to compensate for different focal lengths of lenses.
Back porch: The time in a composite video signal that is between the trailing edge of the sync pulse and the trailing edge of the blanking pulse (before the video information). See Blanking.
BACK LIGHT: Illumination from behind the subject and opposite the camera. Provides a depth of field for the cameras subject
Background Music: Appropriate music, enhancing the mood of an event.
Balanced audio: A method that uses three conductors for one audio signal. They are plus (+), minus (-), and ground. The ground conductor is strictly for shielding, and does not carry a signal. Also called "differential audio."
Balanced/Unbalanced: An unbalanced line is one where there are only two signal carrying conductors, one of which is the shield. In the balanced line the shield, which is grounded, is in addition to two conductors. Balanced lines are less prone than unbalanced to interference. In balanced lines, one of the signal wires carries the audio signal, while the other carries an inverted copy. When the signal reaches the destination, the inverted copy is flipped and added to the original. Any noise added by the wire is also inverted. When combined with the non-inverted noise, the two noise signals cancel each other out.
BALLYHOO: A followspot or lighting move in which the operators continuously move the beam in a figure-eight motion around the stage or audience. This term is also used to describe similar movements performed by moving lights
Banding: A video problem of dark bars appearing across the displayed image in areas where there is movement.
Bandwidth: The total range of a frequency required to pass a specific signal without significant distortion or loss of data. In analog terms, the lower and upper frequency limits are defined as the half power, or -3dB signal strength drop compared to the signal strength of the middle frequency, or the maximum signal strength of any frequency, expressed as xx Hz to xx kHz (or MHz) @-3dB. In digital terms, it is the maximum bit rate at specified error rate, expressed in bits per second (bps). A device's bandwidth should be wider than the highest possible bandwidth of the signals it may handle. (In general, the wider the bandwidth, the better the performance. However, too wide bandwidth may pass excessive noise along with the signal.)
BARN DOOR: An adjustable metal flap or group of metal flaps attached to the front of a lamp housing to prevent light from spilling outside a desired area.
BAYONET MOUNT: The most common type of mount used on most cameras to secure the lens on the body by using a rotating lens fixing ring.
Barrel: Outward curved edges on a display image. Also see Pin cushion.
Barrel connector: An adapter used to connect two coax-type connectors of the same gender.
Baseband: A prime signal such as composite video, component video, and audio having its own path and that is not modulated onto a carrier signal or combined with other signals on a path. An un-modulated signal or band of signals. The video signal seen on a waveform monitor is a baseband video signal.
Baud: Named for J. M. E. Baudot, the inventor of the Baudot telegraph code. The number of electrical oscillations per second, called baud rate. Related to, but not the same as, transfer rate in bits per second (bps).
Bend radius: The radius of the arc formed by bending a cable. The most a cable can bend without damage or without adversely affecting its electrical characteristics. The general rule is that the bend radius must be no less than 10 times the outside diameter of the cable jacket. However, it also depends upon the materials that make up the cable.
Bending: A video problem when the top of the screen hooks, bends, or tears to the side. Also known as "hooking."
Betacam: Professional camera/recorder format using a component video system.
Betacam SP: A superior performance version of Betacam using metal particle tape and a wider bandwidth recording system.
Betacam SX: Another format of Betacam. SX and SP are not interchangeable.
BIAS: A direct current (DC) or a high frequency alternating current (AC) signal fed to a magnetic recording head with the audio in order to minimize distortion. AC Bias ordinarily provides higher fidelity.
Bidirectional: When signals can pass in either direction through the same port or by the same path. RS-232 communications are bidirectional because the devices at either end can transmit and receive.
Bi-amping: Process whereby the amplifiers are placed in the sound system after the crossover, one channel for low frequencies, one for high. Produces a cleaner sound than if a single amp had been placed before the crossover; crossover is not subject to high power levels; amplifier channels are dedicated to a certain frequency range whereby it can operate much more linearly, lessening distortion.
Bi-directional microphone: A microphone that is equally sensitive to sounds arriving from the front and back, and insensitive to sounds arriving from the sides. A figure-8 microphone.
Binary: A numbering system using base-2. Each digit is represented by a 1 or a 0 (on or off ).
Binary code: A coding system using the digits 0 and 1 to represent a letter, numeral, or other character in a computer. For example: the character "A" in ASCII code becomes 0100 0001 in binary.
Binaural: Sound reproduction using two microphones usually in a "dummy head" (to emulate the shape and the response of the human hearing system) feeding a pair of headphones, so that the listener hears the sound he or she would have heard at the recording location.
B-ISDN: Broadband Integrated Services Digital Network. A special version of ISDN that uses fiber optics and can transfer at 1.5 megabits per second. Also see Integrated Services Digital Network (ISDN).
Bit: The shortened form of "binary digit" (0 or 1). A bit is the smallest unit of information in a computer.
Bit map: A method of graphic display using rows and columns of dots, or pixels. Each pixel location corresponds to a location in memory.
Black: The darkest visible surface, created by the absorption of all incident light and color. In video, the transmission of horizontal and vertical sync signals without picture information.
Black and white: Monochrome (one color) or luma information. In the color television system, the black and white portion of the picture has to be one color: gray, D6500, 6500K, as defined by x and y values in the 1939 CIE color coordinate system.
Black burst: The video waveform without the video elements. It includes the vertical sync, horizontal sync, and the chroma burst information. Black burst is used to synchronize video equipment to align the video output. One signal is normally used to set up an entire video system or facility. Sometimes it is called House sync.
Black burst generator: A special device for calibrating video equipment by generating a composite video signal with a totally black picture. This black burst signal is used to synchronize video equipment to provide vertical interval switching. It also provides black level and chroma burst information for maintaining uniform video levels and color information.
Black level: More commonly referred to as "brightness," the black level is the level of light produced on a video screen. The level of a picture signal corresponding to the maximum limit of black peaks. The bottom portion of the video wave form, which contains the sync, blanking, and control signals. The black level is set by the brightness control.
Blanking: The interval after the electron beam completes a scan line and returns (retraces) to the left. During this time, the beam must be turned off (horizontal blanking). Similarly, when the last line has been scanned at the bottom of the screen, the beam must return to the upper left (vertical blanking).
Blanking-adjustable: On signal processing products this refers to the ability to adjust the degree of blanking on the image. This is useful for eliminating artifacts (such as closed caption noise that can be seen at the top of an image).
Blanking level: The level of a video signal that separates the picture information from the sync information. The level of the front and back porches is Zero IEEE units. To blank the video signal, the video level is brought down to the blanking level such that nothing is visibly displayed, while the electron beam returns (retraces) to the start of the next line.
Blooming: Most noticeable at the edges of images on a CRT, blooming is when the beam hitting the screen is too intense and overdrives the phosphors. The edges of an image seem to exceed its boundaries. Thin lines and sharp edges may look thick and fuzzy. This may be caused by the contrast being set too high, or by a high voltage problem.
Blue enhancement: Mixes the right amount of blue information with the green signal for displaying text in a more readable aqua color. This color mixing affects all blue colors on the display screen (used only for TTL signals).
BNC: Bayonet Neill-Concelman. A cable connector used extensively in television and named for its inventor. A cylindrical bayonet connector that operates with a twist-locking motion. To make the connection, align the two curved grooves in the collar of the male connector with the two projections on the outside of the female collar, push and twist. This allows the connector to lock into place without the need for tools.
BOOM MICRPHONE: Any microphone, but usually a unidirectional or shotgun microphone, attached to a pole or boom stand to keep the microphone near an audio source but outside of the field of view, or to allow a person playing a musical instrument to get close to the mic without the stand interfering
Boost control: Boost control can compensate for losses of signal level or picture contrast that result from increase in cable resistance as cable length increases.
Boot/Boot-up/Bootstrap: The initialization process a system goes through after power comes on. It may also occur as part of resetting. To start a new beginning, you "pull yourself up by your bootstraps."
Bow: The curving of scan lines in the center of the image.
Box Truss: An aluminum or steel support structure often used for temporary rigging of lights, scenery, or sound equipment.
Breakaway: The ability to separate audio and video signals for switching them independently. For example, the audio and video signals from one source may break away and be switched to two different destinations. This is the opposite of the term "audio follow."
Breezeway: The early part of the back porch portion of the video signal. The area between the horizontal sync pulse and the color burst.
Bridge (or multipoint bridge): A device that allows multiple systems to dial in and participate in a single videoconference.
Bridging: A technique used with an amplifier where there is a single input to both channels and the output from both channels is summed into one: provides for more amplifier power. WARNING: not all amplifiers will perform well when bridged. See owner's manual of amplifier in question for information.
Bridle: A rigging device or method which distributes a single point of a load to more than one hanging point.
Brightness: Usually refers to the amount or intensity of video light produced on a screen without regard to color. Sometimes called "black level."
Brightness control: The control on a television monitor that increases or decreases the radiance of an image.
Brightness ratio: The difference between the lightest (whitest) and darkest (blackest) areas in an image. The wider the brightness ratio, the wider the contrast ratio.
Brightness signal: Same as the luma (Y) signal; a signal that carries information about the light intensity at each point in the image.
Broadband: A communications channel that has greater bandwidth than a voice-grade line and is potentially capable of greater transmission rates.
BROADCAST QUALITY: A term used to describe the output of a manufacturer's product, meaning that the technical specifications meet the minimum FCC rules for broadcasting.
Buffer: Generally referred to as a unity gain amplifier, a buffer is used to isolate the signal source from the load. A buffer can be used for digital or analog signals.
Burn-in: In a video display, this term describes what happens when an image has been displaying too long, resulting in a permanent image being burned into the screen phosphor.
Bus: A path for transporting voltages, signals, or a ground between the different sections of an electronic device, such as a data bus between a CPU and memory or a peripheral device. Its width is determined by the number of lines (conductors) that make up the bus, and its speed (data transfer rate) is determined by the circuits that drive the lines.

C

C-MOUNT LENS: Lenses with a standard one-inch threaded mount assembly that is screwed into the camera body, as opposed to a bayonet or "m" mounts
Cable: Ambiguous term; could refer to heavy-duty electrical cable, light-duty electrical cable, speaker cable, microphone cable, instrument cable, etc. Usually have copper conductors (either stranded or solid) and have some sort of rubber, plastic, etc. insulation.
Cable equalization: The method of altering the frequency response of a video amplifier to compensate for high frequency loss in cables that it feeds. Also see Peaking.
CACHE: A small amount of relatively high speed storage which is used as an intermediary between the data user and a larger, slower storage device (the backing store).
CAD: Computer Aided Design. The use of the computer system for designing, such as in architectural and engineering applications.
Cam-Lok: A connector made by Crouse-Hinds specifically designed to carry large AC mains currents, as in those from a power junction box to a portable dimmer pack or power distribution set-up. One connector per phase, per neutral, and per ground.
CAMCORDER: Combination of camera and video tape recorder in one device.
CAMERA SUPPLY: Most video cameras use an external DC voltage supply which is derived either from a battery belt worn by the camera operator, from a battery within the video recorder itself, or from the mains power supply.
CANNON: A three-pin connector used with balanced audio lines for line and mic level audio signals. Also known as an XL or XLR connector
CAPSTAN: A rotating shaft or spindle which moves tape at a constant speed during recording or playback in tape recorders and players while a pressure roller squeezes or pinches the tape tight against the capstan to provide traction.
Capacitor: An electronic circuit element that stores energy by creating an electrical field between two conductors; at a given parameter, the capacitor will discharge; AC can flow through a capacitor but DC cannot.
Capacitance: The ability to store an electrical charge.separated by insulators and capable of storing an electrical charge. When there is a difference of potential between the conductors, and because current cannot flow through the insulator, an electrical charge is stored.
Captive screw connector: A connector that uses screws that don't fall out when loosened to insert the wires. (Tighten the screws to secure the wires.)
Cardioid Microphone: A unidirectional microphone with 6dB of attenuation at the sides (�90 degrees) and a null at 180 degrees. So called due to the cardioid-like shape of its polar pattern. In a few words, it picks up more sound from the front than from anywhere else.
Cascading: The act of connecting two or more mixers to each other in order to extend the number of inputs available.
CAT 3: ANSI/EIA (American National Standards Institute/Electronic Industries Association) Standard 568 is one of several standards that specify"categories" (the singular is commonly referred to as "CAT") of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain. CAT 3 cable has a maximum throughput of 16 Mbps and is usually utilized for 10BaseT networks.
CAT 5: Category 5. Describes the network cabling standard that consists of four unshielded twisted pairs of copper wire terminated by RJ-45 connectors. CAT 5 cabling supports frequencies up to 100 MHz and speeds up to 100 Mbps. CAT 5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard.
CAT 5e: Enhanced Category 5. The standard for the next higher grade of unshielded twisted pair (UTP) beyond Category 5. The CAT 5e specification has been developed to provide more robust support for 1000Base-T. CAT 5e will specify tighter limits than CAT 5 for NEXT, ELFEXT, and return loss.
CAT 6: Category 6. The proposed standard for 4-pair, 100 ohm Category 6 cabling. The standard defines components (cable and connecting hardware) and cabling (basic link and channel) for Category 6 channels, as well as Level III field tester requirements. CAT 6 supports frequencies up to 250 MHz and speeds up to 250 Mbps.
CAT 7: Proposed and pending standard. Category 7 unshielded twisted pair cable is rated up to 600MHz.
CATV: Acronym for cable TV, derived from the older term, community antenna television
CAV: Component Analog Video. Component video signals in which an analog voltage or current (rather than a set of numbers) represents the value of the pixel, the same as analog components. Encoded video signals can provide greater color resolution than composite video. An NTSC encoder must be used to convert the signals for a standard NTSC receiver.
CAV: Constant Angular Velocity. Constant RPM or revolutions per minute). A laserdisc format.
CCD: Charge Coupled Devices. A light-detecting circuit array used in video cameras, scanners, and digital still cameras. Advantages include good sensitivity in low light and absence of the burn-in and phosphor lag found in CRTs.
CCITT: French term for Consultative Comit� of International Telephone and Telegraph. The international group that sets standards for telephony and digital communications (e.g., H.320-the audio and video codecs and protocol for ISDN).
CCTV: Closed Circuit Television. A distribution system that limits reception of an image to those receivers which are directly connected to the origination point by coaxial cable or microwave link.
CCU (Camera Control Unit): A device separate from a camera head that contains various video controls, including registration, color balance, contrast, and brightness. With the CCU the video operator adjusts the camera picture during the event.
CD-I Compact Disc-Interactive: A format that provides audio, digital data, still graphics and limited motion video.
CD-R (Compact Disc, Recordable): A compact disc that can be written to only once.
CD-ROM Compact Disc-Read Only Memory.: A 4.75 inch laser-encoded optical memory storage medium with the same constant linear velocity (CLV) spiral format as compact audio and some videodisks.
CD-RW (Compact Disc, Rewritable): A compact disc that can be written to, and the subsequently added to, or erased and rewritten with different data.
CE: Conformit� Europ�enne. A label or mark on a product signifying ESD, EMI, and safety compliance with all European Union (EU) directives applicable to that product. Some interpret it to mean European Community or Compliance for Europe.
CEDIA: Custom Electronic Design and Installation Association. CEDIA is an international trade association of companies specializing in the planning and installing electronic systems for the home. This association offers an annual expo. .cedia.org
CENELEC: European Committee for Electro-technical Standardization.
Center Marker: Reference markings that indicate the center of the image on the viewfinder screen.
CGA: Color Graphics Adapter. Introduced in 1983, it was IBM's first product to display both color and graphics. An RCA jack above the 9-pin video output connector provides NTSC video. The signal type is TTL, non-interlaced, with pixel x line resolution of 640 x 200 and a color palette of 4/16. CGA has a horizontal scan frequency of 15.75 kHz and vertical frequency of 60 Hz.
Chain Hoist: A lifting device comprised of an electric motor and gear/chain drive system commonly used to lift portable trusses into place after assembling them close to the ground
Channel Fader: The level control (usually, a slide fader) on a mixer normally found in the channel path.
Channel Strip: The physical representation of an audio channel on the front panel of a mixer; usually a long, vertical strip of controls.
Chip Chart: Black and white test chart, containing "chips" in varying intensities that make up a gray scale used to check the gray scale taking characteristics of a camera, including the gamma parameter
Chroma: (chroma signal) (1) Hue and saturation are qualities of chroma. Chroma does not include black, gray, or white. The purity or intensity of color, sometimes called "hue." Color information, independent of luma intensity or brightness. Without the chroma signal, the video picture would be black and white. (2) The (M) NTSC or (B, D, G, H, I) PAL video signal contains two parts that make up what you see on the screen: the black and white (luma) part, and the color (chroma) part.
Chroma burst: See Color burst.
Chroma crawl: An artifact of encoded video also known as dot crawl or cross-luma. It occurs in the video picture around the edges of highly saturated colors as a continuous series of crawling dots ("dancing ants") and is a result of color information being confused with luma information by the decoder circuits.
Chroma delay: A video problem in which the color of an object or area is shifted slightly to the right of the luma (intensity).
Chroma gain (chroma, color, saturation): In video, the gain of an amplifier as it pertains to the intensity of colors in the active picture.
Chroma key (color key): A film and video process in which the subject is filmed in front of a blue or green background (the key color). For example, a weather reporter stands in front of a blue wall with a camera focused on him or her. The camera's video signal feeds into a chroma keyer, which detects the blue background and replaces it with a video signal from another source, such as video of a weather map. Thus, the reporter appears to be standing in front of the weather map. However, the reporter must take care not to wear colors that are similar to the background color or else the image will appear on the reporter.
Chrominance: See Chroma.
CIE: Commission Internationale de l'Eclairage (the International Commission on Illumination). The organization responsible for the chroma diagram of 1939, a three dimensional diagram that defines light and color. Other systems have been developed by CIE more recently.
Clearcom: Communications headsets featuring a mic and an ear muff, that allow the operators of a show to talk to one another discreetly during a show, may be wired or wireless
Client: A computer or network device that uses information supplied by a server.
Cliff effect: The sudden or discrete loss of signal at a digital receiver due to the degradation of a transmitted signal which has been terminated due to an error rate being reached and the received signal being rejected.
Clipping: Distortion at an input or at a mixer or amplifier due to severe overloading. Clipping when using digital equipment (an A/D converter, somewhere) results in static-like noises as the A/D converter doesn't really know what to do with levels over its operation parameters.
Clipping Audio: Term used to describe the result of an amplifier (small or large) running into power supply limitation in that the maximum output voltage that any amplifier can produce is limited by its power supply. Attempting to output a voltage (or current) level that exceeds the power supply results in a flat topping effect on the signal, resulting in extreme harmonic distortion or crackling.
Clipping Video: The electronic process of shearing off the peaks of either the white or black excursions of a video signal for limiting purposes.
Clipping level: An electronic limit to avoid overdriving an audio or video signal.
Closed loop: A continuous loop of film or tape for repetitive playing often enclosed in a cartridge.
Cluster: Generic name for a single collection of loudspeakers centrally hung in an auditorium. Also "Array."
CMR: Common Mode Rejection. A measure of how well a differential amplifier rejects a signal that appears simultaneously and in phase at both input terminals. As a specification CMR is expressed as a dB ratio at a given frequency.
CMRR: Common Mode Rejection Ratio. (1) For a differential amplifier, the ratio of the differential gain to the common mode gain. (2) Expressed in dB it is the ratio of common mode input voltage to output voltage. (3) For an operational amplifier, the ratio of the change in input offset voltage to the change in common mode voltage.
CMYK: Cyan, Magenta, Yellow, and Black. See Subtractive color.
Coaxial cable: A two-conductor wire in which one conductor completely wraps the other, with the two separated by insulation. Constant impedance transmission cable. Example: 75 ohm, type RG-59u cable used for video signals. Abbreviated as coax.
Codec: (1) Coder/decoder. A device that converts analog video and audio signals into a digital format for transmission over telecommunications facilities and also converts received digital signals back into analog format. It may also dial up the connection. (like a modem for teleconferencing.) (2) Compressor/decompressor. Codecs can be implemented in software, hardware, or a combination of both. Some popular codecs for computer video include MPEG, Indeo, Cinepak, QuickTime, and Video for Windows.
Collision: When signals from two or more connected devices on a network attempting to transfer simultaneously crash into each other. Common on Ethernet systems.
Color adjustment: A video adjustment that is used to control color or chroma intensity.
Color bar: SMPTE standard test bars used to match playback with original recording levels as a reference for color intensity, brightness, contrast, and balance. Generated electronically, often accompanied by a 1000 Hz audio tone. A test pattern containing six basic colors-yellow, cyan, green, magenta, red, and blue-used to check the chroma functions of color TV systems.
Color burst: In color TV systems, a burst of subcarrier frequency located on the back porch of the composite video signal. This serves as a color synchronizing signal to establish a frequency and phase reference for the chroma signal. Color burst for NTSC is 3.58 MHz and PAL is 4.43 MHz.
Color encoder: A device that combines the separate red, green, and blue signals into one composite video signal.
Color phase: The timing relationship of the color video signal. The correct color phase will produce the correct color hues.
Coloration: Term used to indicate audible alterations to the sound arising from the response pattern of a mic or loudspeaker; also used to indicate alterations to the sound arising from the environment in question.
Colorplexer: See Color encoder.
Color resolution: The number of colors available at one time in an image, measured in terms of bits per pixel.
Color space: A model of the color spectrum with the ordering of colors by three parameters in a defined 3D space: intensity, saturation, and hue. There are several color spaces with each used to support the specific identity of colors within a structured identification system. In television and video, the CIE 1931 or 1976 color space is most often used.
Color subcarrier: The carrier frequency that contains the color signal information. A 3.58 MHz signal interwoven with a standard NTSC monochrome signal that contains color information.
Color temperature: The color quality, expressed in degrees Kelvin (K), of a light source. The higher the color temperature, the bluer the light. The lower the temperature, the redder the light.
Comb filter: A filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response that resembles the teeth of a comb. This is an improvement over the notch filter. Its precise separation of the chroma and luma reduces both cross chroma and cross luma artifacts (chroma crawl or zipper artifacts). It preserves more detail in the black-and white, resulting in a better quality picture. Although comb filters are successful in reducing artifacts, they may also cause a certain amount of loss of resolution in the picture.
Combing: An undesirable blurring of an image that contains motion. This effect occurs when a single frame of video combines two fields of video derived from different frames of film.
Communication protocol: A specific software based protocol or language for linking several devices together, such as computers and VCRs or edit controllers, for example RS-232
Component digital: See Digital component video.
Component video: Color television systems start with three channels of information: red, green, and blue (RGB). In the process of translating these channels to a single composite video signal, they are often first converted to Y, R-Y, and B-Y. Both 3-channel systems, RGB and Y, R-Y, B-Y, are component video signals. They are the components that eventually make up the composite video signal. Higher quality program production is possible if the elements are assembled in the component domain.
Composite digital: See Digital composite video.
Composite sync: A signal combining horizontal and vertical sync pulses and equalizing pulses with no picture information and no signal reference level. Composite sync is sometimes referred to as "C", "S" (as in RGBS), or "HV" (as on some connector panels).
Composite video: An all-in-one video signal comprised of the luma (black and white), chroma (color), blanking pulses, sync pulses, and color burst. Composite video (also called FBAS) is the standard that connects almost all consumer video equipment; television sets, laser disc players, VCRs and camcorders. Composite video combines the three basic elements of a video picture (color, brightness, and synchronization data) into a single combined composite signal. Usually composite video is transmitted over 75 ohm cables. Long video cables are prone to signal loss and RF interference. The 75 ohm cable chain must be terminated at the ends
Compressor: A variable-gain amplifier in which the dynamic range of the output signal is less than that of the input signal. The compression range may vary from 1:1 to 10:1. Translation: it takes a signal with a large dynamic range, keeps the soft sounds soft, but compresses the louder sounds above a certain threshold. It trims the dynamic range.
Compression artifacts: Compacting of a digital signal, particularly when a high compression ratio is used, may result in small errors when the signal is decompressed. These errors are known as artifacts, or unwanted defects. The artifacts may resemble noise (or edge busyness) or may cause parts of the picture, particularly fast moving portions, to be displayed with the movement distorted or missing.
Computer-video interface: A device that converts the nonstandard video output of computer systems to a standard RGB analog signal, which can then be connected to a compatible data monitor or projector.
Condensation: Moisture condensation usually on the head drum, which cases the tape to stick to the drum, resulting in damaging the tape and possible malfunction of the recorder
Connector: The terminating point of a cable. It enables cables to be connected together.
Console: The central system to which multiple input signals are routed for level control and signal processing, and for combination with other input signals and subsequent routing to a tape recorder, broadcast transmitter, or sound reinforcement system. See mixer.
Constant Directivity: Typically, a loudspeaker in which the produced sound does not become more directional as the frequency rises.
Constant Voltage System: A speaker distribution system commonly used in large installations such as airports, department stores, and schools where a single amplifier is driven at its maximum output voltage (70.7V in North America), and transformers are used at each speaker to control volume level. Using this high-voltage and high-impedance system allows for cable to be small in diameter. However, the sound quality is sacrificed because in order to reproduce the entire frequency spectrum well, the transformers need to be very heavy and very expensive.
Contact closure: The momentary connection of two conductors to complete an electrical circuit. Often used to switch inputs on switchers.
Continuity: In digital picture manipulators, the characteristic of location/positioning that determines whether the motion path continues smoothly, without interruption.
Continuous presence: A feature in some videoconferencing that allows the participants to view multiple sites on the same video screen. This is a function of the codec used and not of the video switching system.
Contouring: Digital video picture defect caused by quantizing at too coarse a level.
Contrast: The range of light and dark values in a picture, or the ratio between the maximum and the minimum brightness values. Low contrast is shown mainly as shades of gray, while high contrast is shown as blacks and whites with very little gray. It is also the name of a TV monitor adjustment, which increases or decreases the level of contrast of a displayed picture. Also called "white level."
Contrast range: The range of grays in a video image.
Contrast ratio: This is the ratio of the high light output level divided by the low light output level. In theory, the contrast ratio of the television system should be at least 100:1, if not 300:1. In reality, there are several limitations. In the CRT, light from adjacent elements contaminates the area of each element. Room ambient light will contaminate the light emitted from the CRT. Well-controlled viewing conditions should yield a practical contrast ratio of 30:1 to 50:1.
Control Track: The magnetized portion along the length of a videotape on which sync control information is placed to tell the VTR how fast to playback the media.
Convergence: The alignment of the red, green, and blue video projected onto a screen when the lines produced by the three color sources appear to form one clearly focused white line. The point at which the light from each of the three lenses aligns so that the perceived single image is clearly focused. Lack of convergence is a video problem when the displayed image appears to be outlined by red, green, or blue because of misalignment of the colors.
Coverage Angle: The included angle between the points on either side of a loudspeaker axis at which the response is attenuated by 6dB with respect to the on-axis level.
COOKIE: The most common meaning of "cookie" on the internet refers to a piece of information sent by a Web Server to a Web Browser that the Browser software is expected to save and to send back to the server whenever the browser makes additional requests from the server. Depending on the type of Cookie used, and the Browser's settings, the Browser may accept or not accept the Cookie, and may save the cookie for either a short time or a long time. Cookies might contain information such as login or registration information, online "shopping cart" information, user preferences, etc. When a server receives a request from a browser that includes a Cookie, the server is able to use the information stored in the Cookie. For example, the server might customize what is sent back to the user, or keep a log of a particular user's requests. Cookies DO NOT read your hard drive and send your life story to the CIA, but they can be used to gather more information about a user than would be possible without them.
Cracked Oil Fog Machine: A simple type of fog machine which atomizes oil into a fine atmosphere, usually by introducing compressed air into a reservoir containing mineral oil. Crackers are also available which crack water into a very fine mist. This type of fog machine can be very harmful to video projectors and their display panels and optics.
Cross color: Moir� or rainbow artifacts in an encoded video picture caused when the video encoder or decoder misinterprets luma detail as color information, resulting in color being displayed where it shouldn't be. It is especially noticeable when the subject wears pinstriped clothing.
Crossfade: The audio equivalent of a video dissolve where one sound track is gradually faded out while a second sound track simultaneously replaces the original one
Crosshatch: A test pattern consisting of vertical and horizontal lines used for converging a color display device.
Cross luma: Dot crawl, chroma crawl. A video artifact that occurs when a composite video decoder incorrectly interprets chroma information (color) to be high-frequency luma information (brightness). This may appear as tiny, colored dots that creep along the edges of objects.
Crossover: Device which separates parts of the audio signal, typically the high frequencies and the low frequencies; crossovers that appear after the amplifier (they are placed inside the speaker (used inside full-range speaker systems)) are called 'passive,' those which are placed before the amplifiers (in bi; or tri-amplification) are called 'active.' Crossovers are, essentially, a high-pass filter and a low-pass filter in parallel; see handy Intro Electrical Engineering book for more info.
Crossover frequency: In a crossover network, the frequency at which the outputs of two adjacent filter networks are both attenuated by 3dB.
Crosstalk: This is caused by interference between two signals, usually from an adjacent channel, which adds an undesired signal to the desired signal. Crosstalk is caused by magnetic induction or capacitative coupling, and can occur when there are grounding problems or improper cable shielding. Video symptoms include noise and ghosting, while audio symptoms include signal leakage.
CRT: Cathode Ray Tube. A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heated cathode and grids in the neck of the tube, making up the gun. Electrons are accelerated from the gun toward the front surface of the tube (screen), producing a beam. The surface on the back of the screen is coated with phosphors that light up when struck by the electron beam. The CRT in a TV is known as the picture tube. Some CRTs have three guns-for red, green, and blue colors.
CTS: Certified Technology Specialist. An A/V and video professional who, through practical experience and extensive industry training programs offered by Infocomm, has developed a high level of expertise.
Current: The flow of electricity, and the rate at which it flows. See Amp.
Cue: A point in a live show when a signal is given for some action, effect or series of effects to take place
Cue Monitors: A small speaker or a pair of headphones used by the operator specifically for cueing microphones, instruments, or recorded media before raising the level to the house sound system.
Cut: An instantaneous transition between two sources. An instantaneous scene change.

D

D1 component: A parallel digital recording format that handles digital component video with a 4:2:2 sampling of Y, Cr, and Cb.
DA: Distribution amplifier. A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors.
D/A: Digital to Analog.
DAC: Digital to Analog Converter.
Damping: Loss of energy in a vibrating system, usually through friction of some sort.
DAT: Digital Audio Tape. A method developed by Sony and Hewlett-Packard for recording large amounts of information in digital form on a small cassette tape.
Data: (1) A representation of facts, concepts, or instructions in a format suitable for communication, interpretation, or processing by human or automated means. (2) Any representations, such as characters or analog quantities, which have meaning.
dB (Decibel in Electronics): The standard unit used to express gain or loss of power. It indicates the logarithmic ratio of output power divided by input power. A power loss of 3dB is an attenuation of half of the original value. The term "3dB down" is used to describe the half power point. In audio work, 0dB is the threshold of hearing. 120dB level is the threshold of pain. A change of 3dB halves or doubles the apparent loudness.
dB (Decibel in Audio): One dB is the smallest change in loudness that the average human ear can detect. 0dB is the threshold of human hearing. The threshold of pain is between 120 and 130dB. The decibel is a ratio, not an absolute number, and is used to identify the relationship between true power, voltage, and sound pressure levels. Decibels alone have no specific meaning. For example, dBV is a voltage ratio; 0dB = 0.775 V root mean square (RMS). dBSPL is the sound-pressure level ratio. It measures acoustic pressure. dBM is a power ratio. dBA takes into account the unequal sensitivity of the ear, and sound-pressure level is measured through a circuit that compensates for this equal loudness. These measurements are termed A weighted.
dBm: dB referenced to RMS power. 0dBm is a power reference point equal to 1 milliwatt. To convert into an equivalent voltage level, the impedence must be specified. For example, 0dBm into 600 ohms gives an equivalent voltage level of 0.775V, or 0dBu; however, 0dBm into 50 ohms, for instance yields an equivalent voltage of 0.24 V something quite different. Since modern audio engineering is concerned with voltage levels, as opposed to power levels in the early years of telephone, the convention of using a reference level of 0dBm is academic. But in the A/V industry, many people still refer 0.775Vrms as 0dBm, which should be more accurately called 0dBu.
DBS: Direct Broadcast Satellite. A satellite distribution system whereby signals are transmitted directly from an operational satellite to standard receivers. It is the most effective distribution system for remote areas, though transmission may be affected by weather.
dBu: dB unterminated. 0dBu is a voltage reference point equal to 0.775Vrms. [This reference originally was labeled dBv (lower case) but was too often confused with dBV (upper case), so it was changed to dBu (for unterminated)] +4dBu is a standard pro audio voltage reference level equal to 1.23 Vrms. XLR and captive screw audio connectors are commonly used in this equipment.
dBV: dB referenced to RMS voltage. 0dBV is a voltage reference point equal to 1.0 Vrms. -10dBV is a standard audio line level for consumer and some pro audio use, equal to 0.316 Vrms. RCA audio connectors are a good indicator of units operating at -10dBV levels.
DC: Direct Current. The flow of electrons in one direction.See Direct Current
DC coupled: A circuit that passes both AC and DC components of a signal, and therefore is sensitive to DC offsets.
D connector: A connector with rounded corners and angled ends, taking on the shape of the letter D. Commonly used in computers and video, most D connectors have two rows of pins. If they have more than two rows, they are usually called HD (High Density) connectors.
DC offset: A DC voltage level combined with an AC signal.
DC restoration: The correct blanking level for a video signal is zero volts. When a video signal is AC-coupled between stages, it loses its DC reference. A DC restoration circuit clamps the blanking at a fixed level. If set properly, this level is zero volts.
DDC: Display Data Channel. A bidirectional communications standard developed by VESA (Video Electronics Standards Association) that defines a universal data transmission standard for the connectivity between display devices and computers.
DDSP�-Digital Display Sync Processing�: A signal handling method that allows the sync signal to pass through without altering sync pulse timing or width. DDSP disables other sync processing features such as horizontal and vertical centering.
DDWG: Digital Display Working Group. The DDWG develops standards for digital displays. Developer of the DVI standard.
Dead Hang: A rigging term that means the item in question is hung straight off of the point, rather than using a motor or chain-fall.
Decoder: (1) A device used to separate the RGBS (red, green, blue, and sync) signals from a composite video signal. Also called an NTSC decoder. (2) The device in a synchronizer or programmer that reads the encoded signal and turns it into some form of control.
Default gateway: The routing device used to forward all traffic that is not addressed to a station within the local subnet.
Definition: The fidelity with which a video picture is reproduced. The clearer the picture, the higher the definition. Definition is influenced by resolution.
Degausser: A device that produces a strong alternating electromagnetic field which quickly erases an entire reel, cassette, or cartridge of tape. Also used for eliminating ghosting in television monitors by demagnetizing the CRT.
De-interlacing: The process of combining pairs of interlaced fields of video into one progressive frame of video.
Detail: An adjustment that enhances/improves image sharpness.
DFP: Digital Flat Panel. A digital video connectivity standard that was developed by VESA (Video Electronics Standards Association). This is a 20-pin connection standard that handles only digital video signals. This standard uses TMDS (Transition Minimized Differential Signaling) from Silicon Image and DDC (Display Data Channel), also from VESA (Video Electronics Standards Association).
DHCP: Dynamic Host Configuration Protocol. A protocol that lets network administrators manage centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network. Using the Standard Internet protocol (TCP/IP), each machine that connects to the Internet needs a unique IP address. When an organization sets up its computer users with a connection to the Internet, an IP address must be assigned to each machine. Without DHCP, the IP address must be entered manually at each computer and, if computers move to another location in another part of the network, a new IP address must be entered. DHCP lets a network administrator supervise and distribute IP addresses from a central point and automatically sends a new IP address when a computer is plugged into a different place in the network. DHCP uses the concept of a "lease" or amount of time that a given IP address will be valid for a computer. The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. It is especially useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconfigure networks in which there are more computers than there are available IP addresses. DHCP supports static addresses for computers containing Web servers that need a permanent IP address.
DI Box (Direct Input): A device that enables a musical instrument (guitar, etc.) to be connected directly to a mic or line-level mixer input as the box provides the high input impedance required by the instrument and puts out the correct level for the mixer.
Diaphragm: The moving element of a microphone that converts sound-wave energy into mechanical energy.
Dichroic: A type of mirror, reflector, or filter which selectively reflects different wavelengths of light, permitting a projector to transmit more visible light with less heating of the film. Dichroic mirrors are also used for internal convergence of 3-tube single lens video or computer projectors.
Differential audio: See Balanced audio.
Differential gain: Unwanted variations in a chrominance subcarrier's amplitude that result from changes in the signal's DC level, usually specified in degrees over a frequency range.
Differential phase: Unwanted variations in a subcarrier's phase as a result of changes in the chrominance signal's DC level, usually specified between 10% and 90% of full scale.
Diffraction: The manner in which sound can bend around obstacles.
Digital: A system of data or image values in the form of discrete, non-continuous codes, such as binary. When data is in a digital format, it can be processed, stored (recorded), and reproduced easily while maintaining its original integrity.
Digital component video: (1) Digital video using separate color components, such as Y'CbCr or R'G'B'. See CCIR 601. It is sometimes incorrectly referred to as D-1. (2) A digital representation of a component analog signal set, most often Y, B-Y, R-Y. The encoding parameters are specified by ITU-R BT.601-2 (CCIR 601). The parallel interface is specified by ITU-R BT.656 (CCIR 656) and SMPTE 125M.
Digital composite video: (1) Digital video that is essentially the digitized waveform of (M) NTSC or (B, D, G, H, I) PAL video signals, with specific digital values assigned to the sync, blank, and white levels. It is sometimes incorrectly referred to as D-2 or D-3. (2) A digitally encoded video signal, such as NTSC or PAL video, that includes horizontal and vertical synchronizing information.
Digital Light Processor (DLP): A DLP is a semiconductor light switch controlling 480,000 digitally controlled and individually activated mirrors on a single microchip, creating high definition, high contrast images with absolute picture uniformity and full color saturation from middle to all edges
Digital control: A method using discrete digital impulses to control individual functions within a system.
Digital signal: Digital signals, such as TTL signals, have only two levels: high/low or on/off.
Digitization: The transformation of an analog signal into digital information.
Digitizers: Video digitizers utilize video cameras to take pictures of photographs or live and still action. The information is decoded into RGB (digital form) and stored in the frame buffer.
D-ILA � -Direct Drive Image Light Amplifier: Developed by Hughes-JVC, D-ILA uses digitally addressed ILA� instead of CRT-addressed as with earlier devices. (See ILA.) The D-ILA is a device based on the Image Light Amplifier or ILA developed by Hughes-JVC Technology Corporation. The D-ILA technology is a reflective liquid crystal modulator where electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in Integrated Circuit technology.
Dimmer Land: A colloquialism for the area at an event, usually close to the primary power feed, where the dimmer racks are set up.
Dimmer Rack: Dimmer racks contain individual dimmer modules arranged for electrical connection containing 6, 12, 24, or 48 dimmer modules typically with 2 dimmers per module.
DIN connector: An acronym for Deutsche Industrie Norm. A round connector with notches, or keys for alignment. They can be in several sizes: 4-pins, 5-pins, 8-pins, etc. A convenient way of combining all of the signal lines in one connector, 4-pin DIN connectors are often used for S-video.
Diode: An electronic device that allows current to flow in one direction only.
DIP: Dual In-line Package A universal method of manufacturing integrated circuits (ICs) with the pins arranged in two parallel rows. Some DIP components are soldered in and some use DIP sockets.
DIP switches: Small switches that are used to change settings on printers, computers, interfaces, switchers, modems, etc. They are designed to fit in a DIP space on a circuit board.
Direct Box: A small interface box used to take an unbalanced, high-impedance output of a guitar, guitar amp, bass, bass guitar amp, etc, and convert it to a balanced, low-impedance mic-level output for input at the mixer.
Direct Current: Electric current that flows in one direction only, as opposed to alternating current.
Direct Injection (DI): Process whereby a signal is taken from a keyboard or guitar, etc, direct (via a connector box (the Direct Box)) to the mixer. Used instead of a microphone.
Display adapter: A circuit board added to a computer to drive a monitor or other display device.
Display device: Any output device for presenting information visually. Examples include: CRT (Cathode Ray Tube), LED (Light Emitting Diode), LCD panel (Liquid Crystal Display), or gas plasma. A general term for a projector or monitor.
Dissolve: (1) An effect in which one scene or picture fades out as another fades in. In projection, the dissolve effect is achieved by varying the intensity of the lamps in the two projectors involved. Sometimes called lap dissolve or cross fade. (2) The hardware controlling the dissolve effect, which is properly called dissolve control or dissolve unit. A visual effect wherein one scene gradually fades away while slowly being replaced by another. See Fade, Fade-to-black.
Distortion: In Electronics: a measure of the difference between the output and input signals in an amplifier. In Sound Systems: A distortion of a signal that results in dirty sound. Common sources of distortion are in guitar amplifiers (on purpose), and doing such things as plugging a line-level into a mic-level input (overloading the microphone preamp). Basically, you overload something. This occurs due to Harmonic Distortion See "Clipping." In Acoustics: An undesired change in a waveform. Also see "Intermodulation Distortion".
Dither: The method used in digital systems to smooth out the transitions from one bit rate to a lower one. dither makes a digital recording sound and behave more like analog
Diversity: A wireless microphone system that employs two antenna positions per mic; the system hunts for the strongest signal and 'locks on' to it. For further explanation, see Wireless Microphones.
DLP: Digital Light Processing� . See Digital Light Processor
DMD: Digital Micromirror Device. In 1977, it was originally called Deformable Mirror Device. Texas Instruments developed DMD microchips used in DLP (Digital Light Processing) projector subsystems to replace CRT technology. DMD chips use an array of mirrors and memory cells. A digital image is stored in the memory, and then projected when light is reflected onto the mirrors.
DMM: Digital Multimeter.
DMX (Digital Multiplex): DMX is a standard dimmer control protocol implemented to provide a means for interfacing dimming and controlling up to 512 dimmers serially down two wires. DMX can also control equipment from different manufacturers, such as fog machines, strobe lights, and automated fixtures.
DNS: Domain Name System. DNS is the way that an Internet domain name is located and translated into Internet Protocol (IP) addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.
DOC: Declaration of Conformity. A document which states the European Union directives and standards to which particular equipment complies.
DOLBY: A compression/expansion noise reduction system developed and patented by Ray Dolby, widely used in consumer, professional and broadcast audio applications.
Dolly: A wheeled device attached to a tripod to allow smooth movement of a camera
Domain: When referring to the Internet, a name that identifies a network. (i.e. yahoo.com, google.com, msn.com, aol.com)
Doppler Effect: The shift in apparent frequency when the source or the observer is in motion.
Dot clock: Also referred to as pixel clock. The timing device in a graphics card that determines the pixel resolution. The dot clock runs at a rate that produces the highest possible pixel resolution for that device. In a digital projector, the dot clock samples the analog video at a rate that produces the resultant pixel resolution. See Pixel clock.
Dot crawl: Sometimes called "zipper effect," dot crawl refers to a specific image artifact that is a result of the composite video system. Dot crawl may be seen on TV news, for example, when a picture appears over the anchorperson's shoulder, or when some text appears on top of the video clip. If you look closely, along the edges of the picture, or the text that has been overlaid, you'll notice some jaggies rolling up or down.
Dot pitch: The vertical distance (measured in millimeters) between the centers of like-colored phosphors which are in adjacent pixels on the monitor screen. The closer the spacing, the better the resolution. Dot pitch is specified in pixels/mm.
Drop Frame Method: SMPTE time code runs at 30 frames/second, while the NTSC color television system runs at about 29.97 fps resulting in 1 hour as indicated by time code is longer than the actual clock time of 1 hour by 108 frames, or about 3.6 seconds. Drop frame mode adjusts the running of time code by dropping two frames from time code account at the beginning of each minute except every tenth minute
Dropout: A momentary partial or complete loss of picture and/or sound caused by such things as dust, dirt on the videotape or heads, crumpled videotape or flaws in the oxide layer of magnetic tape.
Dry Ice Fogger: A simple fog machine which creates thick, opaque, low-lying or ground fog by the emersion of frozen CO2 in hot water.
Dry contact closure: A pair of electrical contacts that carry no live voltage.
DSK (Downstream Keying): An effect available in some special effects generators in which one video signal is keyed on top of another video signal.
DSL (Digital Subscriber Line): A method of moving data over regular phone lines. A DSL circuit is much faster than a regular phone connection, and the wires coming into the subscribers premises are the same (copper) wires used for regular phone service. A DSL circuit must be configured to connect two specific locations. A commonly discussed configuration of DSL allows downloads at speeds of up to 1.5 M Bit per second, and uploads at speeds of 128 kilobits per second. This configuration is known as ADSL (Asymmetric Digital Subscriber Line). DSL is currently a popular alternative to ISDN, being faster than ISDN and less costly.
DSS: Digital Satellite System.
DTV: Digital Television. Often used to describe one of the many new forms of digital terrestrial transmission of video program material.
Dub: A duplicate copy made from one recording medium to another
DV: Digital Video. A serial digital video format. DV has the advantage over standard analog video of maintaining clear, crisp video without degradation from generation to generation.
DVD: Digital Versatile Disc. An optical disc about the size of a CD-ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video. Originally called digital video disk.
DVI: Digital Visual Interface. The digital video connectivity standard that was developed by DDWG (Digital Display Work Group). This connection standard offers two different connectors: one with 24 pins that handles digital video signals only, and one with 29 pins that handles both digital and analog video. This standard uses TDMS (Transition Minimized Differential Signal) from Silicon Image and DDC (Display Data Channel) from VESA (Video Electronics Standards Association).
DVI/DFP: Digital Video Interface/Digital Flat Panel. The digital video interface computer standard which allows a direct digital video connection between a computer and a digital display.
DVI-D: DVI connector which supports digital signals only.
DVI-I: DVI connector which supports both digital and analog signals.
Dynamic IP address: An IP address that is automatically assigned to a client station in a TCP/IP network, typically by a DHCP server. Network devices that serve multiple users, such as servers and printers, are usually assigned static IP addresses.
Dynamic Microphone: Any microphone whose output is a function of magnetic induction in a voice coil, ribbon, or other conductor moving within a permanent magnetic field.
Dynamic Range: The difference, in dB, between the lowest and highest a system or device is capable of handling.

E

ECL: Emitter Coupled Logic. A family of high speed, low power IC logic devices. Also called "current mode logic."
EDID: Extended Display Identification Data. A communications protocol or instruction set developed by VESA (Video Electronics Standards Association) for the identification of display devices to computers using the DDC (Display Data Channel) transmission standard.
EDTV: Enhanced Definition Television. A complete product/system with the following attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 480 progressive (480p) or higher; no aspect ratio specified; and receives and reproduces, and/or outputs Dolby Digital audio.
EDTV Monitor: Enhanced Definition Television Monitor. DTV minus ATSC tuner and Dolby Digital audio.
EDL (Edit Decision List): A list of a video production's edit points the EDL is a record of all original videotape scene location time references, corresponding to a production's transition events.
EEPROM: Electrically Erasable Programmable Read-Only Memory. The information in an EEPROM is erased by exposing it to an electrical charge. Similar to EPROM except in the way in which information is erased. See Flash memory.
EFP (Electronic Field Production): Production of a television program or program segment by using portable video cameras, VTRs, and sound equipment outside the studios.
EGA: Enhanced Graphics Adapter. Introduced by IBM in 1984, this replaced CGA (Color Graphics Adapter).
EIA-RS-170: The standard broadcast sync as determined by the Electronics Industries Association. Commonly called EIA sync.
EIA: Electronics Industries Association. The association that determines recommended audio and video standards in the US.
EIA sync: The standard broadcast sync, also called EIA-RS-170.
Electron gun: The part in the CRT that produces the electron beam that is attracted to the phosphor-coated back surface of the screen. The beam strikes the phosphors, causing them to emit red, green, or blue light, creating images on the screen.
Electrostatic focus: Also referred to as electrostatic deflection. A CRT tube focusing method that uses electrically charged plates instead of deflection coils to focus the electron beam. This method was used only on small CRTs because the larger the CRT, the higher the voltage required, which can cause harmful x-rays to be emitted.
ELFEXT: Equal Level Far End Crosstalk. The amount of crosstalk at the far end after compensation for attenuation over a run.
EMI: Electromagnetic Interference. Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment. A type of interference caused by mains current flowing through wires in close proximity to audio cables. The magnetic field around the power cables makes its way into the audio cables, causing interference and hum, buzz, etc. Also caused by fluorescent lights, neon lights, switching loads (HVAC equipment), computers, RF transmitters, car ignitions, etc.
Encoder (video): A device, often built into video cameras, that changes individual component signals into composite signals. For example, an encoder combines Y (luma) and C (chroma) signals to produce a video image.
Encoding: Converting to a code. In video, the combination of electronic elements into one signal.
Encryption: To manipulate information into a coded form that cannot be read without a device that will unscramble the code. Video signals are also scrambled in cable and pay-TV systems so that the viewer must pay to receive the program after it has been electronically deciphered.
ENG (Electronic News Gathering): The use of portable cameras, VTR, lights, and sound equipment for the production of a news program or post production.
Enhancing: Improving a video image by boosting the high frequency content lost during recording.
Envelope: Time variation of the amplitude of a vibration.
EPROM: Erasable Programmable Read Only Memory. A device that can store information (instructions or data) and retain it when power is removed. An EPROM is erased by exposing it to ultraviolet light. New information is loaded into the EPROM using a PROM programmer or "burner." See Flash memory.
EQ: Equalization. Selective amplification (signal restoration) applied to a signal in order to compensate for high frequency attenuation and other distortions encountered in long lengths of cable.
Equalizer: The signal processing device used to modify the frequency response of an audio signal. So called because the first such devices were used to correct, or "equalize," the losses in a transmission line.
Equalizing pulses: These pulses cause the vertical deflection to start at the same time in each interval. They also keep the horizontal sweep circuits in step during the portions of the vertical-blanking interval immediately preceding and following the vertical sync pulse.
Ethernet: IEEE standard network protocol that specifies how data is placed on and retrieved from a common transmission medium. Ethernet has a transfer rate of 10 Mbps. It forms the underlying transport vehicle used by several upper-level protocols, including TCP/IP and XNS.
EVC: Enhanced Video Connector. A VESA standard, 35-pin video graphics card connector that can carry signals for video, audio, 1394 (FireWire) and USB (Universal Serial Bus). This allows the computer monitor to act as a central connection hub.
Expansion slots: Slots inside a cabinet that are used to connect additional circuit modules (cards).

F

F-Stop: The size of the aperture in a lens, given in f-numbers. The lower the f-number, the more light passes through the lens. It is the ratio of the lens focal length to the actual diameter of the aperture opening.
Fade, Fade-to-black: A gradual dissolve to another picture, often an allblack screen.
Fader: The master loudness control (usually a fader; sometimes a knob) to the main outputs for each channel on a console. Do not confuse with "gain."
FAQ: Frequently Asked Questions. A list of responses in a Web site or other publication to people's questions.
Farad: Unit of measurement for capacitance. More commonly: picofarads.
Far end: In videoconferencing, the party or group you are connecting to at the distant site.
FCC: Federal Communications Commission. The US governmental agency which controls and makes all policy for the use of broadcast airwaves.
F connector: A type of plug used for RF video connections, such as those used with TV antennas and cable TV to TV sets and VCRs.
FED: Field Emission Display.
Feedback: The high-pitched squeal or ringing caused by sound finding its way out of the loudspeaker back to the mic and out of the speakers again at a resonant frequency dictated by the characteristics of the environment, system, and equipment. It can be lessened by lowering the volume and/or evening out the peaks in the frequency response of the system. Directional mics and speakers are fundamental in helping to overcome this. Frequency shifters can also help. In Electronics, a circuit arrangement in which a portion of the output of an amplifier is fed back into the input. Negative feedback reduces amplifier gain but also decreases distortion, positive feedback increases the gain and may lead to self-oscillation. Video Feedback is visual distortion of the picture caused when a video signal re-enters the input device, usually a camera and becomes over amplified
Feeder cable: The cable which feeds or supplies power to a dimmer rack, usually heavy gauge cable capable of safely carrying the hundreds of amps necessary to supply as many as 96 individual dimmers in a rack and are usually connected via Camlock connectors.
Fiber optic: A transmission medium designed to transmit digital signals in the form of pulses of light. Fiber optic cable is noted for its properties of isolation from radio frequency and electromagnetic interference, as well as resistance to electrostatic contamination.
Field: A field is one half of a standard television frame, containing every other line of information. Each standard video frame contains two interlaced fields, sometimes referred to as field 1 and field 2. In the NTSC video system, a field contains 262.5 lines and a frame contains 525 lines. In the PAL video system, a field contains 312.5 lines and a frame contains 625 lines.
File: In computers, a record of related information that may be stored in memory, on a disk, or other media. Files can contain text, graphics, data, or programs.
Fill light: Fill lights provide a soft-edged field of light used to provide additional subject illumination to reduce harsh shadows or areas not highlighted by the key light
Film Chain: A device that transfer a film image to a video image. It is also known as a Telecine chain
Filter: In general, a filter accepts the desired and rejects the undesired. Every filter has a specific purpose. In electronics, for example, if you have some high frequency noise mixed with the signal that you want, then a lowpass filter is used to pass the signal and reject the (high frequency) noise. In software, a filter allows the application to open a file of a specific format.
Firewall: A device that isolates and protects a network from outside intrusion.
FireWire: Also known as 1394 or IEEE-1394. A data communication standard used with digital camcorders, the 1394 FireWire manages the digitization, compression and audio synchronization processes while shooting. This puts broadcast quality video footage directly into your computer or DV (digital video) editing system. FireWire supports data transfer rates of 100 to 400 Mbps.
First surface mirror: The front of a mirror. In mirrors intended for A/V applications, the first surface is coated with a reflective material to prevent double images (ghosting).
FL: Focal Length. The distance between the center of a lens and the point where the image comes into focus. In projection, a shorter focal length yields a larger image on the screen for any given projection distance.
Flag: A metal flap used near a lens to keep lights from shining directly into the lens and causing lens flare.
Flagging: Image distortion of a picture during playback that makes the top of the picture looks as if it is bending or waving.
Flare: Dark or coloured flashes caused by signal overload through extreme light reflections of polished objects or very bright lights
Flash memory: A special version of an EEPROM that can be rewritten while in its functioning environment, instead of having to be removed and reprogrammed in a special device. Example: memory for a digital camera.
Flat: Term used to describe an even frequency response, one in which no frequency is accentuated.
Flat panel monitor: Monitors that have a flat display screen utilizing Liquid Crystal Display technology, rather than standard CRT projection. The flat panel is much less susceptible to glare than a standard curved monitor
Flicker: An alternating change of light intensity, typically perceived at a rate of a few Hertz to 60 Hz when viewing static images such as text. Flicker can occur when the electron gun paints the screen too slowly, giving the phosphors on the screen time to fade before being refreshed. This may occur when the refresh rate of the video is too low, or when the persistence of the display device is too short. A fluorescent light fixture may produce the same effect.
Fluid head tripod: A camera tripod that has the pan & tilt motions of its head dampened by a viscous fluid to smooth its movement, the tension of each direction is adjustable
Fly away: A lighting design term referring to a cue in which automated lights move upward away from the stage in a sweeping motion
Flying erase head: In order to facilitate smooth, seamless edits whenever the camcorder recording begins. the erase head is mounted on the spinning (flying) video head drum.
FM: Frequency Modulation. A method of combining an information signal with a carrier signal so that it may be transmitted. FM radio is frequency modulated. Audio is encoded on the carrier by varying the frequency in response to the audio.
Focal Length: The distance between the secondary principal point in the lens and the plane of the imaging device, the longer the focal length, the narrower is the angle of view
Focus: To adjust a lens to make the image appear sharp and well defined. The best possible resolution of an image, showing the image to be sharp and well defined.
Focus coil: Deflection coil. An electromagnetic coil that surrounds a video tube and bends the electron beam onto a screen.
Fog Machine: A device which creates fog by vaporizing a fluid into a fine atmosphere through a heat exchange system and can create effects similar to haze machines, dry-ice or liquid nitrogen foggers, oil crackers, etc, but are best at producing large volumes of dense atmosphere quickly. Use of these machines with video projectors present can produce expensive damage to the video projector optics and internal display panels.
FOH: Front of house; the front of an auditorium, the opposite end to the stage. Typical mixing point for live shows.
Foldback monitors: Wedge-shaped speakers placed on stage so that performers can hear themselves (and the band). Also see "Foldback System."
Foldback System: A cue system that is independent of the main house system. Used both for performers (so they can hear the band and themselves) and for the band (so they can hear the performers and themselves).
Followspot: A narrow-beam focusing instrument that is manually operated, and usually comprises a powerful light source, an iris, shutters, a color changer and perhaps other features
Foot candle: A unit of illumination from one candle at a distance of one foot. Equal to one lumen incident to one square foot.
Foot lambert: The luma (brightness) resulting from a surface emitting a luma flux of one lumen per square foot. The luma of a perfectly reflecting surface receiving an illumination of one foot-candle.
Frame: In interlaced video a frame is one complete picture. A video frame is made up of two fields, or two sets of interlaced lines. In film, a frame is one still picture of a series that makes up a motion picture.
Frame synchronizer: A digital electronic device which synchronizes two or more video signals. by using one of its inputs as a reference and genlocking the other video signals to the reference's sync and color burst signals
Freeze (frame): Special effect in which the picture is held as a still image
Frequency: The number of times a particular event happens per a given time. In A/V, the number of complete cycles per second of a musical tone or electronic signal, expressed in Hertz (Hz).
Frequency range: Refers to the low-to-high limits of a device, such as a computer, projector or monitor. Also see Bandwidth.
Frequency Response: The range between the upper and lower limits that a device or system will adequately transmit (within a range, such as + /; 3dB).
Fresnel lens: A thin, flat lens made by cutting concentric circular grooves into its surface. The grooves act like prisms to bend and focus light. The Fresnel lens is often used for the condenser lens in overhead projectors and in studio spotlights.
Front porch: The black or blanking portion of the composite picture signal lying between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding horizontal sync pulse. See Blanking.
Front projection screen: A light-reflecting screen used when the image is projected from a source in front of the screen. Also see Rear projection screen.
Front screen projection: To project an image from the audience's side of a light-reflecting screen.
FTP: File Transfer Protocol. A protocol used to transfer files over a TCP/IP network (Internet, UNIX, etc.). For example, after developing the HTML pages for a Web site on a local machine, they are typically uploaded to the Web server using FTP.
Full Duplex: The ability of a device or line to transmit data simultaneously in both directions.
Full Duplex Operation: When data is being both sent and received simultaneously. (i.e., sound cards, network interface cards, hubs)
Fully loaded: Refers to the condition when all inputs (in the case of a switcher) or all outputs (in the case of a distribution amplifier) or both (in the case of matrix switchers) are connected to loads/devices, that is, the product has a maximum load connected. This is pertinent because if a product is not properly designed, the voltage and the bandwidth can decrease and the signal can drop out as more and more loads are connected, or crosstalk can be a greater problem as more signals appear on the inputs or outputs.
Function keys: Keys that are programmed to perform specific tasks, such as macro-operations.

G

Gaffers tape: A strong adhesive tape used in film and television production, and in live event staging. As the saying goes, 'If you can't fix it with gaff, it's not worth fixing'
Gain: (1) A general term for an increase in signal power or voltage produced by an amplifier. The amount of gain is usually expressed in decibels above a reference level. Opposite of attenuation. (2) The amplification of a signal, unit, or system. Expressed in the unit of measurement appropriate to the signal or system, or in a mathematical formulation (YxZ) for screens.
Gain, unity: A condition in which the output level is equal to the input level. A gain of 0dB. "Sound nirvana." Op-amps operated at unity gain do the least amount of work and introduce the least amount of noise into the circuit.
Gamma: The light output of a CRT is not linear with respect to the voltage input. The difference between what you should have and what is actually output is known as gamma.
Gamma correction: Before being displayed, the linear RGB data must be processed (gamma corrected) to compensate for the gamma of the display.
Gang: Refers to the number of wiring devices that can be installed in an electrical box, (e.g., "two gang" refers to a box that can accommodate two duplex receptacles, "three gang" refers to a box that can accommodate three duplex receptacles, etc).
Gateway: A device that interconnects networks with different, incompatible communications protocols.
Gel: A term used loosely to describe expendable color filters used in stage lighting, originally made of thin sheets of dyed gelatin, color filters are now made from polymer plastics
Generation: The number of duplication steps between an original recording and a given copy.
Generation Loss: When an analog master videotape is duplicated, the second-generation copy is usually inferior in some way to the master, appearing as loss of detail, improper colors, sync loss, etc
Genlock: A method of synchronizing video equipment by using a common, external signal. This locks the sync generators of multiple devices to a single source.
Geometry: The ability of a projector to accurately reproduce the border around a rectangle image
Ghost: Also called "ghosting," or "reflections." A shadowy or weak duplication of the original image. It can be the result of transmission conditions where secondary signals are created and then displayed earlier or later than the original signal. Ghosts can also be the result of burning an image on a screen or by a mirror.
GHz: Gigahertz. One billion cycles per second.
Giga: The prefix abbreviation for billion. (G) One G-byte = 1 billion bytes.
GLI: Ground Loop Isolator/Inhibitor. Devices that isolate the (video) signals from any system ground problems.
Gobo: A piece of metal or glass, which fits into the gate of a profile spot (qv) and projects a pattern onto the set. Most basic gobos are made of metal but very complex patterns can be created on glass gobos.
Graphic Equalizer: An equalizer that has slider-level controls; once set, the sliders represent the response curve. Changes the relative levels of frequencies.
Grip: The crew member principally responsible for the transportation, maintenance and mounting of the camera
Ground Lift: A process used to eliminate ground loops in systems whereby one or more of the many grounds in the system is disconnected. A switch on a direct box that lifts the ground by disconnecting pin one of the XLR connector. WARNING: NEVER cut or otherwise disable the grounding pin on the AC cord-; if a ground fault should occur in the equipment, the potential for electric shock is enormous.
Ground Loop: audio; A state where too many grounds of equipment are connected at different points. The ground potential starts running around the equipment in loops, causing a mains-frequency (60Hz in the U.S.; don't forget the harmonics) hum in the equipment.
Ground loop: video; A potential system grounding problem that may produce symptoms that appear as sync noise and cause a horizontal bar (hum bar) to roll vertically on the video image. A ground loop occurs when some devices in a system are not connected to the same electrical ground as the other devices. This can create a voltage potential difference between ground on the pieces of equipment. See Ground Lift.
Group Delay: A phenomenon involving timing differences between video signal components.
GUI (Graphic User Interface): A graphical representation of system or device menus and functions that allow the user of a system to control its operation.
GVIF: Gigabit Video Interface. A transmission and connectivity standard developed by Sony that is used for digital video connections on the Sony VAIO desktop computer systems and Sony laptop PCs.

H

H: See Horizontal sync.
H.320 Videoconferencing on ISDN: The H.320 standard has been in place for a decade and videoconferencing today is most commonly implemented on ISDN, providing high quality because its synchronous nature with very low delay and delay variation. ISDN is able to implement videoconferencing at transmission rates from 64Kbps up to 2Mbps. At 128Kbps, videoconferencing on ISDN is only of marginal quality and cannot really be considered suitable for most business uses. ISDN-based videoconferencing at 384Kbps can be considered the baseline of business quality videoconferencing and provides a high quality transmission of videoconferencing. The implementation of ISDN at speeds of 384Kbps and above is costly and a complex undertaking. Three 128Kbps Basic Rate ISDN (BRI) interfaces must be used for every videoconferencing device. Using a device called an IMUX, these three BRI lines must be bonded together to form a single communications channel. This standard is used today by about 90% of all videoconferencing users.
H.323 Videoconferencing on Frame Based Networks: The standard H.323 was designed for videoconferencing on frame based networks (Ethernet, Token Ring, FDDI, ATM) using TCP/IP protocol. Today H.323 normally does not provide as high quality videoconferencing as H.320.
H.310 Videoconferencing: H.310 is a MPEG-based videoconferencing and is different from H.320 and H.323. A two-way MPEG2 videoconferencing at up to 15Mbps (with a latency of about 150ms) is like watching TV! It requires up to 15Mbps of bandwidth and the hardware costs signficantly more.
Half duplex: Data transmission that can occur in two directions over a single line, but only one direction at a time.
Handshake: A term used in communications that refers to the activity that takes place when the transmitting and receiving devices identify themselves to each other.
Hardware: Physical equipment.
Harmonics (in music: overtones): Multiples of an original frequency that add to and modify the original frequency. A pure sine wave is free of harmonics. When harmonics occur in electronic signals, it adds distortion to the original signal, causing undesirable results.
Haze machine: A device, similar to a fog machine, which produces a light, fine atmosphere by atomizing a special haze fluid. The atmosphere produced by a haze machine is dense enough to reveal beams of light in the air, but not so dense as to become opaque. The use of this type of machine can cause expensive damage to the optics and internal display panels on video projectors.
HD connector: A high-density D connector having its pins arranged close together, sometimes in three rows instead of two rows. Example: a 15-pin VGA connector (HD) vs. a Mac connector (D).
HDTV: High Definition Television. HDTV refers to a complete product/system with the following minimum performance attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reproduces, and/or outputs Dolby Digital audio.
HDTV Monitor: High Definition Television Monitor. HDTV minus ATSC tuner and Dolby Digital audio.
Helical scan: A method of recording video information diagonally on a tape where the high speed rotating video heads scan these diagonal video tracks, giving an effective tape speed much higher than the actual tape speed allowing more information to be recorded on a given length of magnetic tape
Hertz (Hz): The international term for cycles per second.
Hi-8: A Sony videotape format using 8 mm tape. High quality and compact, Hi-8 is marketed for ENG (Electronic News Gathering).
High fidelity: Hi fi, accurate, and faithful reproduction of the original. Absence of distortion or enhancements.
High impedance: Hi Z or high Z. A relative term that is different for each application. In video, when the signal is not terminated it is said to have a Hi Z load. Hi Z is typically 800 to 10k ohms or greater.
Hiss: The most common audible noise component in audio recording, stemming from a combination of circuit and tape noise, can be mitigated to some extent by noise reduction systems such as Dolby.
Hooking: See Bending.
Horizontal blanking: After making a scan line (left-to-right), the electron beam in a CRT retraces (returns) to the left side of the screen to begin the next line. During retrace time, it is not putting picture information on the screen, so the beam is turned off, or blanked. About 83% of each horizontal cycle is spent writing the line, while 17% is spent retracing the beam to the left before starting the next line. See Blanking.
Horizontal centering control: Adjusting the horizontal centering control shifts the displayed image left or right on the display screen. Also called "horizontal shift."
Horizontal double images: A video problem when the display is split down the middle with two identical, but squeezed images displayed on each side of the screen.
Horizontal filtering: In some scan converters and other products, this is a feature that controls the sampling of the horizontal plane, thereby affecting the sharpness or smoothness of the scan-converted picture.
Horizontal rate: Horizontal scanning frequency. The number of complete horizontal lines (trace and retrace) scanned per second. Measured in kHz, the NTSC standard is 15.75 kHz.
Horizontal resolution: The number of vertical lines that can be perceived in a video device.
Horizontal sync (H or HV): The pulses that control the horizontal scanning of the electron beam in a video device. Horizontal (H) sync, or horizontal and vertical sync combined (HV). On connector panels, "H" identifies the connector for horizontal sync, and "H/HV" means it is also used for combined or "composite" horizontal and vertical sync (RGBS).
Hot spot: Commonly seen on high-gain screens and screens designed for slide or movie projection, a hot spot is a circular area where the image is brighter than the rest of the screen. The hot spot is always located along the line of sight, and "moves" with the line of sight.
Hot-swap: The ability to change electronic components, such as circuit boards or peripheral devices, without removing power from the device.
House sync: See Black burst.
HSB: Hue-Saturation-Brightness. In color graphics, Hue = the color; saturation = the amount of color; and brightness = the amount of white.
HTML: Hypertext Markup Language. A formatting computer language used to create web pages.
HTTP: Hypertext Transfer Protocol. Protocol used for web page retrieval from a web server.
Hue: (1) Color value or saturation, as opposed to brightness or intensity (2) Tint control; Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control adjusts the amount of color displayed. See HSB.
Hum: The coupling of an unwanted frequency into other electrical signals. In audio, hum can be heard; in video, it can appear as waves or bars in the picture. Often it is an audible disturbance caused by the power supply, or an improper ground.
Hum bar(s): Interference in the form of a horizontal bar moving vertically on the display screen. Hum bars can be caused by ground loops.
Humbucker: A transformer used to isolate video signals caused by interference from hum bars or moir�.
HV: See Horizontal sync.
Hypercardioid microphone: A directional microphone with greater attenuation at the sides than a pure cardioid pattern, but with less attenuation at the rear.

I

IATSE: The International Alliance of Theatrical Stage Employees. The international bargaining unit for stagehands such as property masters, audio techs, carpenters, riggers, electricians, wardrobe mistresses, etc., etc.
ICIA: International Communications Industries Association. A professional A/V, video and multimedia industry association. Formerly National Audio Visual Association (NAVA). www.infocomm.org
Icon: An on-screen symbol that visually represents a program file, data file, or some other computer entity or function in a graphical user interface.
ICWK: Internal Computer Wiring Kit. Custom ICWK kits provide interfacing signals for computers and terminals that have no video display output connector.
ID bit termination: ID bit termination is used to indicate (identify) what type of device (what type of monitor) is attached to a computer-video output port or at the end of a daisy chain. ID bit termination involves connecting specific data lines/pins to the electrical ground. For example, VGA-type displays use pins 4, 11, and 12 for ID bits; but pins 4, 7, and 10 are used for Macintosh ID bits; and pins 3, 4, 8, and 9 are used for many Sun display devices. ID bit termination assures that the correct video signals will be sent to the display device. A computer checks for ID bits during the power-up self diagnosis, and sets the video output frequency and resolution based on how the ID bits are set. Some computers will not send any video signal if they do not sense any ID bits on boot-up, so no picture will be displayed. ID bits are also called "sense lines."
IDTV: Increased Definition Television. Example: scan doubling or scan quadrupling.
IEC: International Electro-technical Commission. The body that has responsibility for developing international A/V standards. ICIA cooperates with IEC sub-committee SC-60.
IEC connector: The standard AC power connector used on power supplies in computers and other electronic equipment. It accommodates a power cord with a connector on both ends.
IEEE: The Institute of Electrical & Electronics Engineers promote the engineering process creating, developing, integrating, sharing, and applying knowledge about electrical and information technologies and sciences for the benefit of humanity and the profession.
IEEE 802.3: The Institute for Electrical and Electronics Engineers standard for Ethernet networks.
IEEE 1394: Institute of Electrical and Electronics Engineers 1394. Also known as FireWire, a serial digital format that handles a wide range of data. IEEE 1394 offers peer-to-peer interface capability, so it does not require computer support.
ILA�: Image Light Amplifier. Used in their large screen projectors, a Hughes/JVC device that uses low-intensity images to modulate high-intensity light through a liquid crystal layer.
Image: A reproduction or imitation of a person or thing displayed by any type of visual media.
Image stabilization: A camcorder feature which takes out minor picture shakiness, either optically or electronically.
Impedance: The opposition or load to a signal, measured in ohms and abbreviated W or Z. In video, typical low impedance circuits (low Z) are 600 ohms or less and high impedance circuits (high Z) may be 10k ohms or greater. Video termination impedance is 75 ohms. See High impedance and Low impedance.
Impedance-matching: Circuits that generate audio or video signals are designed to work with a certain load (impedance). When connecting devices in a system, it is important that the impedance specifications are adhered to. If the impedance of the load is not matched to that of the source, there could be undesirable results, such as loss or distortion of the original signal, reflections, etc.
IMUX: Inverse multiplexer. A unit that combines multiple low bandwidth digital phone lines into a single high bandwidth call.
Inductor: An electrical component that opposes changes in current flow and stores electrical energy as a magnetic field. Although all wires have inductive properties, an inductor component is usually a coil of wire. Transformers use this same principle.
Infrared (IR): Light waves just outside the visible spectrum, slightly longer than those visible to the human eye. Infrared light is sometimes filtered out to reduce heat on film or slides. See Infrared control.
Infrared control: A wireless medium of remote control, which sends signals to a device via pulses, transmitted in the infrared light spectrum. Its use is restricted to equipment within line-of-sight or reflections off a wall or ceiling. This is sometimes called "IR remote."
Input: A source for data or a signal to be used by another device. The physical connector or port for entering such a signal or data is called the input.
Input Channel: The section of a mixer which receives the signal from microphone, tape deck, etc.
Input sensitivity: The minimum input level signal required to output a specified output level.
Insert editing: Camcorder/VCR feature which allows a user to insert new audio/video segments into the middle of a previously recorded tap.
Insertion loss: The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Insertion loss is usually expressed in dB. In an optical fiber system, insertion loss is the total optical power loss caused by insertion of an optical component, such as a connector, splice, or coupler.
Interface: (noun) A device or module that operates as a link between dissimilar modules, usually because those modules cannot communicate directly with each other. An interface may act as a translator or interpreter and could be in the form of hardware and/or software. A computer video interface allows computer-video signals to be used by large screen video displays.
Interlacing: A video frame is made up of two fields. Interlacing is the process of scanning the picture onto a video screen whereby the lines of one scanned field fall evenly between the lines of the preceding field.
Interleaving: The process of assigning consecutive physical memory addresses alternately between two memory controllers in order to increase the effective transfer rate.
Inverse-Square Law: Pertaining to any condition in which the magnitude of a physical quantity follows an inverse relationship to the square of the distance. For point sources of sound, the SPL drops 6dB for every doubling of the distance.
I/O: Input/Output. Refers to the flow of information or signals (in or out) with respect to a particular device.
IP address: In the most widely installed level of the Internet Protocol today, an IP address is a 32-binary digit number that identifies each sender or receiver of information that is sent in packets across the Internet. When you request an HTML page or send e-mail, the Internet Protocol part of TCP/IP includes your IP address in the message (actually, in each of the packets if more than one is required) and sends it to the IP address that is obtained by looking up the domain name in the Uniform Resource Locator you have requested or in the e-mail address you're sending a note to. At the other end, the recipient can see the IP address of the Web page requestor or the e-mail sender, and can respond by sending another message using the IP address it received.
IP NUMBER/ADDRESS (Internet Protocol Number/Address): Sometimes called a dotted quad. A unique number consisting of 4 parts separated by dots, e.g. 165.113.245.2 Every machine that is on the Internet has a unique IP number; if a machine does not have an IP number, it is not really on the internet. Most machines also have one or more Domain names that are easier for people to remember
IPX: Internetwork Packet Exchange Protocol. Commonly used over Novell Netware and Microsoft Windows networks.
IR learning: The ability of a device to receive and store infrared commands for other devices, such as the projector.
IR library: Sets of infrared commands for remote controlled devices.
IRE: Institute of Radio Engineers, formerly called IEEE.
IRE scale: An oscilloscope scale that applies to composite video levels. Typically, there are 140 IRE units in one volt (1 IRE = 7.14 mV). This makes luma level values easier to communicate. The amplitude of the video signal from blanking (zero volts) to peak white is 0.714286 volts or 100 IRE units. Sync signals extend from blanking to 1.285714 volts/40 IRE units.
ISDN: Integrated Services Digital Network. An international communications standard for sending voice, video, and data digitally over telephone lines. ISDN uses special wires and can transfer at rates of 64,000 bits per second. Another version called B-ISDN uses fiber optics and can transfer at 1.5 megabits per second.
Isolation: In electronic specifications, a measure of how well a signal is protected from interference from other signals. See Crosstalk.
ITU: International Radio Consultative Committee. Formerly known as the CCIR (Comit� Consultatif International des Radiocommunications) or International Radio Consultative Committee. A global organization responsible for establishing television standards.
ITU-R BT.601: Formerly known as CCIR 601. This is a recommendation developed by the International Radio Consultative Committee for the digitization of color video signals. ITU-R BT.601 deals with color space conversion from RGB to YCbCr, the digital filters used for limiting the bandwidth, the sample rate (defined as 13.5 MHz), and the horizontal resolution (720 active samples). CCIR 601 is a serial digital form of component video. It is roughly equivalent to Y, R-Y, B-Y, but it is digital instead of analog and is transmitted on one coax cable, instead of three. It is also called 4:2:2, which refers to the number of samples taken from the video channels respectively, in order to digitize and encode it. They sample the Y at four times the speed of the video (which is roughly 6 MHz) and the R-Y and B-Y are sampled at 2 times the speed of the video. The sample values are encoded into 10 bit words and then transmitted serially, over one line, hence serial digital.

J

Jack: Term for terminating point of a circuit. A common term for a female phone plug connector.
Jaggies: A video problem in which stairstep-like lines appear where there should be straight-angled lines or smooth curves. See Aliasing.
Jitter: A video problem in which the displayed image is unstable or appears to shake.
JPEG: Joint Photographic Experts Group. A committee formed as a joint effort between the International Standards Organization (ISO) and CCITT that developed a standard for the still digital image compression/decompression for use in computer systems.
JPEG: File compression standard. The JPEG image size may be reduced by as much as 30:1 with some loss of data. It does not work well with line art, text, or vector graphics. The file extension is ".jpg."
Judder: A distracting side effect of 3:2 Pulldown Detection or "Inverse 3:2 Pulldown" that occurs as a result of every other film frame lasting 1/60 of a second longer than the previous one.

K

K: kilo. An abbreviation for 1,000. A kilobyte is 1,000 bytes. Because numbers used in computer RAM sizes are in binary, the closest number is used. When talking about memory size, the numbers are rounded off (e.g. 1 kbyte is really 1,024 bytes).
Kelvin: This is a system or scale used for measuring temperature. Absolute zero is 0 degrees Kelvin or -273 degrees Celsius. The color of white light is expressed in terms of degrees Kelvin, the color of light emitted when an ideal object is heated to a particular temperature.
Key: (1) Also called key source or key cut. A signal that can be used to electronically cut a hole in a video picture to allow for insertion of other elements such as text or another video image. The key signal is a switching or gating signal for controlling a video mixer that switches or mixes between the background video and the inserted element. (2) The composite effect created by cutting a hole in one image and inserting another image into the hole.
Key light: The term used to describe a subject's main source of illumination
Key fill: In key effects, the video signal that is said to fill the hole cut in the background video by the key source.
Keyer: An electronic circuit that creates a control signal to control a video multiplier based on selective information contained in a video signal.
Keystone effect: A distorted picture where one edge is not the same dimension as the opposite edge, producing a tapered, or wedge shape. Typically, this results when the image is projected to the screen at an angle. In stone buildings, the tapered stone at the top of an arch is the key that prevents the arch from falling.
kHz: Kilohertz. One thousand cycles per second (hertz).

L

Lambert: A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 foot-candles per square centimeter
Lag: Some camera pickup tubes may retain an image after it is no longer present, this effect is most evident when a relatively bright image is replaced by a darker field of view and is aggravated when a bright image is stationary in the field of view for an extended period of time before it is replaced
LAN: Local Area Network. A local area network is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).
Laser: A device which produces pencil thin beams of coherent monochromatic light, primarily used for special effects, lasers combined with beam splitters, scanners, and mirrors can be used to create a variety of three-dimensional images in fog or similar atmosphere.
Latent image: The image retained by a pickup tube after the source of that image is removed. If a latent image is present on a pickup tube when a camera is turned off, the image may be permanently fixed on the tube.
Lavalier Microphone: A miniature microphone that is designed to be attached to the user's clothing via a clip. Often used in newscasts or productions requiring unobtrusive amplification. Can also be hidden in clothing, hair, over the ear, in plants or pocketbooks, etc.
LBC: Laptop Breakout Cable. The cable that connects a computer laptop to a computer-video interface.
LCD: Liquid Crystal Display. A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between them. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing.
LCD projector: Utilizing the LCD technique, these projectors separate the red, green, and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.
LCoS: Liquid Crystal on Silicon. This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry.
LD: Line Doubler. An Increased Definition Television (IDTV) feature that doubles the number of scan lines in a video picture. This fills the space between the original lines, making them less noticeable, and increases the brightness of the picture. For example, the NTSC video field of 262.5 lines is doubled to 525 non-interlaced lines and the PAL field of 312.5 lines becomes 625.
Leko: A commonly used term for an ellipsoidal spotlight. Named after its inventors Levy and Kook.
Lens hood: A cone fastened to the front end of a lens to keep incident light from striking the lens elements and causing lens flare.
Lenticular screen: A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.
Lenticulation: A cylindrical lens which causes light passing through it to be dispersed perpendicular to its axis.
Level: The relative intensity of an audio or video source.
Level control: The level control on some interface products is similar to the contrast control on a data monitor. It can either increase or decrease the output signal level from the interface to a data monitor or projector. This results in greater or less contrast in the picture.
LED: Light Emitting Diode. A low-power, long life, light source, usually red, green, or yellow in color. Some LEDs can produce two different colors.
Light level: The intensity of a given lighting situation as measured in foot-candles (Ft-c).
Limiter: An amplifier designed to limit or compress signals over a desired level, thus reducing the chances of distortion and keeping the range of signal levels within the range that can be recorded.
Line input: Any input designed to accept a line-level input signal.
Line level: Preamplified signal, in contrast to microphone level. The actual signal levels vary, with nominal microphone level being -50dBM and nominal line level being +4dBM.
Line out: Audio output. In consumer systems, this may be 10,000 -50,000 ohms, at -10dB or -20dB.
Line voltage: Alternating current (AC) at the level typically found in the home.
Linear editing: Editing using a media like tape, in which material must be accessed in the order that it was created.
line compensation: Use of a video line amplifier to pre-compensate for high frequency video signal transmission losses resulting from long distance cable runs by boosting those signal frequencies most affected.
Linearity: The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen but a different size when it is at the bottom of the screen.
Load in: The process by which all of the physical elements of a show are unloaded from a truck and installed at a venue for a performance.
Load out: The process by which all of the elements of a production are struck from the venue and loaded onto a truck
Load resistance: The impedance or resistance (load) that a cable places on a signal being transmitted through it.
Login: The authentication information required to gain access to a network resource.
Longitudinal Wave: A wave in which the vibrations are in the direction of propagation of the wave; i.e. sound waves in air.
Looping: A term used to describe the chaining of a video signal through several video devices.
Loop-through: A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording device(s). Loop-through connections are found on some scan converters and scalers.
Lossless: When using compression to reduce text and/or graphic files, some techniques discard data in the process. Methods that compress files without losing data are called lossless. Examples include LZW (Lempel-Ziv Welch), PKZIP, or Zip 8-bit.
Lossy: A term to describe compression techniques that throw away data as part of the process. The more data loss, the smaller the file, and the lower the quality (grainy or jagged edged) the image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, high means high compression (greater loss) and low means low compression (less loss).
Low impedance: The condition where the source or load is at a lower impedance than the characteristic impedance of the cable. Low source impedance is common; low load impedance is usually a fault condition. Example: 30; 600 ohms.
Low-pass filter: A filter designed to pass low frequencies with little or no attenuation.
LSTA: Laptop Sync Termination Adapter. A pass-through VGA-style (15; pin HD connectors) adapter that provides 510 ohm termination for horizontal and vertical sync signals. Most small digital projectors are designed to be near the video source (short cables). This adapter is used to eliminate jitter and/or intermittent tearing in the displayed image by providing sync termination for long cable runs.
LTC (Longitudinal Time Code): SMPTE (Society of Motion Picture and Television Engineers) time code standard usually recorded onto the linear audio track of a VCR or audio tape machine
Luma: Also called Luminance. The photometric radiance of a light source. The luma signal represents brightness in a video picture. Luma is any value between black and white and is abbreviated as "Y." See Chroma.
Luma delay: A video problem in which the intensity of an object or area is shifted slightly to the right of the color. The color occurs in the correct area of the displayed image, but the luma (intensity) starts later.
Lumen: (LM) A unit of measure for the amount of light emitted by a source. 0.98 Ft-c (foot-candles) of light covering a surface of 1 square foot.
Lux: The amount of light per square meter, incident on a surface. The term applied to metric measurement of light intensity taken at the illuminated surface. One foot-candle (Ft-c) = 10.76 lux, or 1 lux = 1 lumen/square meter = 0.093 foot-candles.
LVDS: Low Voltage Differential Signal. A signal transmission standard developed for the connection of laptop computers to their local LCD displays. National Semiconductor is the manufacturer that is promoting this standard. SGI used LVDS on the 320 and 540 NT Visual Workstations for connection to their 1600SW series, 6x9 aspect ratio, LCD monitor.
LZW: Lempel-Ziv Welch. A lossless method of file compression.

M

M or MB: Mega. An abbreviation for one million.
MAC address: Media Access Control address. The MAC address is a computer's unique hardware number.
Macro focus: Zoom lenses which allow you to get as close as one or two inches to your subject.
Magnetic deflection: A method of altering the path of an object (such as an electronic beam) with a magnetic field. CRTs have magnetic coils that carry currents that create magnetic fields that control the path of the electron beam. Also called "magnetic focus."
Magnetic focus: See Magnetic deflection.
Magnetic Induction: The generation of an electrical signal in a conductor caused by relative motion between the conductor and external magnetic lines of force. When a conductor (wire) moves within a magnetic field and cuts across the magnetic lines of force, a voltage will be set up or "induced" across this conductor. Also, when a stationary conductor is placed in an oscillating magnetic field, a voltage is induced across the conductor.
Masking: The obscuring of one sound by another or the obscuring of an image by a flag or other opaque device.
Matrix: An electronic device that accepts and distributes video and/or audio signals selected from multiple inputs and multiple outputs. See Matrix switcher.
Matrix switcher: A means of selecting an input source and connecting it to one or more outputs. Like a regular switcher, but with multiple inputs and multiple outputs.
Matte white: A screen with a flat, dull surface for even reflection over wide viewing angles.
MB: Megabyte. A megabyte is actually 1,048,576 bytes, or roughly a million bytes.
MBC: Monitor Break-out Cable. A cable used to view a computer signal on a local monitor or terminal while routing the same signal to a new source, such as a data projector or monitor. An MBC provides three connections in the form of a "Y" cable, a "T" cable, or through a buffer in an enclosure box.
Mbps: Megabits per second. One million bits per second; a unit of measurement for data transmission.
MDA: Monochrome Display Adapter. Resolution 720 x 350. A graphics card found in the IBM PC and PC XT; AT series.
Megapixel: In digital imaging devices, megapixels define the resolution range when the number of pixels is equal to or greater than 1,000,000 pixels. For example, SXGA is 1280 x 1024, or 1,310,720 pixels. This could be called a 1.3-megapixel device.
MFTA: Multi-Frequency Termination Adapter. A single termination device with selectable frequencies for different applications.
MHz: Megahertz. One million hertz (cycles per second). Video bandwidth is measured in megahertz.
Microphone: A transducer for converting acoustic energy to electrical energy.
Microphone Level: A signal coming out of the microphone's diaphragm. It has not been preamplified yet, in contrast to line level. Actual level can be anywhere from -60dBM to -20dBM.
MIDI: Acronym for "Musical Instrument Digital Interface." A digital communications standard established in 1984 by musical instrument manufacturers Yamaha, Roland, and a few others. Enables communication (i.e. note on, note off, velocity, etc.) between musical instruments. MIDI has expanded to include communication with lighting boards, computers, sequencers, consoles, effects processors, and the like.
Milli: m. Abbreviation for one one-thousandth. Example: 1 ms = 1 millisecond or 1/1000 second.
MIPS: Million instructions per second. The rate at which a computer executes instructions.
MMI: Motion Mode Interpolation. Eliminates scan lines and jaggies in line doublers.
(M)NTSC: This is the color video standard used in North America and some other parts of the world created by the National Television Standards Committee in the 1950s. A color signal must be compatible with black-and-white TV sets.
Modem: Modulator/demodulator. A device that puts information on a carrier signal and transmits it over a (phone) network. The same device receives such signals and demodulates, or separates the information from the carrier. A modem connects computers with other communication devices through ordinary phone lines.
Modulation: The process of adding an information signal to a carrier frequency to allow it to be transmitted. Thus, the carrier is modulated by the information signal, as in a modem.
Moir�: A pattern resulting from a combination of other patterns. In video, this is usually an undesirable pattern caused by an unwanted signal interfering with the desired signal. This may appear as a wavy motion.
Momentary contact: A non-latching contact closure that lasts as long as it is held in place.
Momentary switch: A switch that returns to its normal circuit condition when the actuating force is removed.
Monitor: (1) A TV that receives a video signal directly from an external source, such as a VCR, camera, or separate TV tuner to produce a high-quality picture. (2) A video display used with closed circuit TV equipment. (3) A device used to display computer text and graphics.
Monitor/receiver: A TV having RF tuning circuits to receive broadcast signals for viewing.
Monochrome: One color, usually interpreted as black and white. In computer CRTs, it is any single color with black.
Monochrome composite output: Provides a monochrome video output with combined horizontal and vertical sync for composite video with all the shades of the computer's monochrome, 8-, 16-, or 64-color display adapter card output signal.
Monochrome signal: A video signal having one color, usually a black and white signal or sometimes the luma portion of a composite or component color signal.
Mosaic: Special effect in which the picture is divided up into tiles.
MP3 (MPEG-1, Layer 3): Using MPEG audio, one may achieve a typical data reduction of 1:4 by Layer 1, 1:8 by Layer 2 & 1:12 by Layer 3, MPEG Layer-3 is the most powerful member of the MPEG audio codec achieving the highest sound quality.
MPCD (Minimum Perceptible Color Difference): This is a unit of measure, developed by the CIE, to define the change in light and color required to be just noticeable to the human eye, the human being is defined as "a trained observer" because there are differences in the way each of us perceives light.
MPEG: Motion Picture Experts Group. A standards committee under the auspices of the International Standards Organization working on algorithm standards that allow digital compression, storage and transmission of moving image information such as motion video, CD-quality audio, and control data at CD-ROM bandwidth. The MPEG algorithm provides inter-frame compression of video images and can have an effective compression rate of 100:1 to 200:1. It is also the acronym given to a family of International Standards used for coding audio-visual information in a digital compressed format; standards include MPEG-1, MPEG-2 and MPEG-4.
MTBF: Mean Time Between Failures. A basic measure of reliability for repairable items. It can be described as the number of hours that pass before a component, assembly, or system fails. Also (MTBR) Mean Time Between Repairs
Multipoint: When more than two locations are connected for a videoconference using a bridge. Usually multipoint switching is done by video-follow-audio, such that the person speaking is automatically seen by the other conference site(s).
Multiplexor: An electronic system that can accept a number of camera inputs and record them virtually simultaneously, and can also provide multi screen displays with four, nine, sixteen etc. cameras on the screen at once
Multi-scan monitor: A monitor (also referred to as multi-sync) which synchronizes to different video signal sync frequencies, allowing its use with various computer video outputs.
Multi-standard monitor: A monitor which synchronizes to different video signal standards such as NTSC and PAL.
Mute: Usually, a switch on a device that silences the input/output in question. Some consoles with varying degrees of automation can mute many channels / outputs at once, with one single touch of a button.

N

NAB: National Association of Broadcasters. The body that sets standards for US broadcast stations. www.nab.org
Native resolution: The resolution at which the video or data file was created, and the specific normal output of a projection device without artificially expanding or compressing the image.
Near end: In videoconferencing, the party or group at the local end of the connection.
Networking: Two or more devices (or people) communicating with each other and sharing resources.
NEXT: Near-End Crosstalk. A measure of interference between the conductors of a cable. A measure of the unwanted signal coupling from a transmitter at the near-end (source end) into neighboring pairs measured at the near end. NEXT loss is expressed in decibels relative to the received signal level.
NIC: Network Interface Card. Piece of hardware, usually in peripheral card form that interfaces a computer to a network.
Ni-cad: Nickel cadmium battery. The oldest rechargeable battery technology currently in use. It provides more charge per pound than lead-acid batteries, but less than nickel metal hydride. It uses a nickel and cadmium plate and potassium hydroxide as the electrolyte.
Node: One specific point or connected location on a network (i.e., a client or print server). A point or line where minimal motion takes place.
Noise: Any unwanted signal that adversely affects the quality of the picture or sound.
Noise bars: White streaks in a picture, usually caused when video heads trace parts of the tape that have no recorded signal, also known as guard bands.
Noise-cancelling: A microphone designed to cancel ambient noise so that it will not be broadcast or recorded. The housing of the microphone allows noise to reach both sides of the diaphragm simultaneously, one side canceling the other out. A close speaking voice strikes the diaphragm on only one side, generating a stronger signal with less background noise.
Noise gate: An amplifier that has a zero output until the input level exceeds a chosen threshold level. Translation: it takes a signal, and if the signal isn't loud enough, it won't let it out. If the signal is loud enough (over the threshold value), the noise gate will let the signal through.
Non-blocking matrix switchers: These are true matrix switchers allowing any input to switch to any or all outputs. They have no switching limitations contingent on hardware or software.
Non-composite video signal: A video signal that contains picture and blanking information only with no sync information.
Non-interlaced: Also called progressive scan. A method by which all the video scan lines are presented on the screen in one pass instead of two. Also see Interlacing.
Non-linearity: The amount by which a measured video signal output differs from a standard video signal output.
Non-linear editing: The process of editing using rapid retrieval (random access) computer controlled media such as hard disks, CD-ROMs and laser discs that allow you to compile the segments out of the order they were created.
Non-segmented: A system of video recording that uses one head to scan one field of video onto the tape.
Normally closed contact: Relay or switch contacts that are closed when the relay is not activated.
Normally open contact: Relay or switch contacts that are open when the relay is not activated.
Notch Filter: audio; A filter that operates a correction at a very specific frequency leaving those around it largely unaffected.
Notch filter: video; A circuit which effectively separates the NTSC black and white information from the color 3.58 MHz carrier signal. The name is based on the fact that the circuit takes a notch out of the frequency band.
NSCA: National Systems Contractors Association. The NSCA is an international trade association of companies specializing in audio, video, security/life safety, presentation, lighting, or other low-voltage systems. This association offers an annual expo. www.nsca.org
NTSC: National Television Standards Committee. The television standard for North America and parts of South America having 525 lines/60 Hz (60 Hz refresh), two fields per frame and 30 frames per second. Technically, NTSC is a color modulation scheme. To fully specify the color video signal it should be referred to as (M) NTSC. NTSC is also commonly (though incorrectly) used to refer to any 525/59.94 video system. See (M) NTSC.

O

OCR: Optical Character Reader or Optical Character Recognition. Hardware and software that reads characters as images and converts them into text to be used in a computer.
Octave: The interval between any two frequencies f 1 and f 2, when f 2 = 2f 1.
Ohm: The unit of electrical resistance, transmitting a current of 1 amp when subjected to a potential difference of 1 volt. Represented by W or Z.
Omnidirectional Microphone: A microphone that is equally sensitive in all directions.
Opaque projector: Uses the principal of light reflection to create an image of any nontransparent object, such as printed pages, coins, photographs single sheets or in book form.
Oscilloscope: A test device that allows measurement of electronic signals by displaying the waveform on a CRT screen.
Output: A product or operation that goes to some external destination, such as another device, a video screen, image, or hard copy. The signal derived from any audio or video device. The physical connection that delivers the result ofwhat the device does, such as an output connector that carries the output signal.
Overhead projector: A device that produces an image on a screen by transmitting light through a transparent material placed on the stage of the projector.
Overload: A state of being in sound land where input levels are too large for whatever they are being sent to, which results in amplifier clipping and distortion, preamp distortion, and generally dirty sound. On a mixer, this state is generally marked by a small red LED located on each channel (the "peak" LED).
Overlay: Keyed insertion of one image into another, such as superimposing computer generated text on a video image, for titling purposes.
Overscan: The result of the TV scan lines exceeding the boundaries of the display screen.
Overtone: A mode of vibration (or, a component of a sound) with a frequency greater than the fundamental frequency.

P

Packet: A collection of network data sent at once from one network node to another.
Pad: see "Attenuator."
PAL: Phase Alternate Line. A television standard in which the phase of the color carrier is alternated from line to line. It takes four full pictures for the color-to-horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors. For this reason, the hue control is not needed on a PAL TV set. PAL, in many forms, is used in Australia, England, Scandinavia, South Africa, and Western Europe. PAL uses 625-line, 50-field composite color transmission system.
PAL-M: Brazilian version of PAL. This is a broadcast standard with 525 lines and 60 fields per second.
Pan-pot: A potentiometer used to vary the balance of a sound source routed to two tracks, either to create the illusion that the source is actually moving between two locations, or to place the source at some fixed location between the two sound sources. On a mixer, the knob that places the sound location between left / right; or group 1 / 2; etc.
PanelLink�-Silicon Image's TMDS: (Transition Minimized Differential Signaling) all-digital video transmission standard. PanelLink technology was designed to provide the bandwidth necessary to support digital displays.
Par lamp: A designation of a type of lamp, one with a parabolic aluminized reflector.
Paragraphic Equalizer: An parametric equalizer with slide-fader control of boost/cut at each frequency. A mix of a graphic and parametric equalizer.
Parametric Equalizer: An equalizer with separate controls for center frequency, bandwidth ("Q"), and boost/cut. Offers greater control of frequency boost / cut than a graphic equalizer. Compare with "Graphic Equalizer."
Passive graphics: A computer graphics operation that takes place automatically and without operator intervention.
Patch: To interconnect (i.e. "I'm going to patch the system now"); a set of interconnections that programs a synthesizer to produce a certain sound; originally meant for use with analog synthesizers, but the name has stuck, and "patch" is used to denote the voices in a digital synthesizer. Can also be used to identify programs within an effects processor.
Patch bay: A control panel where all the video and audio lines are brought together and terminated in connectors allowing any combination of lines to be wired together as desired by patching in short lengths of cable
PC: Personal Computer or Projector Control.
PCC: See "Phase Coherent Cardioid."
PCB: Printed Circuit Board.
PDF: Portable Document Format. A type of format developed by Adobe Systems with which the same file can be opened and viewed on most any computer platform (PC, Mac, Unix). It can also be printed on most any printer (dot matrix, laser, inkjet, PostScript, or non-PostScript). A PDF is a document file in that it includes text and graphics in one file that maintains the appearance of the original.
Peak: The highest or lowest level of signal strength, as determined by the height of the signal's waveform.
Peak white: The whitest portion of a picture signal.
Peaking: A means of compensating for mid; and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. The higher the frequency and longer the cable length, the more peaking may be required.
Peaking control: Peaking control compensates for mid; and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. When using the peaking control a noticeably sharper picture will be seen on all displays regardless of cable lengths. However, 100% peaking may provide over enhancement on short cable runs. Use the position that produces the sharpest image on the display screen. Also called "sharpness" control.
Peak-to-peak: Abbreviated "p-p." The difference in amplitude (voltage, for example) between the most positive and the most negative excursions (peaks) of a signal.
Pedestal: The pedestal is a small DC voltage step within the video signal indicating a picture's black-level and is used as the reference in a standard video signal for white level and all gray levels, normally 0%; 5% of video amplitude above the blanking level.
Peripheral device: Normally an external device that a CPU communicates with, such as a printer, mouse, disk drive, or interface.
Persistence: In video, persistence is the staying power of a lighted phosphor, since a phosphor begins to dim after being excited by the electron beam. A long-persistence screen allows the phosphor to dim more slowly.
PFL (Pre-Fader Listen): Facility to listen to the channel without the audience doing so, useful to check mics and cue tapes. A cue-ing mechanism on a console. See Sound Processing, with the section on consoles.
PGA: Professional Graphics Adapter. Early IBM analog graphics adapter found in the PC AT series. The PGA was capable of producing 256 colors with a resolution of 640 x 400.
Phantom power: Power supplied to a microphone using the shield of a balanced audio connection. Microphones using phantom power must be condenser-style, designed for use with phantom power systems. Damage can result to other types of audio components from the improper use of phantom power.
Phase: The relative timing of one signal to another, usually expressed in degrees of shift.
Phasing adjustment: To properly synchronize an NTSC/PAL video output signal to a genlock signal, a phasing adjustment to the horizontal phase and the subcarrier phase may be required. The horizontal phase difference between these two signals must be set to zero. Likewise, the subcarrier phase difference between these two signals must also be set to zero.
Phase Coherent Cardioid: A type of Pressure Zone Microphone, that, instead of being omnidirectional, is cardioid or even hypercardioid. Great for theatre. The term "Phase Coherent Cardioid" is a registered trademark of Crown, Inc., Elkhart, IN.
Phase error: A change in the color subcarrier signal which moves its timing out of phase, i.e., it occurs at a different instant from the original signal, and will result in a change in the image's hue.
Phase Shift: In the phase relation between one wave and another, phase shift occurs when one wave has been advanced or retarded through its cycle relative to a similar waveform.
Phone Plug: 1/4" diameter connector commonly found as headphone jacks on consumer stereo equipment; used for line inputs and outputs. Occasionally used for speaker connections due to inexpensive cost. Also T/S plug or T/R/S.
Phono Plug: "Pin Plug" developed by RCA (also called "RCA Plug") commonly found as line outputs on consumer stereo equipment. Not used much in pro audio except for tape outputs or inputs.
Phosphor: The chemical coating on the inside of the CRT screen that emits light (monochrome or color) when struck by an electron beam. Each dot on the screen is actually a phosphor that glows for a period of time. See Persistence.
Picture tube: See Cathrode Ray Tube.
Pig tail: In a circuiting system, a short cable extending from a circuit box which has a female connector into which a lighting instrument is plugged.
Pin cushion: The inward or outward (curved) appearance of the edges of a display.
PING: Packet Internet Grouper. An internet utility used to determine whether a particular IP address is online. It is used to test and debug a network by sending out a packet and waiting for a response.
Pink Noise: Electronically generated noise that has equal energy per octave. Essentially has the same amount of energy per frequency in relation to what the human ear can hear. The amount of energy drops 3dB per octave. Compare with "White Noise."
PIP: Picture-In-Picture. Displaying a small picture within a larger picture by scaling down one of the images to make it smaller. Each picture requires a video source such as a camera, VCR, or channel selector. Consumer TV can use PIP for viewing two channels at the same time, for viewing taped video and a channel, etc. Videoconferencing uses PIP to display pictures from video sources at each participating site on each screen at the same time.
Pink noise: An audio test signal whose amplitude is inversely proportional to the frequency.
Pin out: An illustration or table that names signals, voltages, etc., that are on each pin of a connector or cable.
Pixel: Picture element. A pixel is a single point in a graphic image or screen. Pixels are arranged in rows and columns. See Pixel resolution.
Pixel clock: Dot clock. The pixel clock divides the incoming horizontal line of video into pixels. This pixel clock has to be stable (a very small amount of jitter) relative to the incoming video or the picture will not be stored correctly. The higher the frequency of the pixel clock, the more pixels that will appear across the screen (pixel resolution).
Pixel loss: A video problem in which picture information is missing, giving the appearance of specks in the image.
Pixel resolution: In computer graphics and video images, the pixel resolution is the number of pixels in the display. For example, a picture with 1,024 x 768 pixels is much sharper, or has higher resolution, than a picture with 640 x 480 pixels. The total number of pixels is the product of these two numbers.
Plane: In matrix switchers, a plane refers to all of the inputs and outputs of one signal. For example, the red plane would include all of the inputs and outputs for red signals; the blue plane would include all of the blue signals.
Plane breakaway: On matrix switchers, the ability to break one of the planes away from the others. Generally the video, sync, and audio planes will switch other the same way (i.e., have the same switching pattern). With plane breakaway, an individual plane can be set up to switch independently of the others.
Plane grouping or I/O grouping: When a number of independent planes on a matrix switcher are all grouped so that they switch in unison.
PLUGE: Picture Line Up Generation Equipment. This is the name of a test pattern that assists in properly setting picture black level. PLUGE can be part of many test patterns. The phrase and origination of the test signal are both credited to the British Broadcasting Company.
Plenum cable: Cable having a covering (jacket) that meets UL specifications for resistance to fire.
Point-to-point: A videoconference between two locations, like a telephone call. Also see Multipoint.
Polar Pattern: The graphic representation of the sensitivity of a microphone over all incident angles at a rated frequency.
Polarity: The positive and negative orientation of a signal. Polarity usually refers to the direction or to a level with respect to a reference (e.g. positive sync polarity means that sync occurs when the signal is going in the positive direction).
Pop: Microphone distortion caused by speaking certain hard consonants into a microphone placed so close to the mouth that the incoming sound filed overpowers the microphone coil.
Pop Filter: A wind screen that fits over the exterior of the diaphragm/microphone casing to reduce the pressure levels of plosive vocal sounds which cause a popping effect.
Popping: A microphone noise produced when the diaphragm is struck by a puff of air that is forced out of a speaker's or singer's mouth during pronunciation of plosive sounds (p, b, t).
Posterization: Special effect in which the picture is reduced to a small number of colors or luminance levels removing any fine gradations of color and brightness resulting in an oil painting effect.
Port: A connection for an input or output device. Typical ports found on a computer include serial, parallel, SCSI, disk drive, video, and keyboard ports.
Power (electrical): P. The dissipation of heat by passing a current through a resistance. Measured in watts [W], it is expressed by ohm's law from the three variables: voltage [E] current [I] and resistance [R]. That is, P = I2xR, or, P = E2/R or P = E x I.
Power Output: The rated power an amplifier can reproduce, in watts, in relation to load resistance and frequency.
Pre-amp: Pre-amplifier. An electronic circuit that raises a weak signal high enough to be fed into an amplifier.
Pre/Post: Method by which auxiliary effects can be independent or dependent on the main channel fader. If the send is "pre-fader," the main channel fader will not affect the aux send. If it is "post-fader," the main channel fader will affect the aux send.
Presentation device: A general term used to define a video projector or data monitor.
Pressure Zone Microphone: Microphones which carry with them small reflective surfaces which improve response.
Preview bus: A processor function allowing the operator to select any incoming video source for viewing prior to actual use.
Primary colors: Any set of colors from which other colors can be derived. In video, the primary colors are red, green, and blue. Equal amounts of red, green, and blue make white; the absence of all colors makes black.
Proc amp: Processing amplifier. An electronic device that stabilizes or rebuilds signals.
Processing amplifier: See Proc amp.
Production surround: Height adjustable velour drape, 3'; 6' tall used to enclose and mask front-of-house control positions from the audience.
Program bus: Similar to the preview bus in concept except that the resulting output is the final signal which goes live to screen
Progressive scan: See Non-interlaced.
Projection: The process of presenting visual media by light transmitted through an optics system to a viewing screen.
PROM: Programmable Read Only Memory. An electronic memory that does not lose its contents when power is removed, and that can be reprogrammed using a special PROM programmer ("burner"). See EPROM and EEPROM.
Protocol: A set of agreed-upon standards that define the format, order, timing, handshaking, and error checking method for data transfer between two pieces of equipment.
Proximity Effect: An inherent characteristic of certain directional microphones, resulting in a boost at the low-frequency response when a microphone is in close proximity to a source.
PZM: See "Pressure Zone Microphone."

Q

Q: A parameter that denotes the sharpness of a resonance. Also: as "Directivity Factor": Comparison of the sound power radiated directly ahead of a sound source to that radiated in all directions.
Quad standard: A term used for video products which are compatible with the following four standards: NTSC 3.58, NTSC 4.43, SECAM, and PAL.
Quantization: The process of sampling an analog waveform to convert its Q
Quantizing error: Inaccuracies in the digital representation of an analog signal. These errors occur as a result of limitations in the resolution of the digitizing process.
Quantizing noise: The noise (deviation of a signal from its original or correct value) that results from the quantization process. In serial digital video, it is a granular type of noise that occurs only in the presence of a signal.

R

Rack unit: In reference to product rack height, a unit is a universal measurement: 1.75 inches or 44 mm. 1U (Unit) high refers to 1.75 inches, 2U high refers to 3.5 inches, etc.
RAM: Random Access Memory. RAM is volatile memory that can be written to and read from. RAM is the working memory where active programs and data are stored. RAM normally loses its contents when power is removed. See PROM.
Raster: A raster is the series of scan lines that make up a TV picture or a computer's display. The term raster line is the same as scan line. All of the scan lines that make up a frame of video form a raster. Lines and rows of dots such as those on the illuminated face of a video screen. A matrix of pixels or the scan lines on a CRT.
RCA plug: A connector type most often used with line level audio signals and composite video.
Rear projection screen: A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front. Also see Front projection screen.
Rear screen projection: A presentation method in which the image is projected through a translucent screen toward the audience.
Reconstruction filter: A filter used to reduce aliasing and to soften the digital edges in an image. Without the reconstruction filter, images may have a "Moir� pattern" or "Jail Bar effect."
Rectifier: A diode that is used to change AC into pulsating DC.
Reflection: The return of a waveform from an obstruction in its path.
Reflections: With video signals, reflections can be caused by energy that is not absorbed by the load (or a termination) and is reflected and possibly combined with the original signal. Reflected signals can occur when the impedance does not match (as a result of wrong termination or mixing of cable= impedance). Some of the undesirable results of reflection include Y/C delays, color smearing, ringing on luma (but not on color), and ghosts.
Refraction: The bending of a waveform as it passes from one medium to another, or as it experiences a change (i.e. temperature) within the medium.
Relay: A device that acts like a switch and is controlled by a current. The relay switch contacts and then controls another circuit to pass a signal. Most relays are either solid state or electromagnetic.
Remote control: A wired or wireless device for controlling the function of another device at a distance. Also see IR remote.
Resistance: The opposition to the flow of electric current. See Power and ohm.
Resistor: An electrical component that limits the flow of current via resistance or impedance. It allows a specific amount of current to flow, as determined by the voltage applied to the resistor.
Resonance: Certain systems, whether they are the sounding board of a grand piano or the air cavities within a microphone or in an electrical circuit, have a natural frequency at which they vibrate. When the movement of air or vibrations borne by the structure hit this frequency the system mass operates in "sympathy" and the system is said to be in resonance. Resonances reinforce certain frequencies because they are in sympathetic vibration with them.
Resolution: The density of lines or dots that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly, it is the bandwidth. A sharp, clear picture has high resolution. Also see Resolution (horizontal) and Resolution (vertical).
Resolution (horizontal): The amount of detail in a horizontal direction in a video image. It is expressed as the number of distinct vertical lines, alternately black and white, that can be seen in the width of the picture. This information is usually derived from observation of the vertical wedge of the test pattern. Horizontal resolution depends on the high-frequency amplitude and phase response of the pick-up equipment, as well as the transmission medium and the monitor itself.
Resolution (vertical): The amount of resolvable detail in a vertical direction in a video image. It is expressed as the number of distinct horizontal lines, alternately black and white, that can be seen in a test pattern. Vertical resolution is primarily determined by the number of horizontal scanning lines in a frame.
Response, flat: The way in which a microphone de-emphasizes or accentuates particular frequencies. A flat response is an even response and usually the most desirable, although some high frequency lift for vocals and strings is also popular.
Retrace: During the scanning of a picture onto a screen, scan lines are produced from left to right. Before scanning the next line, the electron beam just get back to the left side of the screen. This is called retrace. The beam must be turned off (blanked) during retrace time. (See horizontal blanking and vertical blanking.) A retrace problem could appear as missing video information on the left side of the screen.
Retrace time: The time required to move the scanning beam from the right side to the left side of the screen.
Retro: A rear-projection video display.
Return loss: A measure of reflected energy in decibels at a specific frequency and cable length.
Reverberation: The way in which a sound bounces around an auditorium after its original source has been cut off. The amount depends on auditorium shape, strength of signal, and how much absorption is present.
Reverberation Time: The time required for the stored or reverberant sound to decrease by 60 dB.
RF: Radio frequency. A range of frequencies used for electromagnetic transmission (e.g., radio and TV).
RF adapter: A device that allows video and audio signals from a video tape recorder (VTR) or computer to be shown on a standard TV receiver. This device produces comparatively poor resolution and picture quality. Also called "RF converter."
RF control: A medium of remote control from which signals are sent to the controlled equipment via data pulses modulated on an RF carrier signal.
RFI: Radio Frequency Interference. High frequency interference from transmissions such as telephones, microwaves, and television stations.
RGB: Red, green, and blue. The chroma information in a video signal. The basic components of the color television system. They are also the primary colors of light in the additive color process. Also see Subtractive color.
RGBHV: Red, Green, Blue, Horizontal, and Vertical Sync. A five-wire signal where the red, green, and blue video signals, as well as the horizontal and vertical sync signals are on its own conductor.
RGBS: The red, blue, and green chroma information in a video signal, with a separate channel for the sync signal.
RGsB: Red, Green, Blue, and Sync on Green. A three-wire signal with separate red, green, and blue video signals with the sync (horizontal and vertical) on the green signal.
RGB Distribution amplifier: A RGB DA accepts the input of one set of 5 wire, and distributes (splits) the signal to between 2 & 6 outputs, lightly amplifying each output to return each to its original signal strength.
RGB Switcher: A switcher containing 2 format scalers that is capable of seamless transitioning between multiple formats such as RGB, Component & Composite, with the final output being RGB HV. The Folsom SPR2000 is an example of this.
Ringing: In video, closely spaced repeated ghosts of a vertical or diagonal edge where dark changes to light or vice versa, going from left to right caused by the electron beam upon changing from dark to light or vice versa instead of changing quickly to the desired intensity and staying there, overshoots and undershoots a few times
Rise time: The time required for a signal to go from 10% to 90% of its maximum amplitude level.
RJ: Registered Jack. A type of modular jack that is similar to those used with telephones. Examples: RJ-11 = 4 or 6 wire module, RJ-45 = 8-wire module.
RJ-45: Registered Jack-45. A connector similar to a telephone connector that holds up to eight wires, used for connecting Ethernet devices.
ROM: Read Only Memory. Permanent memory that can only be loaded once, normally by the manufacturer. Contents may not be altered or removed. Also see PROM, EPROM, and EEPROM.
Room camera: In videoconferencing, this is the main camera in the room; there may be additional cameras in the room.
RMS: The output of the amplifier taken as an average-; root mean square.
RS-170A: EIA technical standard NTSC color TV. A video standard that ensures proper synchronization of video signals and components.
RS-232: An Electronic Industries Association (EIA) serial digital interface standard specifying the characteristics of the communication path between two devices using either DB-9 or DB-25 connectors. This standard is used for relatively short-range communications and does not specify balanced control lines. RS-232 is a serial control standard with a set number of conductors, data rate, word length, and type of connector to be used. The standard specifies component connection standards with regard to the computer interface. It is also called RS-232-C, which is the third version of the RS-232 standard, and is functionally identical to the CCITT V.24 standard.
RS-330: An EIA technical standard that provides details for industrial closed-circuit television (CCTV).
RS-422: An EIA serial digital interface standard that specifies the electrical characteristics of balanced (differential) voltage, digital interface circuits. This standard is usable over longer distances than RS-232. This signal governs the asynchronous transmission of computer data at speeds of up to 920,000 bits per second. It is also used as the serial port standard for Macintosh computers.

S

Safe action area: This amounts to about 90% of the total picture area, is symmetrically located inside of the picture border and is designated as the area of the picture that is "safe" to put action that the viewer needs to see.
Safe title area: Generally, the center 80% of the entire overscanned video image area or that area which will display legible titles regardless of how a TV monitor is adjusted.
Sample: A digital "snippet" of a sound, which can be triggered by a MIDI keyboard, such as; a drum sound, orchestral sound or vocal phrase.
Sample rate: When audio is digitized, the sampling rate is the number of "pictures taken" in a second, higher sample rate means that the resolution of the recording is high, thus very "accurate". Most common sample rates in professional recording are 44.1Khz and 48Khz.
Saturation: Chroma, chroma gain. The intensity of the color, or the extent to which a given color in any image is free from white. The less white in a color, the truer the color, or the greater its saturation. On a display device, the color control adjusts the saturation. Not to be confused with the brightness, saturation is the amount of pigment in a color, and not the intensity. Low saturation is like adding white to the color. For example, a low-saturated red looks pink.
SC: Subcarrier. The modulation sidebands of the color subcarrier containing the R-Y and B-Y information. A secondary signal containing additional information that is added to a main signal.
Scaler: A device that takes a standard video signal, decodes it, and uses advanced digital signal processing technology to scale the image to the optimal or native resolution of a display device.
Scaling: Scaling is changing the size of an image without changing its shape. Scaling may be required when the image size does not fit the display device. An example of scaling down would be to take a 640 x 480 resolution TV image and display it as a smaller picture on the same screen so that multiple pictures can be shown at the same time (such as with picture-in-picture, PIP). If the original image is scaled down to a resolution of 320 x 240, this is 1/4 of the original size, allowing four pictures to be shown on the same screen at the same time. An example of scaling up would be to take a lower resolution image (800 x 600 = 480,000 pixels) and display it on a higher resolution (1024 x 768 = 786,432 pixels) device. The number of pixels is the product of the two numbers. This means that pixels must be created. There are many different methods for image scaling, and some produce better results than others.
Scan: (1) In video, to move an electron beam across the raster in a camera or monitor. (2) To feed visual information into a computer by means of an optical device called a scanner.
Scan converter: Also called "video converter" or "TV converter," a scan converter is a device that changes the scan rate of a source video signal to fit the needs of a display device. Examples: computer-video to NTSC (TV), or NTSC to computer-video.
Scan doubler: A device used to change composite interlaced video to non-interlaced component video, thereby increasing brightness and picture quality. Also called "line doubler."
Scan-doubling: The process of making the scan lines less visible by doubling the number of lines and filling in the blank spaces. Also called "line-doubling."
SC/H phase: Subcarrier to Horizontal phase. In NTSC video, this is the phase relationship of the subcarrier to the leading edge of horizontal sync. SC/H phase is correct when the zero crossing of subcarrier is aligned with the 50% point of the leading edge of sync. In PAL video, the SC/H phase is defined as the phase of the EU component of the color burst extrapolated to the half amplitude point of the leading edge of the synchronizing pulse of line 1 of field 1.
Scrolling: The displayed image (or interfering noise on the image) rolling constantly on the screen.
Screen surfaces: glass beaded; A glass beaded screen surface has the ability to achieve a higher gain by reflecting more of the projected light back along the projection axis. glass beads impregnated in the screen's surface provide additional reflectance providing a screen surface for vibrant, life-like color reproduction at moderate viewing angles.
Screen surfaces: high power; The multi-layered surface provides the high reflectivity of a glass beaded surface with the unique ability to clean the surface when required. It's smooth textured surface provides the highest gain of all typed of screen surfaces with a moderate viewing angle.
Screen surfaces: lenticular -A screen surface characterized by a lens-like embosses and sliver or aluminized surface to reflect maximum light over a wide horizontal and narrow vertical angle.
Screen surfaces: matte white; The most versatile screen surface for situations where ambient light is controllable. It's surface evenly distributes light over a wide viewing area. colors remain bright and life-like, with no shift in hue
Scrim: One of many types of woven gauze-like scenic materials, a scrim will appear as opaque when lit primarily from in front, or can become transparent when objects are lit behind it.
SCSI: Small Computer System Interface. Pronounced "skuzzy." An industry-standard input/output bus for peripheral computer devices, such as hard disks and CD-ROM drives. A standard peripheral bus on Mac computers. Improvements, such as the number of data lines and speed, have been made to the original SCSI to become SCSI-2 and SCSI-3.
SDI: Serial Digital Interface. The standard based on a 270 Mbps transfer rate. This is a 10-bit, scrambled, polarity independent interface with common scrambling for both component ITU-R 601 and composite digital video and four channels of (embedded) digital audio.
SDTV: Standard digital television. A serial digital format whose samples and timing are derived from 4:2:2 digital component video sources. The main difference between existing digital component video and SDTV is an MPEG-2 compression step to reduce the channel bandwidth.
Seamless switching: A switcher that uses advanced signal processing to switch between sources to either dissolve or switch without any black, glitch or other artifacts. The switcher waits until the vertical interval to switch. This avoids a glitch (temporary scrambling) which normally is seen when switching between sources.
Search Engine: an internet portal that permits a user to search throughout the world wide web of webpages for particular words, terms or nomenclature. Popular search engines include Google, MSN, Yahoo, AOL and AllTheWeb.
SECAM: Sequential Couleur Avec M�moire. Translated as sequential color with memory. A composite color transmission system that potentially eliminates a need for both a color and hue control on the monitor. One of the color difference signals is transmitted on one line and the second is transmitted on the second line. Memory is required to obtain both color difference signals for color decoding. This system is used in France, Africa, Asia, Russia, Saudi Arabia, and many Eastern European countries. It is similar to PAL but produces color signals in a different manner. SECAM uses 625 horizontal scan lines, 50 fields per second (625/50).
SEG: Special Effects Generator. A video-mixing device that allows switching among several cameras and a variety of special effects such as dissolves, fades, wipes, and inserts.
Sepia tone: A process used in photography to generate a brownish tone in pictures giving them an "antique" appearance, that can be electronically adapted for video production where a black and white image can be colored in sepia.
Serial data: A way to transfer information by breaking the characters of a word into bits, which are then transmitted sequentially along a single line. Compare to parallel, which uses more than one line.
Serial port: An input/output connection on the computer that allows it to communicate with other devices in a serial fashion-data bits flowing on a single pair of wires. The serial port is used with RS-232 protocol.
Serration pulse: A vertical synchronizing pulse divided into a number of small pulses, each acting for the duration of half a line in a television system. Serration pulses are used to keep the horizontal oscillator synchronized during the vertical sync pulse interval.
Shadow mask: A metal plate with holes or vertical lines that is used to determine exactly where the electron beam strikes the CRT screen.
Sharpness: The definition of the edges of an image. Also see Peaking.
Sharpness control: Same as Peaking control.
Shield: In an audio cable, a conductive cylinder around one or more center conductors that protects against unwanted electrostatic fields that could induce a signal, heard as a hum or buzz, across the conductors of the cable.
Shin buster: A luminaire that is placed as close to the stage floor as possible, focused such that no light shines on the floor giving the illusion that the subject is floating.
Shock Mounting: Any mounting or suspension system that mechanically isolates equipment from unwanted vibration.
Sibilance: Emphasis of s, sh, or ch sounds.
Signal loss: A video problem that shows up as a faint picture for lack of video information.
Signal-to-Noise Ratio: The ratio, usually expressed in decibels, of the average signal (recorded or processed) to the background noise (caused by the electronic circuits).
Single-ended: An unbalanced circuit where one side of the circuit or transmission line is grounded. Single-ended audio is unbalanced audio.
Skew: Refers to the timing difference which occurs when electrical signals which are traveling over different pairs of cables reach their destinations at different times. The different arrival times of the signals may present a problem when simultaneous arrival with no delay is required.
SMTP: Simple Mail Transfer Protocol. Internet standard for email exchange across systems/networks on the Internet.
Smearing: A video problem where objects such as horizontal bars extend past their boundaries. Also called "over-peaking."
SMPTE: Society of Motion Picture and Television Engineers. A global organization, based in the United States, that sets standards for baseband visual communications. This includes film as well as video standards.
SMPTE pattern: The video test pattern consisting of color, black, and white bands used as a standard for setting up video equipment.
Snake: A moveable patch panel with cable. Usually, a box with many XLR connectors on it that terminates in a multipair cable of undetermined length, which then terminates into a fan-out of corresponding connectors. Basically, many microphone cables rolled into one.
SNMP: Simple Network Management Protocol. Allows for management of network devices with administration software.
S/N ratio: Signal-to-Noise ratio. The ratio is measured in decibels, between the audio or video signal level and that of the noise accompanying the signal. The higher the S/N ratio, the better the quality of the sound or picture.
Snow: Visual noise in a video picture giving the appearance of white flecks of snow.
Software: The programs used to instruct a processor and its peripheral equipment to perform prescribed operations.
Sound Pressure Levels: The measurement of what sound we hear expressed in decibels in comparison to a zero level.
Spanset: A loop of nylon webbing wrapped around load bearing structures at the points to which it will be rigged.
Spatial resolution: Spatial resolution is a measurement of the total number of pixels displayed in an entire image, usually noted in terms of horizontal by vertical (640 x 480).
Speakon: A connector designed by the Swiss company Neutrik specifically for use with speaker-levels. Available in two versions: four pole and eight pole. The chassis (amplifier or speaker) is always a male version; the cable ends are always female.
Speed: The speed relates to the air temperature which should always be quoted. The speed of sound is 331.45 m/sec. (1087.42 ft/sec) at 0 degrees Celsius.
SPL: see sound pressure level
Split screen: A video effect where portions of images from two sources divide the screen.
Static mesh: A basic de-interlacing process scalers use for video content that contains no movement. This type of processing results in a sharp image with crisp details but will cause images to tear when motion occurs.
Steadicam: Patented, Oscar-winning camera stabilizing device. Worn like a (very heavy) vest, the Steadicam keeps camera movements smooth anywhere a heavily-laden person can walk. Trademark of Cinema Products Corp.
Stereo: A process of using separate audio signals on separate channels for the left and right audio, thereby giving depth, or dimension to the sound.
Stereo Pair: A coincident pair of microphones with their axes of maximum response at an angle of 90 degrees.
Strike: In the audio/video industry, strike is a term for taking down an installation, for example at a show.
Studio configuration: Servo controls for a video camera that allow the operator to adjust the zoom and focus remotely from a comfortable position behind the camera, instead of physically touching the lens
Subnet mask: The method used for splitting IP networks into a series of subgroups or subnets. The mask is a binary pattern that is matched up with the IP address to turn part of the host ID address field into a field for subnets.
Subtractive color process: Process used in color printing. Mixing cyan, magenta, yellow, and black (CMYK) produces millions of desired colors. Examples: 0% of C, Y, M and K = white (no ink); 100% of C and M = red; 100% C, Y, and M = process black. Also see Additive color (RGB).
Subwoofer: A specific type of speaker dedicated to reproducing very very low frequency sounds. Usually a big cabinet located on the floor [placing the cabinet on the floor mechanically couples the low-frequency vibrations to the floor, enhancing the effectiveness.]
Super: Short for "superimpose." A visual effect in which one image is placed "atop" or "in front of" another, as when a person's name appears over their picture during an interview.
Superimposition: Placing one image over another so that both may be seen at the same time. The effect can be achieved in many ways: by more than one exposure on a single piece of film, by multiple printing, or by registered projection. Abbreviated "super."
SVGA: Super Video Graphics Array. A term used to denote resolutions higher than VGA (640 x 480). SVGA computer graphics cards have a resolution of 800 x 600 (480,000 pixels) but may be able to output resolutions of up to 1280 x 1024 and 16 million colors.
S-VHS: Super-Video Home System. A high band video recording process for VHS that increases the picture quality and resolution capability. Also see S-video.
S-video: A composite video signal separated into the luma ("Y" is for luma, or black and white information; brightness) and the chroma ("C" is an abbreviation for chroma, or color information).S-Video (also called Y/C or component video) is carried on cables that end in 4-pin Mini-DIN connectors. A video signal transmitted according to this standard separates color and brightness into two separate channels. This makes for a sharper picture image, with less granularity, on the receiving device. Y/C signals use two separate video signals. The luminance (Y) is the black & white portion, providing brightness information. The chrominance, or chroma (C) is the color portion, providing hue and saturation information. (Three-wire component video signal is split into three parts; black and white information (Y), and two colour difference signals (Pb and Pr). The S-Video connection keeps the all-important black and white (Y) information separate, and combines the colour difference signals into a single colour signal (C). Instead of three separate signals, there are two separate signals.)
Switched 56: An older system of digital telephone lines used in North America, which is being replaced by ISDN. Also see ISDN.
Switcher: A device that allows a selection between more than one source, such as video cameras, VCRs, etc. In audio/video, switchers are a means of connecting an input source to an output device or a system. Also see Matrix switcher. (2) A term often used to describe a special effects generator; a unit that allows the operator to switch between video camera signals. Switchers are often used in industrial or security applications to switch between video cameras that view certain areas for display on a monitor, or system of display devices. These kinds of switchers do not have sync generators.
SXGA: Super Extended Graphics Array. A graphics standard with a resolution of 1280 x 1024 (1,310,720 pixels). This exceeds XGA (1024 x 768, at 786,432 pixels).
Sync: Synchronization. In video, sync is a means of controlling when things happen with respect to other things. This is accomplished with timing pulses to ensure that each step in a process occurs at exactly the right time. For example, horizontal sync determines exactly when to begin each horizontal line (sweep) of the electron beam. Vertical sync determines when to bring the electron beam to the top left of the screen to start a new field. There are many other types of sync in a video system. Also called "sync signal" or "sync pulse."
Sync generator: A circuit that produces sync impulses used to control the time when certain events happen electronically.
Sync-on-green switch: A switch on certain devices and interfaces that allows the sync signal to be added to the green channel as required.
Sync polarity: (1) A circuit can be designed to operate on the positive-going or negative-going part of the sync pulse. Some equipment has a sync polarity option switch to allow selecting which edge (plus or minus) to trigger on. (2) This refers to the duty cycle of the sync signal. A positive polarity sync signal is low most of the time, and high for a short time. Negative polarity sync is high most of the time and low for a short time.
Sync termination adapter: See LSTA, ASTA, and LSCA.
System Switcher: A switching device that also communicates with other components in a system, such as a projector. By having communications between a switcher and a projector, the projector's remote control can command the switcher to change inputs. Also, the projector can be turned on/off by a command from the switcher.

T

t.120: CCITT standard for digital computer data interchange videoconfer-encing.
Talent: A term used to refer to on-camera subjects in a video production.
Tally lamp: A signal lamp or LED installed on a video camera which informs performers and crew members that the camera is currently live.
Teleprompter: A device for displaying large, readable text on a partially transparent screen for the talent to reference to for their script.
Talkback: On a mixer, the input (usually located on the fascia) that enables the sound engineer to yell at people through the loudspeaker system. Some mixers have comprehensive talkback systems whereby the engineer can address any of the aux sends or any of the groups individually and yell at individual groups of people through individual loudspeaker systems.
TCP: Transmission Control Protocol. A method (protocol) used along with the Internet Protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called a packet) that a message is divided into for efficient routing through the Internet.
TCP/IP: Transmission Control Protocol/Internet Protocol. Based on the IETF standard RFC793: TCP is a reliable, connection-oriented protocol that first establishes a connection between the two systems that will exchange data. When an application sends a message via TCP for transmission, TCP breaks the message into packets, sized appropriately for the network. TCP provides the flow control (to prevent overrunning the receiver) and congestion control (to prevent overwhelming the capacity of the network). For Ethernet networks, the maximum packet size is 1518 bytes. TCP uses the IP protocol to address and send the packets. The IP protocol uses three key parameters: the IP address, subnet mask, and default gateway.
Telecommunications: An electronic method of transmitting information from one location to another over a telephone network.
Teleconferencing: A meeting between people at two or more locations who can communicate by audio and/or visual devices often via telephone and/or closed-circuit television. Also see Videoconferencing.
Temporal: Relating to the sequence of time or to a particular time.
Terminal: A device typically having a keyboard and display that is capable of sending text to and receiving text from another device, a network, etc.
Termination: A load or impedance at the end of a cable or signal line used to match the impedance of the equipment that generated the signal. The impedance absorbs signal energy to prevent signal reflections from going back toward the source. For video signals, termination impedance is typically 75 ohms; for sync signals, it is usually 510 ohms.
Terminator: A device that provides termination for a signal line or several signal lines at the end of a cable. Usually a close-tolerance resistor for each signal, a terminator is often mounted in its own enclosed connector, making it easy to install.
TFT: Thin Film Transistor LCD panel. A type of LCD flat panel display screen in which each pixel is controlled by one to four transistors. The TFT technology provides the best resolution of all the flat panel techniques, but it is also the most expensive. TFT screens are sometimes called active matrix LCDs.
THD: Total Harmonic Distortion. The amount of internally generated noise in a receiver which is a variation from the ideal sound wave. Since the perfect audio wave is physically impossible, the variation from the ideal wave is the percentage referred to as THD.
Threshold of pain: The minimum sound pressure level of a pure tone which causes a sensation of pain in the ear. About 140dB SPL.
Throw: The distance from projector lens to screen.
THX: The Tomlinson Holman Experiment is standard specifications for audio designed to provide consistent audio reproduction as close as possible to what was originally intended. Established by Lucasfilm
Time base corrector: Video tape recorder (VTR) playback circuitry used to smooth out the wavering edges of a video image.
Time base error: Slight errors in the line-to-line position of video information that occur between recording and playback. At the time of playback, these appear as serrations, tending to make the edges of the image waver.
Time base generator: A sync generator which puts a clock signal on the video tape to refer to for precise horizontal lock-up of an image.
Time code: A digital or binary code used to label each frame of a video signal. This is very useful for editing the video since the time code is in the form of hours, minutes, seconds, and frames.
Tint: A relative measure of the amount of white in a given color. Also see Hue.
TMDS: Transition Minimized Differential Signaling. An all-digital video transmission standard developed by Silicon Image, Inc. The standard is limited to 5 meters or 15 feet. Silicon Image markets this standard as PanelLink�.
Toggle: To switch between alternate states. For example, between on and off, or caps and lower case.
Toggle switch: A switch having two positions or two states. When an activating force is applied, the state changes.
Touch panel: A control panel with a flat surface (usually with graphic divisions or buttons) that functions as a switch or control. Also called a "touch screen."
TP: Twisted Pair. Cable that uses small twisted pairs of wires in a common jacket/sheath to transmit/receive network/telephone signals; can be either shielded (STP) or unshielded (UTP).
Transducer: Any device which converts an input signal into an output signal of a different energy form (i.e. acoustic to electric). A microphone, loudspeaker, etc.
Transistor: A solid-state amplifying device consisting of a crystal of germanium or silicon with carefully selected impurities.
Tri-level sync: A sync level scheme developed for HDTV which has the sync line first going low, then transitions high while going through the reference voltage level, then drops back down to the reference voltage. The transition of the positive-going sync signal through the reference voltage is the sync trigger.
TTL: Transistor-to-Transistor Logic. A digital signal, usually 4-5 volts peak-to peak with a distance limitation is 6-10 feet (1.8-3.0 meters). Signal splitting is acceptable. TTL signals are either on or off, and are characteristic of low resolution computers (CGA/EGA).
Tweak: To adjust or fine-tune.
Tweeker: A small screwdriver for making sensitive adjustments to audio/visual and other electronic equipment.

U

UHF: Ultra High Frequency. A television broadcast frequency range between 300 and 3000 MHz, on channels 14 through 83. Also the name for a type of connector used for video cables.
UL � -Underwriters Laboratories: When marked by the UL symbol, a product has been tested and evaluated according to nationally recognized safety standards with regard to fire, electric shock, and related safety hazards. There is also a UL for Canada, sometimes called CUL, and a UL recognized component with its own symbol, resembling a backward "UR."
Unbalanced audio: An audio output where one of the two output terminals is at ground potential.
Underscan: A decreasing of the raster size (H and V) so that all four edges of the picture are visible on the screen. Underscanning allows viewing of skew and tracking which would not be visible in normal (overscanned) mode. It is also helpful when aligning test charts to be certain they touch all four corners of the raster. Likewise, when checking the alignment of multiplexer images from a film chain, underscan allows proper framing of the projected image going into the video camera.
Unidirectional Polar Pattern: see "Cardioid."
UPS: Uninterruptible Power Supply. A power supply that continues to provide voltage for a limited time after the main power is off (fails).
URL: Uniform Resource Locator. This is the address that lets a resource on the internet be identified, located, and accessed.
USB: Universal Serial Bus. USB was developed by seven PC and telecom industry leaders (Compaq, DEC, IBM, Intel, Microsoft, NEC, and Northern Telecom). The goal was easy plug-and-play expansion outside the box, requiring no additional circuit cards. Up to 127 external computer devices may be added through a USB hub, which may be conveniently located in a keyboard or monitor. USB devices can be attached/detached without removing computer power. The number of devices being designed for USB continues to grow, from keyboards, mice, and printers to scanners, digital cameras, and ZIP drives.
UV: Ultraviolet. Light/heat rays that have a shorter wavelength (and higher frequency) than those in the visible spectrum. UV rays are ordinarily filtered or blocked to prevent eye damage and dye fading.
UXGA: Ultra Extended Graphic Array. 1600 x 1200. A UXGA dispay has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.

V

V

(1) Vertical (as in RGBHV), or the vertical sync connector on a panel. This is used when the sync is separated into horizontal and vertical components. (2) In electrical specifications, "V" is the abbreviation for volts.

VAR

Value Added Re-seller. A party who purchases a product, adds something to it, such as hardware or software, and then sells it as a package.

Variable level control

This is a variable voltage level control similar to a contrast control on a data monitor. The level control increases or decreases the levels of red, green, and blue simultaneously, thus not affecting the adjusted grayscale of the monitor or projector.

VCA

Voltage Controlled Amplifier. Used in a mixer: instead of the signal being directly manipulated by the fader (and being subject to inconsistencies in the fader itself), the fader controls a voltage that corresponds to a certain sound level. Makes for cleaner sound since the fader quality doesn't have to be as clean. It's like a light board — the fader tells the dimmers what to do. Same principle. VCAs can often be assigned to different faders at different times; see console instruction manual for more information.

VCR

Generally defined as Video Cassette Recorder. In Europe, however, VCR is a trademark for a particular video format developed by Philips in The Netherlands.

Vectorscope

A special oscilloscope used in video systems to measure chroma.

Vertical blanking

Turning off the electron beam in a CRT during the time the beam returns from the bottom of the screen to the top after scanning each field of a picture. If vertical blanking does not occur, a diagonal retrace line will display from lower right to upper left of the screen. Also see Retrace.

Vertical blanking interval

The blanking time at the beginning of each field. It contains equalizing pulses and vertical sync pulses.

Vertical centering control

Adjusting the vertical centering control one way shifts the displayed image toward the bottom of the screen and the other way shifts the displayed image to the top of the screen. Also called "vertical shift," or "vertical position."

Vertical double images

A video problem when the display is split across the middle with two identical (squeezed) images on the top and bottom of the screen.

Vertical filtering

This is a feature in some scan converters that controls the number of lines to process, as well as the way in which they are processed. This affects the sharpness vs. flicker of the scan-converted picture.

Vertical interval

The period of time between the end of one video field and the beginning of the next. During this time, the electron beam in a camera, monitor, or projector is turned off (blanked) while it returns from the bottom of the screen to the top, to begin scanning the next field. The portion of the video signal that represents this time period may also be called the vertical interval.

Vertical resolution

Also known as "vertical definition." The number of distinct horizontal lines, alternately black and white, that can be seen in a TV image. Vertical resolution is fixed by the number of horizontal lines used in scanning.

Vertical sync pulse width switch

A switch on some interfaces that increases the width of the vertical sync pulse, for example from 180 microseconds to 500 microseconds.

Vertical temporal

A scaling process for video content that contains movement. This type of scaling process employs an averaging technique to merge the odd and even fields of video into a single frame. This type of processing treats the entire picture as if in motion and results in less motion artifacts. Disadvantages include blurring and loss of vertical resolution.

VESA

Video Electronics Standards Association. A nonprofit member organization dedicated to facilitating and promoting personal computer graphics through improved standards for the benefit of the end-user. www.vesa.org

VGA

Video Graphics Array. Introduced by IBM in 1987, VGA is an analog signal with TTL level separate horizontal and vertical sync. The video outputs to a 15-pin HD connector and has a horizontal scan frequency of 31.5 kHz and vertical frequency of 70 Hz (Mode 1, 2) and 60 Hz (Mode 3). The signal is non-interlaced in modes 1, 2, 3 and interlaced when using the 8514/A card (35.5 kHz, 86 Hz) in mode 4. It has a pixel by line resolution of 640 x 480 with a color palette of 16/256,000.

VHF

Very High Frequency. Television broadcast range between 30 and 300 MHz, on channels 2 through 13. The FM radio band is between channels 6 and 7 (88 to 108 MHz).

Video

Refers generally to any method using videotape or television technology to produce an image.

Video amplifier

A low-pass amplifier with a bandwidth of 2 to 10 MHz, used to strengthen the video signal for TV transmission and reception.

Video card

A circuit board that is usually mounted inside the computer that generates signals necessary to drive or control a specific type of monitor.

Video connector

The connector on the video card or computer's graphics output that is connected to the video input on the local monitor.

Video Conferencing:

H.320 Videoconferencing on ISDN: The H.320 standard has been in place for a decade and videoconferencing today is most commonly implemented on ISDN, providing high quality because its synchronous nature with very low delay and delay variation. ISDN is able to implement videoconferencing at transmission rates from 64Kbps up to 2Mbps. At 128Kbps, videoconferencing on ISDN is only of marginal quality and cannot really be considered suitable for most business uses. ISDN-based videoconferencing at 384Kbps can be considered the baseline of business quality videoconferencing and provides a high quality transmission of videoconferencing. The implementation of ISDN at speeds of 384Kbps and above is costly and a complex undertaking. Three 128Kbps Basic Rate ISDN (BRI) interfaces must be used for every videoconferencing device. Using a device called an IMUX, these three BRI lines must be bonded together to form a single communications channel. This standard is used today by about 90% of all videoconferencing users.
H.323 Videoconferencing on Frame Based Networks: The standard H.323 was designed for videoconferencing on frame based networks (Ethernet, Token Ring, FDDI, ATM) using TCP/IP protocol. Today H.323 normally does not provide as high quality videoconferencing as H.320.
H.310 Videoconferencing: H.310 is a MPEG-based videoconferencing and is different from H.320 and H.323. A two-way MPEG2 videoconferencing at up to 15Mbps (with a latency of about 150ms) is like watching TV! It requires up to 15Mbps of bandwidth and the hardware costs significantly more.

Video distribution amplifier

An amplifier for strengthening the video signal so that it can be supplied to a number of video monitors at the same time.

Video gain

The increase in the amplitude of a video signal.

Video projector

A device that projects a video image onto a presentation surface.

Video standards

See NTSC, PAL, and SECAM.

Videoconferencing

Conducting a live conference between two or more locations using video cameras, microphones, and video monitors. The participants can be seen as well as heard. Referred to as a virtual conference room. Also see Teleconferencing.

Video-follow-audio

In videoconferencing, when the video source switches automatically to show the person speaking, regardless of the location.

VHS

Video Home System. The half-inch videocassette format originated and developed by JVC and adopted by a number of different manufacturers. Not compatible with the Beta format, which also uses half-inch tape but differs electronically.

Virtual conference room

See videoconferencing.

Virtual memory

The process of increasing the apparent size of a computer's random-access memory (RAM) by using a section of the hard disk storage as an extension of RAM.

VITC

Ver tical Interval Time Code. Timecode information stored on specific scan lines during the vertical blanking interval.

VLB

Video Loopback. A feature in some switchers that allows a video signal to exit to another device, such as a decoder or scan doubler, and the output of that device is then used as another input to the same switcher. This allows any switcher input to use the decoder or scan doubler, saving the cost of buying separate units.

Volt

The potential difference or electromotive force that will cause current of one ampere to flow through the resistance of one ohm. Symbolized by "V."

Voltage

The potential difference or electromotive force expressed in volts. Also see Volt.

VTG

Video Test Generator. A device that generates video test patterns at scan rates that simulate most popular applications.

VU meter

Volume Unit meter. For audio systems or recorders, a VU meter is a device that indicates the relative levels of the audio being recorded or played. It is usually calibrated to show a maximum recording level to avoid tape saturation and distortion.

W

WAN: Wide Area Network. Long-distance networks using various transmission technologies such as the Internet, frame relay/atm, fiber, or ISDN.
Watt: A unit of electrical power used to indicate the rate of energy produced or consumed by an electrical device. One watt is one joule of energy per second. Also see Power.
Waveform: A display of a signal (on an oscilloscope) that shows the magnitude of current or voltage signal with respect to time. By displaying the waveform of a signal on an oscilloscope, the time between cycles can be measured and its frequency can be calculated.
Waveform monitor: A special oscilloscope used to display and analyze electrical (voltage or current) signals.
Wavelength: The distance from one peak to the next between identical points in adjacent waves of electromagnetic signals propagated in space or along a wire. Wavelength is usually specified in meters, centimeters, or millimeters. In the case of infrared, visible light, ultraviolet, and gamma radiation, the wavelength is usually specified in nanometers (10-9 meter) or Angstroms (10-10meter). Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength.
White: The lightest visible surface created by a reflection of all colored light.
White Balance: A setting and adjustment made on video cameras to ensure pure white and proper colour reproduction accurate to the eye when replayed or displayed in comparison to the original or true representation.
White level: In television, the signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.
White noise: Noise with random amplitude (strength) over a wide frequency range. Used to test speakers for resonance and sensitivity. Low levels of white noise can be used to cover up other random noises, for example, in an open office environment. A full audio spectrum signal with the same energy level at all frequencies. Compare with "Pink Noise."
Wideband: A relative term indicating a high bandwidth.
Width: The size of the video display area in a horizontal direction.
Wipe: A visual transition between images during which the edge of one image moves across the screen revealing the next image.
Workstation: A type of computer used in design or development work, such as engineering and CAD, requiring a moderate amount of computing power and high-resolution graphics.
Wrap-around: A video problem that occurs when the left picture information is displayed on the right side of the screen and the right picture information is displayed on the left side of the screen, separated by a vertical bar.
WSXGA: WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels, respectively, that are used to compose the image delivered by the projector.
WWW: World Wide Web. An international network of subscriber sites where information in the form of text and/or graphics is made available to computer users (Web site visitors).
WXGA: WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels, respectively, that are used to compose the image delivered by the projector.

X

XGA: Extended Graphics Array card. IBM's graphics standard that includes VGA and extended resolutions up to 1024 x 768 (interlaced 35 kHz). This card uses a 15-pin HD VGA-style connector.
XGA-2: Extended Graphics Array card, 2nd generation. Capable of scanning from 31 to 68 kHz and resolutions up to 1600 x 1200 pixels, this card uses a 15-pin HD VGA-style connector.
XLR connector: A type of audio connector featuring three leads: two for the signal and one for overall system grounding. A secure connector often found on high quality audio and video equipment. Also called a" cannon connector." The origin of the XLR connector was the Cannon X Series connector. It was fitting the demands of the audio community except the missing latch. Cannon rearranged the pins and added a latch. The new connector was called Cannon XL Series (X Series with Latch). Later the female version was changed to put the contacts in a resilient rubber compound. The connector was then called Cannon XLR Series. This connector soon became the industry's standard and nearly every connector manufacturer copied the Cannon connector. It became a AES standard in 1982 with the pin assignment: 1: shield/ground, 2: hot pin, 3: cold pin. It has needed a long period of time until the pin 2 / pin 3 confusion was finished (New AES-Standard:

Y

Y

In S-video, "Y" is an abbreviation for luma of a color video signal. ("C" is for chroma.)

Y/C

Broadcast NTSC with separate color. Y = luma and C = chroma.

Y/C separator (YCS)

The process of converting composite video to itsluma and chroma components (YC or S-video).

Y, R-Y, B-Y

Color difference signal designation. Y corresponds to the luminance signal; R-Y corresponds to the red minus luminance signal, and B-Y corresponds to the blue minus luminance signal. These signals are derived as follows:

Y = 0.3 red + 0.59 green + .11 blue
R-Y = 0.7 red
0.59 green
0.11 blue
B-Y = 0.89 blue
0.59 green
0.3 red

Y signal

The luma signal transmitted in standard color video. In a color picture, the Y signal is made up of 0.30 red, 0.59 green, and 0.11 blue. It is compatible with a standard monochrome receiver.

Y to C delay

Relative delay or timing of the luminance channel compared to the chrominance channel in a video system.

Y, U, V

PAL luminance and color difference components. U and V are the names of the B-Y and R-Y color difference signals (respectively) when they are modulated onto a subcarrier.

Z

Z: A symbol for impedance.
Zoom: A term used with cameras and video displays related to the ability to change the view anywhere between near and far. Definitions for near and far vary from one device to another.
Zoom lens: A lens with a variable focal length.