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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,