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Your Ultimate Audio Visual Glossary

acoustics – the science of sound wave behavior in the air.

AES – Audio Engineering Society.

alternating current (AC) – an electric current that reverses its direction periodically.

ambient light – all light in a viewing room produced by sources other than the display.

ambient noise – a sound that is extraneous to the intended, desired, intentional, audio; background noise.

amplifier – an electronic device for increasing the strength of electrical signals.

amplitude – the strength of an electronic signal as measured by the height of its waveform.

analog – a method of transmitting information by a continuous but varying signal.

angularly reflective screen – a screen that reflects light back to the viewer at a complementary angle.

ANSI – American National Standards Institute.

aperture – an opening in a lens regulating the amount of light passing through the lens to the imager.

artifacts – small disturbances that affect the quality of a signal.

aspect ratio – the ratio of image width to image height (typically widescreen or standard).

attenuate – to reduce the amplitude (strength) of a signal or current.

audio processor – an electronic device used to manipulate audio signals in some manner.

audio signal – an electrical representation of sound.

audio transduction – converting acoustical energy into electrical energy, or electrical energy back into acoustical energy.


balanced circuit – a circuit in which two branches are electrically alike and symmetrical with respect to a common reference point, usually ground; preferred to an unbalanced circuit due to its ability to reject noise.

bands – a grouping or range of frequencies.

bandwidth – a measure of information-carrying capacity without distortion.

bandwidth limiting – the result of encoding a higher quality signal into a lower-quality form, such as RGB converted into S-Video.

baseband – video signal that has not been modulated.

bend radius – the maximum amount a conductor can be bent before excessive attenuation is encountered, signal integrity is compromised, or the conductor breaks.

bi-directional polar pattern – the shape of the region where some microphones will be most sensitive to sound from the front and rear while rejecting sound from the top, bottom, and sides.

bit – shortened form of binary digit, symbolized by 1s and 0s. The smallest unit of digital information.

bit depth – the number of bits used to describe data.

blocking – pieces of wood that have been inserted between structural building elements to provide a secure mounting point for finish materials or products.

block diagram – an illustration of the signal path through a given system.

BNC – a professional type of video connector featuring a two-pin lock.

boundary microphone – a microphone that relies on reflected sound from a surrounding surface.

buffer amplifier – an electronic device that provides some isolation between other components.

bus (buss) – a wiring system that delivers power and data to various devices.

byte – an 8-bit word is called a byte. The acronym for byte is the upper-case B.


cable – an assembly of more than one conductor (wire).

capacitance – the ability of nonconductive material to develop an electrical charge which can distort an electrical signal.

capacitive reactance – the opposition a capacitor offers to alternating current flow. Capacitive reactance decreases with increasing frequency or, for a given frequency; the capacitive reactance decreases with increasing capacitance. The symbol for capacitive reactance is XC.

captive screw connector – sometimes called a Phoenix(R) connector, it is a molded plastic connector whose termination requires that you strip and slide a wire directly into a slot on the connector. A set screw then pushes a gate down to hold the wire in place.

cardioid – heart-shaped region where some microphones will be most sensitive to sound predominately from the front of the microphone diaphragm and reject sound coming from the sides and rear.

carrier – modulated frequency that carries video or audio signal.

category 5 (Cat 5) – the designation for 100-ohm unshielded twisted-pair cables and associated connecting hardware whose characteristics are specified for data transmission up to 100 Mb/s. (Part of the EIA/TIA 568A standard.)

category 5e (Cat 5e) – enhanced version of the Cat-5 cable standard that adds specifications for far end crosstalk. (Part of the EIA/TIA 568A standard.)

category 6 (Cat 6) – cable standard for Gigabit Ethernet and other interconnect that is backward compatible with Category 5 cable, Cat-5e and Cat-3. Cat-6 features more stringent specifications for crosstalk and system noise. (Part of the EIA/TIA 568A standard.)

CATV – Community Antenna Television system. Broadcast signals are received by a centrally located antenna and distributed by cable through a region.

CCTV – (See closed circuit television).

charged-coupled device (CCD) – a semiconductor image-sensing device, commonly used in video and digital cameras, that converts optical images into electronic signals.

chrominance – the color portion of a composite or S-Video signal.

clock adjustment – also called timing signals, used to fine-tune the computer image. This function adjusts the clock frequencies that eliminate the vertical banding (lines) in the image.

closed circuit television (CCTV) – a system of transmitting video signals from the point of origin to single or multiple points equipped to receive signals.

coaxial cable – a cable consisting of a center conductor surrounded by insulating material, concentric outer conductor, and optional protective covering, all of the circular cross-section. Abbreviated coax.

CODEC – an acronym for coder/decoder. An electronic device that converts analog signals, such as video and audio signals, into digital form and compresses them to conserve bandwidth on a transmission path.

color burst – that part of an NTSC video signal that carries the color information. It is a signal consisting of several (8 to 10 in NTSC) cycles of unmodulated color subcarriers, superimposed at a specified location within the composite signal.

color difference signals – signals which convey color information such as hue and saturation in a composite format. Two such signals are needed. These color difference signals are R-Y and B-Y, sometimes referred to as Pr and Pb or Cr and Cb.

comb filter – transversal filter that combs out a specific set of frequencies. Comb filters are very effective in separating the chrominance and luminance sidebands in an NTSC video signal.

combiner – in a process called multiplexing, the combiner puts signals together onto one cable constituting a broadband signal.

common-mode – refers to either noise or surge voltage disturbances occurring between the power neutral (white wire) and the grounding conductor (green wire). Unwanted common-mode disturbances exist as a result of noise injection into the neutral or grounding wires, wiring faults, or overloaded power circuits.

common-mode rejection ratio (CMRR) – The ratio of the common-mode interference voltage at the input of a circuit, to the corresponding interference voltage at the output.

component video – color video in which the brightness (luminance) and color hue and saturation (chrominance) are handled independently. The red, green, and blue or, more commonly, the Y, R-Y, B-Y signals are encoded onto three wires. Because these signals are independent, processing such as chroma keying is facilitated.

composite video signal – the electrical signal that represents complete color picture information and all synchronization signals, including blanking and the deflection synchronization signals to which the color synchronization signal is added in the appropriate time relationship.

compression – the action of the air molecules moving closer together permitting audible sound.

compressor – a compressor controls the overall amplitude of a signal by reducing that part of the signal which exceeds an adjustable level (threshold) set by the user. When the signal exceeds the threshold level, the overall amplitude is reduced by a ratio, also usually adjustable by the user.

condenser microphones – also called a capacitor microphone, it transduces sound into electricity using electrostatic principles.

conductor – in electronics, a material that easily conducts an electric current because some electrons in the material are free to move.

cone – most commonly used component in a loudspeaker system and found in all ranges of drivers.

conferencing systems – the technology by which people separated by distance come together to share information. Conferencing systems may include projection, monitor displays, computers, satellite connections video and audio playback devices, and much more.

continuity – the quality of being continuous (as in a continuous electrical circuit).

control track – the portion along a length of a recorded tape on which sync control information is placed; used to control the recording and playback of the signal.

CPU – (central processing unit); the portion of a computer system that reads and executes commands.

crosstalk – any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.

CRT – Cathode Ray Tube; the video display tube used in monitors and receivers, radar displays, and video computer displays. The CRT is a high-vacuum tube containing an electron gun to produce the images seen on the face of the tube.

current – the amount of electrical energy that is flowing in a circuit.

curvature of field – a blurry appearance around the edge of an otherwise in-focus object (or the reverse) when the velocity of light going through the lens is different at the edges than at the center of the surface, due to the lens design.


D-sub connector – a generic name for D-shaped serial connectors used in data communications.

DA – (see distribution amplifier)

decibel – a comparison of two measurements or values. Abbreviated dB, it is one-tenth of a Bel (a unit of measurement named for Alexander Graham Bell).

deflection coil – a uniform winding of wire used to electromagnetically direct an electron beam to draw an image on a cathode ray tube (CRT).

delay – an audio signal processing device or circuit used to retard the speed of transmission on one or more audio signals or frequencies.

demodulator – electronic device that removes information from a modulated signal.

depth-of-field – the area in front of a camera lens that is in focus from the closest item to the camera to the furthest away.

differential-mode – refers to either noise or surge voltage disturbances occurring between the power hot and the neutral conductor. Most differential mode disturbances result from load switching within a building, with motor type loads being the biggest contributor.

diffusion – the scattering or random redistribution of a sound wave from a surface. It occurs when surfaces are at least as long as the sound wavelengths, but not more than four times as long.

digital – a method of transmitting information by discrete, non-continuous impulses.

digital-to-analog converter – an electronic device that converts digital signals into analog form.

D-ILA – Digital Direct Drive Image Light Amplification projectors.

DIN connector – Deutsche Industrie-Norm (DIN) – a connector that follows the German standard for electronic connections.

direct current (DC) – electricity that maintains a steady flow and does not reverse direction, unlike alternating current (AC). Usually provided by batteries, AC to DC transformers, and power supplies.

direct sound – also known as near-field, it is sound that is not colored by room reflections.

dispersion – can be seen when a white light beam passes through a triangular prism. The different wavelengths of light refract at different angles, dispersing the light into its individual components.

distributed sound – a sound system in multiple loudspeakers separated by distance and typically operates in a lower sound pressure level than a high-pressure system. The loudspeakers are most often suspended over the heads of the listeners.

distribution amplifier – an active device used to split one input into multiple outputs while keeping each output isolated, and the signal level constant.

DLP – Digital Light Processing(c) by Texas Instruments. A projection system that has technology based on the Digital Micromirror Device (DMD). It uses thousands of microscopic mirrors on a chip focused through an optical system to display images on the screen.

document camera – an imaging device used to create a video image of printed documents or three-dimensional objects.

dome – used in all ranges of drivers.

driver – in audio, an individual speaker unit.

DTV – Digital Television; a signal transmitted digitally.

DVD – Digital Video Disc or Digital Versatile Disc; an optical storage medium for data or video.

DVI – Digital Visual Interface; a connection method from a source (typically a computer) and a display device that can allow for direct digital transfer of data. The digital signal is limited to 5 meters.

DVI-D – one of two common multi-pin connectors available for DVI signals. The DVI-D carries no analog video information, only digital. The digital signal is limited to 5 meters.

DVI-I – one of two common multi-pin connectors available for DVI signals. The DVI-I adds analog video to the connection, permitting greater distances than the digital limit of 5 meters.

dynamic microphone – a pressure-sensitive microphone of moving coil design that transduces sound into electricity using electromagnetic principles.

E— 

early reflected sound – created by sound waves which are reflected (bounced) off surfaces between the source and the listener. The sound waves arrive at the listener’s ear closely on the heels of the direct sound wave.

echo cancellation – a means of eliminating echo from an audio path.

EIA – Electronics Industries Alliance. The association which determines recommended audio and video standards in the United States.

electromagnetic interference (EMI) – an electrical disturbance caused by an electromagnetic field, either low frequency or RF

EMI – (See electromagnetic interference.)

emissive technology – any display device that emits light to create an image.

encoded – a signal that has been compressed into another form to reduce size or complexity, as in a composite video signal.

equalizer – electronic equipment that adjusts or corrects the frequency characteristics of a signal.

equipment rack – a centralized housing unit that protects and organizes electronic equipment.

Ethernet – a set of network cabling and network access protocol standards for bus topology computer networks invented by Xerox but now controlled by the 802.3 subcommittee of the IEEE.

expander – an audio processor that comes in two types: a downward expander and a part of a compander.


F connector – a threaded connector that is used in transmission applications such as cable television. The cable’s center conductor also serves as the connector’s center pin.

feedback – 1. unwanted noise caused by the loop of an audio system’s output back to its input. 2. in a control system, data supplied to give an indication of status, i.e., on or off.

fiber optic – a technology that uses glass or plastic threads or wires to transmit information.

field – one half of a video frame containing every other line of information. Each standard video frame contains two interlaced fields.

filter – filters remove or pass certain frequencies from a signal.

fixed matrix – a type of display that has a fixed grid on which it recreates an image.

flex life – the number of times a cable can be bent before it breaks. A wire with more strands, or more twists per inch, will have a greater flex life than one with a lower number of strands, or one with less twists per inch.

focal length – abbreviated as FL, it is the distance, in millimeters, between the center of a lens and the point where the image comes into focus. The value given to a lens, stated in inches or millimeters. The shorter the focal length, the wider the angle of the image.

focus – the act of adjusting a lens to make the image appear clear, sharp, and well-defined.

footcandle – abbreviated as Ftc, it is an English unit of measure expressing the intensity of light illuminating an object. The illumination from one candle falling on a surface of 1 square foot at a distance of 1 foot.

footprint – 1. indicates where possible mounting points are to join two pieces together, the total contact area, and how they may or may not fit together. 2. space required to house an equipment rack or device. 3. coverage area of a communications satellite.

frame – 1. an individual segment of film 2. a complete video picture or image of odd and even fields; two fields equal one frame.

frequency – cycles per second, expressed in Hertz (Hz) or the number of cycles in a given time period.

frequency response – the range of frequencies within which a microphone is sensitive.

fresnel lens – a flat glass or acrylic lens in which the curvature of a normal lens surface has been collapsed in such a way that concentric circles are impressed on the lens surface; often used for the condenser lens in overhead projectors, in rear projection screens, and in-studio spotlights.

front screen projection – a system that employs a light-reflecting screen for use when the image will be projected from a source in front of the screen.

f-stop – the ratio of focal length to the effective diameter of a lens; also called f-number, it represents how much light is able to pass through the lens.

fundamental frequency – the lowest frequency in a harmonic series; known as “pure tone.”


gain – 1. electronic signal amplification. 2. the ability of a projection screen to concentrate light.

gate – an audio processor that allows signals to pass only above a certain setting or threshold.

gauge – a thickness or diameter of a wire.

genlock – to lock the synchronization signals of multiple devices to a single source; the condition which exists when the sync generators of multiple devices are locked to a single source.

glass bead screen – screen covered with tiny glass beads, each of which provides a spherically reflective surface.

graphics adaptors – commonly referred to as a “video card”, which outputs computer signals.

grounding – the techniques and hardware that connect electronic equipment and wiring to a reference point.


harmonics – higher frequency sound waves that blend with the fundamental frequency.

HDTV – High Definition Television.

headend – the equipment located at the start of a cable distribution system where the signals are processed and combined prior to distribution.