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Glossary

 

Glossary of Audio and Video Terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

acoustic feedback - In LP-record playing, an undesirable sound that is caused by vibrations from the loudspeaker creating extra vibrations in the cartridge stylus.

acoustic suspension - A type of loudspeaker in which the motion of the woofer cone is stabilized by air pressure within the sealed cabinet.

AM (amplitude modulation) - A method of broadcasting in which the desired audio or video signal modulates the amplitude of a 'carrier' signal.

analog - information that is reproduced using a continuously varying electronic signal. h video terms, its opposite is digital.

antenna - An array of metal rods or wires used to intercept radio waves and convert them into electrical currents.

aspect ratio - The proportions of a TV or film picture, generally given as the ratio of the width to height. The standard TV picture has an aspect ratio of 4x3, or 4:3. High-definition video systems may have aspect ratios of 6x8 or greater.

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B

bandwidth - (1) The range of frequencies over which a device operates effectively. (2) The range of frequencies required for transmitting different types of electronic signals. Color TV needs a broad band-about 4.6 MHz; the telephone requires only a narrow band, less than 4 kHz.

bass - The lowest audible frequencies, between approximately 20 and 200 cycles per second.

bass reflex - A type of loudspeaker whose low-frequency response is augmented by sound waves emerging from within the cabinet via a port or freely suspended cone. Also called a 'ported ' or 'vented ' speaker.

Beta - The first successful home videocassette system, using 1/2-inch (1.27 cm) tape.

bias - In tape recording, an ultrasonic signal that is mixed with the audio signal during recording. Bias reduces noise and distortion and affects the frequency response.

binaural - Stereo recordings that are made with microphones mounted in a dummy head and intended for playback through headphones.

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C

cable TV - Method of non-broadcast distribution of video programs directly to homes, generally employing coaxial or fiber-optic cable.

camcorder - One-piece combination video camera and recorder.

carrier wave - An electronic signal that is capable of carrying information when the signal is modulated.

cartridge (cartridge, stereo) - The phonograph pickup, consisting of a stylus assembly and the miniature circuits that transform stylus vibration into an electrical signal.

CATV - Community antenna television. - the predecessor of cable TV. The initials now often refer to cable TV.

C-band - The portion of the microwave spectrum (4,000-8,000 MHz) used most widely for distribution of video programs by satellite to cable systems.

CCD (charge-coupled device) - A semiconductor chip used as a highly efficient light sensor in video cameras.

CCTV - Closed-circuit television.

CD (compact disc) - A digitally encoded record, aluminized to reflect light and played with a low-power laser. A 12-cm (4.7 - in) CD contains up to 74 minutes of stereo sound.

CD-I (compact disc-interactive) - A "multimedia" .CD combining audio, video, still pictures, and text and used in conjunction with TV.

CD-ROM - Compact Disc-Read Only Memory; a laser-read, computer-accessible disc that stores large quantities of digitized data.

CD-V (compact disc-video) - A variant form of CD containing up to 6 minutes of video and 20 minutes of digital audio.

coaxial - Refers to devices having the same center. In a coaxial speaker, the tweeter is mounted in the center of the woofer. A coaxial cable consists of a central wire surrounded by insulation and an outer wire forming a cylindrical shield against interference.

COMSAT - Communication Satellite Corporation, providing satellite communication services and chartered by the federal government.

crossover - An electronic filter circuit that separates low from high frequencies and channels them to the woofer and tweeter, respectively.

CRT (cathode ray tube) - The screen usually used on a TV set or on a computer terminal.

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D

DAT - Digital audio tape, usually packaged in a cassette. DAT employs the same digital coding and provides the same sound quality as the compact disc.

database - Computerized store of information that can be reached only via a computer.

DBS - Direct Broadcast Satellite; a system that sends TV broadcasts directly from a communications satellite to home antennas, or dishes.

DBX - An audio equipment manufacturer and developer of noise-reduction systems used in tape recording and in stereo television sound.

DCC (Digital Compact Cassette) - A cassette tape format that employs perceptual coding.

digital - (1) A method of representing sound waves as a series of binary numbers. (2) A tuning method for radios in which the desired freq. is set by digital alculation. (3) A numeric display of information.

Digital signal processing (DSP) - Describes various digital processes to enhance analog transmission.

digital television - TV transmission in the form of binary data making possible more precise processing of the picture.

direct drive - A turntable drive system in which the spindle and platter are part of the motor itself.

dish - The parabolic antenna used for transmitting and receiving signals from communication satellites.

distortion - Changes in a signal that involve the addition of spurious tones at frequencies not present in the original sound. In harmonic 'distortion' the spurious tones are at integral multiples of the original frequency. In 'intermodulation' distortion, discordant tones appear at the sums and differences of two original frequencies.

Dolby B, C, and S - :Noise-reduction circuits for consumer tape recorders. Two other circuits, Dolby A and SR, are used in recording studios.

Dolby Digital - A system of five-channel surround sound for motion pictures, based on Dolby AC-3 perceptual coding.

Dolby Stereo - A system of noise-reduction, equalization, and surround sound, used for motion-picture sound tracks.

DOMSAT - Domestic communication satellite (as opposed to one confined to military uses).

dropout - A momentary loss of signal in a tape recording, usually caused by wear, dust. or a tape defect.

dubbing - ( 1) The process of copying a recording to make a duplicate. (2) In motion-picture sound, replacing a foreign language soundtrack with dialogue in the language of the audience.

dynamic range - The ratio between the loudest and softest sounds that can be reproduced accurately by a recording medium.

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E

Earth station - The ground station that receives (downlink) and sends (uplink) signals to and from communication satellites.

edit, electronic edit - The removal, or the joining together, of sections of film or video tape material. In film editing, the material is actually cut out, or pasted together mechanically. In electronic editing of videotapes, video tape recorders make the required changes electronically.

electronic image stabilizer(EIS) - A digital feature in some camcorders that compensates for unintended camera movement.

ENG - Electronic news gathering; the use of video cameras and tape recorders in place of film systems for news coverage by TV stations.

equalization - Changes in amplification at low or high frequencies, done to compensate for the limitations of a recording medium and to obtain equally accurate reproduction at all frequencies.

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F

FAX (facsimile transmission) - A system that transmits pictures or prints electronically.

field - A set of scanning lines that, when interlaced with another set, makes up the 'frame,' or complete TV picture.

flutter - Unwanted variation in the speed of a turntable or tape recorder. Slow flutter, or 'wow,' causes musical sound to waver in pitch.

FM (frequency modulation) - A method of broadcasting or recording in which the desired audio or video signal modulates (varies) the frequency of a "carrier" signal.

FMX (Extended-range FM.) - A noise-reduction system that claimed hiss-free reception of FM broadcasts at larger distances or with smaller antennas.

footprint - The particular patch of the Earth's surface reached by the signal from a communications satellite.

frame - A complete TV picture, comprising two fields. The U.S. transmission standard calls for 30 frames transmitted per second.

frequency . The number of cycles per second of an electromagnetic transmission. 1 hertz (Hz) = 1 cycle per second; 1 kilohertz (kHz) = 1,000; 1 megahertz (MHz) = 1,000,000; 1 gigahertz (GHz) 1 billion.

frequency response - The principal measures of the fidelity of any sound reproducing device.

front projection - A type of projection TV system in which the picture is projected onto a reflective screen, which is viewed from the same side as the source of the projected picture.

fuzzy logic - A form of artificial intelligence, stored on a computer chip, that enables a camcorder or television to make complex adjustments in focus or picture quality based on ideal models.

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G

geostationary orbit - The orbit of a communications satellite that allows it to move at the precise speed at which the Earth is rotating, thus remaining at the same spot in the sky relative to the Earth. The orbit is 35,900 km (22,300 mi) above the Earth and directly over the equator.

graphic equalizer - A tone-control device whose amplification can be varied by octave, using slider controls whose positions provide an approximate visual graph of the frequency response.

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H

HDTV - High-definition TV, a technology aimed at producing a video picture containing as much detail as a 35-mm motion picture, with a wide-screen aspect ratio and stereophonic sound.

head - in video and audio, an electromagnetic device that both lays down the magnetic track on recording tape and reads an existing track.

helical scan - The basis for most modem videotape recording, in which the signal is recorded as a diagonal track by recording heads on a rapidly revolving drum. The same heads, revolving at the same speed, are used for playback.

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I

impedance - Opposition or resistance to the flow of electrical current. The rated impedance of a loudspeaker is an average, since the impedance depends on the frequency of the signal.

integrated amplifier - An amplifier containing the pre-amplifier and the power supply in one unit.

INTELSAT - International Telecommunications Satellite Organization; 112-member consortium of countries formed (1964) to launch and operate communications satellites.

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J

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K

kinescope - A TV picture tube. Also, a photographic film made from a TV transmission as it appears on the tube. Once used for recording TV programs, it has been replaced by videotape recording.

Ku-band - The portion of the microwave spectrum (12,000-18,000 MHz) used in many newer video satellite transmissions, particularly in Direct Broadcast Satellite (DBS) systems designed for home reception.

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L

LaserVision, Laser Disc - Trade names for the optical video disc system in which picture and sound are recorded, and read out by laser.

LCD (liquid crystal display) - A thin, flat glass 'sandwich' enclosing a layer of voltage-sensitive liquid. Widely used for calculator and watch displays and, more recently, for portable computer readouts and 'pocket television" screens.

LED (light-emitting diode) - Solid-state devices that glow when electric current is applied.

loudness compensation - A tone-control process that boosts low frequencies at low volume levels, in an attempt to compensate for the ear's insensitivity to quiet bass sounds.

LPTV - Low-power TV; TV station with limited broadcasting range, often built in rural areas in order to pick up and amplify distant signals. Also used for broadcast programming to specific audiences.

lux - Unit of light illuminance. Used as a measure of low-light recording capacity in video cameras.

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M

MATV - Master antenna television; a distribution system in which a single antenna is used to feed broadcast TV signals to the occupants of a building or development. SMATV provides the same service but uses a dish antenna to pick up satellite transmissions.

MD (MiniDisc) - A miniature digital audio disc, based on perceptual coding. A play-only MD is a miniature CD. A recordable MD is a magneto-optical disc.

MDS - Multipoint distribution service; a method of distributing video programs from a central high point (usually a tall building) by microwave to subscribers equipped with special antennas. Sometimes called 'wireless cable.'

midrange - Frequencies in the range spanned by the human voice, from approximately 200 to 2,000 cycles per second.

modem - A device used for accessing computer data over telephone lines.

monitor - A video display used in TV studios and designed to receive direct input of video signals from studio cameras, videotapes, and other signal producing equipment.

monitor-receiver - A television receiver that has video inputs enabling it also to serve as a monitor

monophonic, monaural - Recording or playback involving only one channel of sound.

MTS - Multichannel TV sound; provides additional sound channels along with a single picture on a TV channel. The U.S, transmission system can include stereophonic sound as well as additional sound channels.

multipath - Reception of one or more reflected signals along with a direct broadcast signal, producing distortion in stereo FM and ghost images in televisions

multiplex - A method of accommodating two channels of information on one carrier, for example, two channels of sound in one FM broadcast.

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N

narrowcasting . Transmission to a specific, small audience (such as Japanese speaking people for example), often via low-power, UHF stations.

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O

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P

PAL - Phase Alternation Line color system, the color TV broadcast standard used in most of Western Europe and. in modified form, in China and Brazil.

pay cable - scrambled TV pictures of premium programs, transmitted by cable, designed for viewing only by those paying a monthly fee for home decoders.

pay-per-view, PPV - A form of pay TV where a specified fee is paid for watching each program selected.

perceptual coding - An approach to digital coding that records only the portions of sound or picture: that we believed to be audible or visible.

phase - The relative timing of two signals. If signals are 'in phase,' they are precisely synchronized. If loudspeakers are wired 'out of phase', one is 'pushing ' when the other is 'pulling'.

picture in picture, PIP - A television feature in which a small screen can be displayed within the large screen, allowing the viewer to watch (though not hear) two channels simultaneously. The second picture must usually be sourced through a VCR, although there are televisions with two tuners.

pixel - Picture element; the smallest area of a video picture capable of being delineated by an electrical signal. The number of pixels in a complete picture determines the amount of detail or resolution in the picture. In the United States the TV picture generally holds a maximum of 150,000 pixels.

power amplifier - The portion of an amplifier that produces the high current levels needed to drive a loudspeaker.

preamplifier - The portion of an amplifier that amplifies low level signals and includes most operating controls.

projection television - A television or video display system in which the picture is projected onto a screen, generally from three separate cathode ray tubes, one for each primary color.

pulse code modulation - one method of digitizing an analog picture.

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Q

quadraphonic - Surround-sound reproduction involving the recording and playback of four channels of sound.

quantization - The representation of a continuous quantity, such as a sound wave, by a series of numeric values.

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R

rear projection - A projections TV system wherein the picture is projected onto a translucent screen , which is view from the opposite side.

receiver - Generally speaking, any device that receives broadcasts. In Hi-Fi equipment, an integrated amplifier and radio tuner combined in the same chassis.

resolution - Standard measurement of the amount of detail that can be seen in a TV-screen image, expressed in the number of horizontal lines on a test pattern.

resonance - The natural tendency of a device to vibrate at a specific frequency. Unwanted resonances in loudspeakers, for example, alter the sound by producing excessive response at some frequencies.

RF - Radio frequency, the electromagnetic wave 'carrier' that conveys the modulated video signal from a TV station to a home receiver.

rumble - Low-frequency noise caused by vibration of the motor and bearings of a turntable.

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S

S/N ratio (signal-to-noise ratio) - The range, usually expressed in decibels, between the loudest sound a recording medium can accommodate and its background noise level.

sampling - Part of the process of digital recording dissection of a signal in time, preparatory to quantization.

SATCOM - RCA's communication satellites.

scrambling - A method of altering a cable or satellite transmission signal so that it can be seen only by those who own special decoders.

SECAM - Sequentiel Couleur avec Memoire (sequential color with memory); the color TV broadcast standard used in France and its former possessions and, in modified form, in the USSR and some Eastern European countries.

selectivity - A measure of a tuner's ability to receive stations at closely spaced frequencies without mutual interference.

signal - A sound wave, transmitted as an electrical waveform or its digital representation.

stereophonic - Sound reproduction that uses two or more channels in order to represent the size or spatial distribution of sound sources

STV - Subscription TV; broadcast TV, transmitted in scrambled form, for which a decoder is needed.

surround - Sound reproduction that surrounds the listener with sound, as in quadraphonic recording and reproduction.

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T

THD (total harmonic distortion) - A measure of all of the spurious signals added by a sound-reproducing device.

tone control - A method of altering the timbre of reproduced sound by increasing or decreasing the amplification at either high or low frequencies.

track - The area on a tape where a signal 'is recorded.

tracking force - The downward force applied to a stylus to maintain uniform contact with the undulating groove wall.

transducer - A device that changes a signal to a different physical form while maintaining its pattern: as in the phonograph cartridge , which transforms stylus motions into electrical signals, or the loudspeaker, which transforms electrical signals into sound waves.

transponder - Device on a communications satellite that receives electromagnetic signals and transmits them back to Earth.

transport - The portion of a tape recorder that moves the tape past the heads at constant speed.

treble - The highest audible frequencies, between approximately 2,000 and 20,000 cycles per second.

TVRO - TV receive - only Earth station; such as a home dish antenna.

tweeter - A small loudspeaker that reproduces high frequencies.

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U

UHF - Ultra high frequencies; used by TV channels 14 to 82.

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V

VCR - Videocassette recorder, in which the tape is enclosed in a cassette and the loading within the machine is automatic.

VDT - Video display terminal; generally used with a computer.

vertical blanking interval (VBI) - The 21 lines between TV frames, transmitted, like the frames, at a rate of 30 times per second. The se lines are used for auxiliary information, including teletext, closed captions, and test signals.

VHD - Video High Density (or Video Home Disc); a grooveless record whose video signals are read by a floating stylus.

VHF - Very high frequencies, used by TV channels 2 to 13.

VHS - A videocassette format. using 1/2-inch (1.27-cm) tape. VHS-C is a smaller VHS cassette. Super-VHS (S-VHS) incorporates advanced digital circuitry.

videodisc - A disc resembling a phonograph record that stores both picture and sound for playback.

videotex -Interactive (two-way) system for accessing written and graphic information on video screens and computer display terminals, which are linked to central computers via telephone lines.

VTR - Videotape recorder, using either cassettes or open reels.

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W

watt - A unit of electrical or acoustical power. Electrical power is the product of voltage and current. Acoustical power is proportional to sound-pressure intensity.

woofer - A large loudspeaker that reproduces low frequencies.

wow - Slight variations in the speed of a tape or record player, causing the musical pitch to wobble.

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X

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Y

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Z

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This article was published on Tuesday 14 December, 2004.
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