Resource Center: How to Speak A/V
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Entries starting with: CableCARD: A removable electronic card supplied by a cable-TV service provider that enables reception of encrypted premium channels without a separate decoding box when it’s inserted in a digital cable-ready HDTV. cable modem: A broadband Internet hookup where the modem connects through a cable-TV line rather than a phone line. camcorder: A portable, handheld combination video camera and video recorder. capture ratio: A measure, in decibels, of an FM tuner’s ability to reject all but the strongest signal on a tuned frequency; lower figures are better. cardioid microphone: A microphone whose highest sensitivity is directly perpendicular to its diaphragm, usually straight ahead, and that rejects sounds from the sides and rear (compare omnidirectional microphone, shotgun microphone); the most common type of microphone in a camcorder. carrier: A high-frequency sine wave whose alterations in amplitude, frequency, or phase are used to convey (carry) the information in a much lower-frequency signal or band of signals; used, for example, in AM and FM radio broadcasting. Category 5 (Cat-5): Network cabling consisting of four twisted pairs of copper wire terminated by eight-conductor RJ-45 connectors; supports data rates up to 100 megabits per second. Category 6 (Cat-6): Like Cat-5, but supports data rates up to 1 gigabit per second (Gigabit Ethernet). CD (compact disc): A polycarbonate disc 12 centimeters (approximately 4[3/4] inches) in diameter that can store more than 80 minutes of stereo sound in 16-bit linear PCM digital format. A laser pickup reads reflections from the microscopic “pits” and “lands” on its internal metallized information layer. CD-R (compact disc–recordable): A format that permits data to be written onto a special type of blank CD but not erased from it. CD-RW (compact disc–rewritable): A format that permits data to be written onto and erased from a special type of CD. CD Text: Artist names, track titles, and the disc title stored as text on some CDs; you need a CD Text-capable CD player to read and display this information. center channel: A third front channel used to complement the front left and right stereo channels in a multichannel audio/video or surround sound system; its primary purpose is to stabilize the center of the reproduced soundstage for off-center listeners — which enables it to be the main channel for dialogue in movie soundtracks. channel: In audio, a distinct path for a signal; stereo signals have two channels; multichannel systems such as Dolby Digital, DTS, and Dolby Surround (Pro Logic) use additional channels for a center speaker in front and surround speakers at the sides or rear. In Dolby Digital and DTS, an LFE channel is devoted to loud low-frequency sound effects. In broadcasting, a channel is a specified frequency band assigned to carry a station’s signal. channel separation: A measure of the amount of signal leakage between audio channels, expressed in decibels; higher figures are better. charge-coupled device (CCD): A semiconductor technology used to make, among other things, the solid-state image sensors used in camcorders. chip: An integrated circuit, so called because it usually is a small piece of silicon chipped off a larger “wafer” that may contain hundreds of other circuits. In a video camera the term applies to the image-sensing charge-coupled device, of which there can be as many as three. chrominance (C): A video signal carrying only the point-to-point color, both hue and saturation, of a video image and not its brightness; see luminance. Class A: An amplifier operating design in which the output devices conduct current at all times — an inefficient technique that eliminates crossover distortion. Class AB: A very common amplifier configuration that is designed to minimize crossover distortion at low signal levels while maintaining higher operating efficiency than a Class A design. Class B: A more efficient type of amplifier configuration than Class A or AB in which no current flows through an output device when it is not carrying a signal. While prone to crossover distortion, Class B designs have been successfully used as amplifiers in powered subwoofers. Class D: So-called digital amplifiers, not because they’re driven directly by binary data but because the output circuits are always either fully on or off. Operation is similar to that of a switch-mode power supply, except that audio signals control the switching action. Efficiency is very high, making Class D amps desirable for compact and battery-powered portable gear. client: A component that receives information (such as digital music, movies, or photos) through a wired or wireless network; see media server. clipping: Overload distortion that occurs when an electronic device such as the amplifier in a stereo or home theater system cannot accommodate the maximum level requirements of the input signal, shearing off (“clipping”) the waveform peaks of the music or movie soundtrack. clone: A digital copy that is a perfect (bit-accurate) numerical reproduction of an original digital signal. closed captioning: A system that transmits caption or subtitle text and symbol data in the nonimage portion of a video signal. It requires special decoder circuitry for display, hence the “closed.” coaxial: A type of cable construction in which an inner conducting wire is surrounded by a shielding cylindrical outer conductor; commonly used in video and digital audio connections. Connectors maintaining this construction may also be referred to as coaxial. Also refers to a speaker configuration in which two drivers are mounted one behind the other so that their centers are in line. coloration: A frequency-response anomaly that alters the perceived timbre of sound, making a voice sound unnatural, for example. color balance: see white balance. color control: A TV adjustment that changes the amount of chrominance applied to the image; also see saturation. color difference: A system of transmitting video information — as on DVDs and in component-video signals — in which the color signals contain the difference between a given primary color (red, blue, or green) and the luminance signal. color temperature: The specific shade of white produced by a TV in response to a pure-white (luminance-only) input signal, measured in kelvins (K). Low color temperatures produce a “white” that’s tinted reddish-orange compared with the bluish “white” at high color temperatures. comb filter: In video equipment, a circuit that separates the chrominance from the luminance signals contained in a composite-video signal. Music producers use comb filters in the recording studio to generate “phasing” and “flanging” effects. CompactFlash card: A small, removable data-storage format, generally flash memory but also encompassing ultra-miniature hard-disk drives; used in many digital still cameras and a few portable MP3 players. component: A separate piece of audio or video equipment, with its own chassis and power supply, that performs one specific function or set of related functions. component video: A method of transmitting video signals that continuously keeps the various color components separate from each other. Consumer component-video connections carry luminance and two color-difference signals; see YCrCb and YPrPb. composite video: A single video signal that combines three video subsignals (luminance, chrominance, and sync). Until the development of S-video and component-video outputs, all video connections in consumer products were composite video. compression: A reduction of an audio signal’s dynamic range or of the size of digital audio or video data files. Not all compression is bad: dynamics can be uncomfortably wide (soft sounds get lost in room noise, while loud sounds are deafening), and digital files can be much bigger than they need to be to convey high-fidelity audio and video. continuous average power: The maximum undistorted power that an audio amplifier can deliver on a sustained basis. This specification is meaningful only when accompanied by the load impedance into which the power is delivered, the frequency range over which the rated power can be delivered, and the maximum distortion at the rated power. contrast: In general, the range between the brightest and darkest parts of an image; on a TV, a control that adjusts the overall gain of the video signal on its way to the display; see contrast ratio. contrast ratio: A measure of the maximum and minimum light levels a TV can produce when fed the signals for maximum white and black, respectively. convergence: Adjustments in a CRT-based projection TV that align the primary-color images produced by the three internal CRTs. In a direct-view color TV, convergence refers to the alignment of the beams generated by the three electron guns. crossover (crossover network): A circuit or component comprising low-pass, high-pass, or bandpass filters that separate lower-frequency (bass) signals from higher-frequency (midrange/treble) ones. A crossover is used in a speaker that has more than one driver. In a two-way speaker, the crossover sends the low frequencies to the woofer and the high frequencies to the tweeter. See active crossover and passive crossover. crossover (switching) distortion: A type of distortion that can occur in an audio amplifier when a signal does not smoothly swing from positive to negative or vice versa as it is passed (switched) from one output device to another. crossover frequency (or point): In a crossover network, the frequency at which audio signals are divided so that they can be routed to the appropriate drivers (low frequencies to a woofer and high frequencies to a tweeter, for example). CRT (cathode-ray tube): A vacuum tube in which electrons emitted by a hot cathode are focused into beams and scanned across a phosphor-coated surface to produce a picture. crystal: see quartz. current: The rate of flow of electrical charges in a circuit, measured in amperes. cutoff frequency: The audio frequency at which a rolloff begins to take effect. It is normally specified as the point at which the output falls by –3 or –6 dB, depending on the rolloff. Abbreviations |
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