Click on a letter or number to jump to listings of terms that correspond. [ 5 | A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y ] Term Definition Demo C-Format See VHS-C C-weighting See Frequency Weighting Capacitance The property of a circuit element that permits it to store charge. The number of electrons (charge) it can hold under a given electrical pressure (voltage) is called its capacitance which is measured in farads, or fractions thereof, e.g. microfarads. Capacitor Two metallic surfaces separated by an insulator creating a device that can store an electric charge. It cannot pass DC and will pass AC signals with an impedance that decreases as frequency increases. This property makes capacitors useful in filter and crossover designs. Capture Ratio A specification describing the ability of an FM radio tuner to lock on to one station when there is another on the same frequency that is only slightly less strong. Cathode The electrically negative terminal of a battery, or the electron source of a vacuum tube. Cathode Ray Tube See CRT. CATV Cable television. CAV Constant Angular Velocity. A method of recording a disc (e.g. laserdisc) in which the rotational rate is kept constant from beginning to end. Each rotation can be contrived to hold the same amount of information, such as a single frame of a picture, making perfect 'pause' functions possible in an analog medium. It is wasteful of space, however, as the density of recorded data reduces with increasing distance from the center of the disc. See: CLV. Caveat Emptor From the Latin: let the buyer beware. It is a principle in commerce that, without a warranty, the buyer takes the risk CD CD = Compact Disc. An optical disc format for storing digital signals, developed jointly by Sony and Philips. CD-DA CD-DA = Compact Disc Digital Audio, the original PCM digital music storage format, defined by the Red Book standard. CD-R A disc in the CD format that can be recorded once. Defined by the Orange Book standard. CD-ROM A Read-Only Memory (ROM) in the CD format, used for storing computer data. Defined by the Yellow Book standard. CD-RW A disc in the CD format that can be recorded many times. It is rewritable. CEA-2006 An amplifier rating standard provided by the Cnsumer Electronics Association and adopted my many reputable makers of car-audio amplifiers. CEA-2006 attempts to provide a basis for rating amplifers using RMS output power and a specific load impedance to ensure a useful rating. Center channel A channel driving a loudspeaker located midway between the front left and right loudspeakers. It does most of the work in movie and television audio, anchoring dialogue to the screen. In multichannel music, the featured artist can have a private channel. Must sound as good as, and as similar as possible to, the left and right loudspeakers. In automobiles it is especially important to solidly anchor the center portion of the front soundstage for both the driver and the passenger. See Channel. Channel A signal path. Stereo consists of two channels, starting from the signal source, and ending at the loudspeakers. Multichannel audio can have 5, 6 or 7 channels, plus a so-called .1 channel for low bass sound effects. Channel Separation See: Separation. Chassis The metal frame of a vehicle, or the metal base on which an electrical circuit is constructed. Chroma The color information in a video signal consisting of hue and saturation. See: Chrominance, Saturation, Hue Chrominance The color (hue and saturation) of light, independent of luminance (brightness), or that portion of a video signal that carries this information. Designated by the symbol 'C'. See: Luminance. Circuit Breaker A device designed to protect other electronic devices by opening the circuit when the system is drawing too much power. Since it uses relay contacts, it can be reset manually or automatically. See: Fuse. Circumaural Headphones Headphones having cushions that surround the external ear, resting on the sides of the head, not on the ear itself. See: Supraaural Headphones, In-Ear Headphones. Class A An amplifier design in which both positive and negative polarities of an audio waveform pass through devices that are active (conducting current) at all times. All low-level analog amplifiers are of this type. Class A power amplifiers are relatively uncommon because they generate a lot of heat, even when no signal is being reproduced, thus requiring enormous heat sinks and many output devices if large amounts of power are needed. See: Class AB, Class B. Class AB Basically a Class B power amplifier in which the positive and negative output devices never completely shut off, leaving a residual Class A activity at low signal levels and to smooth the transition from one polarity to the other. Less efficient, and therefore hotter, than Class B, but much cooler running than Class A. The most common form of power amplification. See: Class A, Class B. Class B A power amplifier design in which positive and negative polarities of an audio waveform pass through separate output devices that conduct only when needed. It is difficult to eliminate all distortions created when the devices transition from one polarity to the other (crossover distortion), which has relegated this design to low quality audio and other applications of power amplification where efficiency and cost are of greatest importance. Class D An amplifier design in which the positive and negative output voltages are defined by a pulse-width-modulated output section where the transistors are biased to be either on or off and provide the full voltage available from the power supply directly to an output filter. The output filter turns the pulses into an analog waveform suitable for driving loudspeakers. Clipping Distortion that occurs when an amplifier is driven beyond its voltage, current or power limit. Clipping describes the "cutting off" of signal peaks when the amplifier's limit is exceeded by playing the system too loud. Clipped signals have excess high frequencies, putting tweeters at risk, and some amplifiers become unstable when overdriven, and this also can result in damage to the loudspeakers. So, small amplifiers driven too hard can be more dangerous to loudspeakers than large amplifiers driven within their design range. Closed Captions Text captions that can be made visible on demand. Open captions are a permanent part of the video signal. CLV Constant Linear Velocity. A method of recording a disc (e.g. laserdisc) in which the rotational rate is varied from start to finish so as to maintain a constant velocity of the 'groove' being read by the playback laser. This results in a more uniform data density over the surface of the disc, from inside to outside, allowing for longer recordings. See: CAV. Coaxial Cable A transmission line in which a central conductor is located within a cylindrical outer conductor, separated by insulation. Can be designed to have specific characteristic impedances at radio and TV frequencies to minimize losses. Sometimes used in the much less demanding role of interconnect cables at audio frequencies, where they function as simple shielded wires. Coaxial Loudspeakers Loudspeakers in which the tweeter is located on the central axis of the woofer, and the two are combined in a single structural unit. Codec A combination encoder and decoder for any kind of digital signals, audio or video. See: Perceptual Coding, Compression. Coherence In listening, it describes a kind of perceptual realism in sounds. In measurements, it is a measure of the correlation between the phases of two or more signals. Coil Turns of wire used to create inductance for use in an electrical circuit, or to create a magnetic flux when current is passed through it, or to respond to a changing magnetic field. An electrical impedance of a coil increases with frequency. See also Inductance, Inductor, Voice Coil. Color Temperature A measure of the color of light. In video, the underlying basis for a picture. A low temperature would be associated with a reddish picture, while a high temperature would yield one more bluish. NTSC standards require 6500 degrees Kelvin. Coloration In listening evaluations, a perceived characteristic of a sound that was not in the original recording. Coloration modifies the timbre of voices and musical instruments, and is therefore not a good thing. Comb Filter AUDIO: A characteristic of a frequency response curve that appears when a sound is combined with a delayed version of itself. The name comes from the orderly, repeated, bump-dip-bump-dip visual appearance, looking like a comb. Comb filtering that occurs in a simple signal path can be annoying. However, rooms are very complicated comb filters, due to the many reflected sounds, and common experience tells us that this is usually perceived as a benefit e.g. concert halls. VIDEO: a filter that separates a composite video signal into luminance (black and white) and chrominance (color) components. See: Luminance, Chrominance, Frequency Response, Acoustical Interference. Compliance The force required to move an elastically suspended object a certain distance - e.g. the 'stiffness' of a spring. The diaphragm suspensions in loudspeakers have mechanical compliance. The air inside an enclosure has acoustical compliance. Component Video A video signal consisting of three components: red/green/blue (RGB) or a Color Difference method going by one of several names: Y,U,V or Y, Pb, Pr or Y, B-Y, R-Y. The latter is the method of video storage on DVD's and the component connection is the preferred way to communicate video infomation to displays. The green, blue and red cables may be terminated in either RCA or BNC plugs. See: Chrominance, Luminance, RCA, S-Video, BNC. Composite Video A video signal in which the chrominance and luminance signals are combined, along with synchronizing signals. These tend to use cables, looking like yellow audio cables, with RCA connectors. This is the most basic form of video found on virtually all TV's, VCR's, etc. See: Chrominance, Luminance, RCA, S-Video, Component Video. Compression AUDIO: A reduction in the dynamic range of a system. This can be done deliberately, as is common in radio broadcasts, or it can be the result of overdriving something, such as a loudspeaker where, above a certain level, the device does not respond proportionally to increases in signal level (see Power Compression). ACOUSTICS: A momentary increase in pressure as a sound wave passes. See: Rarefaction, Sound Wave. DIGITAL DATA: Reducing the amount of digital data required to store audio or video. Data compression can be lossless or lossy, depending on whether the reconstruction is exact or not. Perceptual coding is used in lossy systems. See: Perceptual Coding. Compression Driver A loudspeaker driver especially designed to drive a horn. The name derives from the fact that the sound radiating from a diaphragm is forced through a phase plug to a smaller opening (i.e. compressed) at the throat, or beginning, of the horn expansion. See: Phase Plug Cone A cone-shaped diaphragm of a loudspeaker that vibrates and radiates sound. Loosely used to describe all diaphragms, some of which have other profiles, such as domes. Constant Directivity Horn A horn design that has a relatively constant angular dispersion of sound over its useful frequency range. Convergence In front or rear projection devices using combined red, green and blue images to form the final picture, it is necessary that all three be perfectly aligned, or converged, with each other in order to maximize the sharpness and color accuracy of the picture. It may be necessary to converge the pictures at many locations all over the picture area. A special test signal is used. Critical Band In hearing perception, it is a band, or range, of frequencies over which the ears tend to combine sounds for purposes of detection or loudness perception. It is not the frequency resolution of hearing, as it relates to the perception of timbre, which is much higher. Critical Distance The distance from a sound source in a room at which the direct sound and the reverberant sound are equal in level. Crossover Electrical filters that direct the appropriate frequencies to the woofer, midrange, tweeter, etc. in a loudspeaker system. The crossover frequency is the frequency at which the loudspeaker driver being turned off (e.g. a woofer) is at the same sound level as the one being turned on (e.g. a tweeter). Crossover Frequency See crossover. Crossover Slope The rate, expressed in dB per octave, at which audio signals are attenuated as frequencies move into the crossover range. A high attenuation rate, e.g. 24 dB/octave means that there is little interaction between adjacent loudspeaker drivers. Low attenuation rates, e.g. 6 dB/octave allow adjacent drivers to operate simultaneously over a wide frequency range. See: Crossover, Octave. Crosstalk Unwanted sound from one channel that leaks into another. CRT An abbreviation for cathode ray tube. A device in which a finely focused beam of electrons scans the phosphor coated front surface of a picture tube causing changes in brightness according to the current flow in the beam. Multiple beams can energize different colored phosphors for color video displays. Used in direct view televisions and projection units. Curvilinear Cone A diaphragm with a reducing curvature from center to edge, used to achieve specific performance objectives. cycles per second The frequency at which a periodic event, such as alternating current, occurs. Now called Hertz, abbreviated Hz.