CAT-5 (Category 5) This is a copper wire standard used in digital networks most commonly Ethernet. It uses an RJ-45 plug and 4 pair wire.  It is suitable for use in 10 Base-T and 100 Base-T Ethernet networks.

CCIR (International Radio Consultative Committee) A branch of the International Telecommunications Union (ITU), a specialized agency of the United Nations - thus the CCIR is a treaty organization related directly to the UN. The CCIR is concerned with generating documents dealing with the preparation, transmission, and reception of all kinds of information using radio signals, with the term "radio" being taken in the broadest sense, including television and telephony.

CCITT (International Telephone and Telegraph consultative Committee) See ITU-T

CD (compact disc) Trademark term for the Sony-Philips digital audio optical disc storage system. The system stores 75 minutes (maximum) of digital audio and subcode information, or other non-audio data, on a 12-centimeter diameter optical disc. The disc is made of plastic, with a top metallized layer, and is read by reflected laser light. Variations (such as the 3" disc) are used for special applications.

CD-R (compact disc-recordable) A compact disc that is recordable at least once.

CD-ROM (compact disc read-only memory) A method of storing digitally coded information, such as computer information or database, on a 12-centimeter diameter optical disc that can be read but not altered.

CD-V (compact disc video) A system storing five minutes of analog video and digital audio plus twenty minutes of digital audio only on a 12-centimeter diameter optical disc, and longer times on 20- or 30-centimeter diameter optical discs.

center frequency One of the parameters of a bandpass filter. The center frequency occurs at the maximum or minimum amplitude response for Butterworth filters, the most common found in audio electronics.

Channel A channel is generally thought of as a separate path through which signals can flow.  (1) In radio and television, a channel is a separate incoming signal or program source that a user can select.  (2) In the public switched telephone network (PSTN), a channel is one of multiple transmission paths within a single link between network points. For example, the commonly used (in North America) T-carrier system line service provides 24 64 Kbps channels for digital data transmission.  (3) In optical fiber transmission using dense wavelength-division multiplexing (DWDM), a channel is a separate wavelength of light within a combined, multiplexed light stream.

checksum The sum of a group of data items used for error checking. If the checksum received equals the one sent, all is well. Otherwise, the receiving equipment requests the data be sent again.

chromatic scale Music. A scale consisting of 12 semitones.

chrominance The color portion of the video signal - includes hue and saturation information but not brightness (see luminance).

class-A An amplifier class

clock A timing device that generates the basic periodic signal used as a source of synchronizing signals in digital equipment.

CLR (Common Language Runtime) Microsoft .NET's equivalent of the Java Virtual machine

CLV (constant linear velocity) A disc rotating at varying numbers of revolutions per second to maintain a constant relative velocity between pickup and track across the disc radius. The CD is a CLV system rotating from 500 rpm (lead-in track) to 200 rpm (lead-out track).

coaxial cable A single copper conductor, surrounded with a heavy layer of insulation, covered by a surrounding shield and jacket. A constant-impedance unbalanced transmission line.

CobraNet™ A trademark of Peak Audio identifying their licensed networking technology used for the deterministic and isochronous transmission of digital audio, video, and control signals over 10 Mbit and 100 Mbit Ethernet networks.

Codec (code-decode) A device for converting video and voice signals from analog to digital for use in digital transmission schemes, and then converting them back again. Most codecs employ proprietary coding algorithms for data compression.

compander A contraction of compressor-expander. A term referring to dynamic range reduction and expansion performed by first a compressor acting as an encoder, and second by an expander acting as the decoder. Normally used in RF wireless applications for noise reduction or headroom reasons.

complex number Mathematics. Any number of the form a + bj, where a and b are real numbers and j is an imaginary number whose square equals -1; and a represents the real part (e.g., the resistive effect of a filter, at zero phase angle) and b represents the imaginary part (e.g., the reactive effect, at 90 degrees phase angle).

composite video A video signal combining luminance, chrominance, and synchronization data in a single signal.  Often connected between equipment on a single coax cable using RCA connectors and color-coded yellow.

compression 1. An increase in density and the resulting decrease in size or magnitude in a medium. 1.the momentary increase in air pressure, caused by the passage of a sound wave. 2. The change in the relative magnitude (peak volume) of and audio signal after processing by a compressor. 3. A reduction in the total digital size of a signal to accommodate cost-effective digital transmission or storage. see also codec.

compression ratio A compression ratio usually expressed as i.e. 5:1, refers to the size of the original data versus the size after compression by a codec.  If the data has been reduced to one-fifth the original size, the compression ratio is 1:5.

compression wave A wave propagated by means of the compression of a fluid, such as a sound wave in air.

compressor A signal processing device used to reduce the dynamic range of the signal passing through it. For instance, an input dynamic range of 110 dB might pass through a compressor and exit with a new dynamic range of 70 dB. This clever bit of skullduggery is normally done through the use of a VCA (voltage controlled amplifier), whose gain is a function of a control voltage applied to it. Thus, the control voltage is made a function of the input signal's dynamic content.

condenser microphone A microphone design where a condenser (the original name for capacitor) is created by stretching a thin diaphragm in front of a metal disc (the backplate). By positioning the two surfaces very close together an electrical capacitor is created whose capacitance varies as a function of the movement of the diaphragm in response to varying sound pressure. Any change in sound pressure causes the diaphragm to move, which changes the distance between the two surfaces. If the capacitor is first given an electrical charge (polarized) then this movement changes the capacitance, and if the charge is fixed, then the backplate voltage varies proportionally to the sound pressure. In order to create the fixed charge, condenser microphones require external voltage (polarizing voltage) to operate. This is normally supplied in the form of phantom power from the microphone preamp or the mixing console.

constant-Q equalizer (also constant-bandwidth) Term applied to graphic and rotary equalizers describing bandwidth behavior as a function of boost/cut levels. Since Q and bandwidth are inverse sides of the same coin, the terms are fully interchangeable. The bandwidth remains constant for all boost/cut levels.

critical band Physiology of Hearing. A range of frequencies that is integrated (summed together) by the neural system, equivalent to a bandpass filter (auditory filter) with approximately 10-20% bandwidth (approximately one-third octave wide). [Although the latest research says critical bands are more like 1/6-octave above 500 Hz, and about 100 Hz wide below 500 Hz.] The ear can be said to be a series of overlapping critical bands, each responding to a narrow range of frequencies. Introduced by Fletcher (1940) to deal with the masking of a pure-tone by wideband noise.

crossfade Within the audio industry, a term most often associated with dj mixers. DJ mixers usually feature a crossfader slide-type potentiometer control. This control allows the dj to transition from one stereo program source (located at one travel extreme) to another stereo program source (located at the other travel extreme). The goal in crossfader design is to maintain equal loudness (power) in the system during transition.  Contrast with pan and balance controls.

crossover An electrical circuit (passive or active) consisting of a combination of high-pass, low-pass and bandpass filters used to divide the audio frequency spectrum (20 Hz - 20 kHz) into segments suitable for individual loudspeaker use.  Named from the fact that audio reproduction transitions (or crosses over) from one driver to the next as the signal increases in frequency. For example, consider a two driver loudspeaker crossed over at 800 Hz: Here only one driver (the woofer) works to reproduce everything below 800 Hz, although both drivers work reproducing the region immediately around 800 Hz (the crossover region), only the last driver (the tweeter) works to reproduce everything above 800 Hz. Crossover circuits are characterized by their type (Butterworth, Bessel and Linkwitz-Riley being the most popular), and by the steepness of their roll-off slopes (the rate of attenuation outside their passbands) as measured in decibels per interval, such as dB/octave.

crosstalk (magnetic) See: print-through

CRT (Cathode Ray Tube ) Common electronic "pitcher tube" used in television receivers and computer monitors.

Cue 1. A term found throughout various audio fields meaning to monitor, or listen (via headphones) to a specific source. In mixers (particularly dj mixers) the term is used interchangeably with solo or PFL as found on recording consoles. 2. A gesture by a conductor signaling the entrance of a performer or part. 3. A signal, such as a word or an action, used to prompt another event in a performance, such as an actor's speech or entrance, a change in lighting, or a sound effect.

current Symbol i, I Electricity. a. A flow of electric charge. b. The amount of electric charge flowing past a specified circuit point per unit time, or the rate of flow of electrons.

current loop A data transmission scheme that looks for current flow rather than voltage levels. This systems recognizes no current flow as a binary zero, and having current flow as a binary one. Favored for its low sensitivity to cable impedance, and independence of a common ground reference; hence current loops do not introduce ground loops. MIDI is an example of a current loop interconnect system.

cut-only equalizer Term used to describe graphic equalizers designed only for attenuation. (Also referred to as notch equalizers, or band-reject equalizers). The flat (0 dB) position locates all sliders at the top of the front panel. Comprised only of notch filters (normally spaced at 1/3-octave intervals), all controls start at 0 dB and reduce the signal on a band-by-band basis. Proponents of cut-only philosophy argue that boosting runs the risk of reducing system headroom.

cutoff frequency Filters. The frequency at which the signal falls off by 3 dB (the half power point) from its maximum value. Also referred to as the -3 dB points, 3 dB down points or the corner frequencies.