C The electronic symbol for a capacitor.
C50 (dB); C80 (dB) Intelligibility. Clarity ratings; a logarithmic measure of the early-to-late arrival sound energy ratio; for music the constant is 80 ms (C80) and for speech it is 50 ms (C50). Compare with D50 (%).
CABA (Continental Automated Buildings Association) An industry association that promotes advanced technologies for the automation of homes and buildings in North America.
cables Audio systems use many different types of cables (for all the details see Lampen):
fiber optics The technology of using glass fibers to convey light and modulated information. Short distances (typically less than 150 feet) use plastic fibers, while long distances must use glass fibers.
mic cable (aka audio cable) A shielded twisted-pair, usually designed for low current, high flexibility and low handling noise. The best insulating materials are somewhat inflexible, so most mic cables use rubber, neoprene, PVC, or similar materials, with small gauge wire, and therefore, true mic cables are not intended for long runs. Unfortunately the term "mic cable" has become synonymous with general-purpose audio cable (as distinguished from speaker cable) when it can be quite different. The very best audio cable may not be the best mic cable and vice versa.
quad mic cable or star-quad mic cable [a term coined by Canare for the first quad mic cable, but was not trademarked and is now a generic term]. A four-conductor cable exhibiting very low noise and hum pickup (hum reduction can be 30 dB better than standard mic cable). The four conductors are wound together in a spiral, and then opposite conductors are joined together at the connectors forming a two-conductor balanced line (also called double balanced) with superior performance.
speaker cable An unshielded insulated pair, normally not twisted, characterized by heavy (or large) gauge conductors (hence, low-resistance), used to interconnect the output of a power amplifier and the input of a loudspeaker. The coupling between amplifier and loudspeaker may be direct or via transformer (see constant voltage). The star quad design described above also makes excellent speaker cables for use in high noise environments.
triax cable Similar to coax, but with an extra layer of insulation and a second conducting sheath, providing better bandwidth and RFI rejection -- for a price.
twisted-pair Standard two-conductor copper cable, with insulation extruded over each conductor and twisted together. Usually operated as a balanced line connection. May be shielded or not, abbreviated UTP (unshielded twisted-pair), or STP (shielded twisted-pair).
cacophony 1. Jarring, discordant sound; dissonance: heard a cacophony of horns during the traffic jam. 2. The use of harsh or discordant sounds in literary composition, as for poetic effect. [AHD]
cadence Music. A progression of chords moving to a harmonic close, point of rest, or sense of resolution. [AHD]
CAF (Common Amplifier Format) Power Amplifiers. A testing and specification protocol developed by Pat Brown (SynAudCon) for creating an open data base for all sound contractors and other users of power amplifiers that allows direct comparisons between apples and apples.
calcium light See: limelight.
CALM (Commercial Advertisement Loudness Mitigation) Act Federal legislation regulating the loudness of commercials relative to program material, ensuring they are the same level.
calypso Music. A type of music that originated in the West Indies, notably in Trinidad, and is characterized by improvised lyrics on topical or broadly humorous subjects. [AHD]
Campbell, George A. (1870-1954) American engineer who was one of the pioneers in long-distance telegraphy and telephony, and in that position created the first audio filter/bandpass EQ circuit. See: U.S. Patent 1,227,113 Electric Wave-Filter issued May 22, 1917. Also see: Wave-Filter.
Candombe Musical Instrument. Uruguay drum music.
Cannon plug See connectors.
canola (Canada oil low acid) A rapeseed oil that is very low in erucic acid content and high in monounsaturated fatty acids. [AHD]
cans See headphones.
capacitive reactance See impedance.
capacitor Circuit symbol: C. 1. A device with the primary purpose of introducing capacitance into an electric circuit. 2. An element within a circuit consisting of two conductors, each with an extended surface exposed to that of the other, but separated by a layer of insulating material called the dielectric. Note: The dielectric is designed so the electric charge on one conductor is equal in value but opposite in polarity to that of the other conductor. [IEEE]
capacitor microphone See condenser microphone.
capacitor standard values See values.
capo A small movable bar placed across the fingerboard of a guitar or similar instrument so as to raise the pitch of all the strings uniformly. [AHD]
carat See: karat.
carborundum A trademark for an abrasive of silicon carbide crystals. [AHD] [This trademark dates back to 1905.]
cardinal number 1: a number (as 1, 5, 15) that is used in simple counting and that indicates how many elements there are in an assemblage. 2: the property that a mathematical set has in common with all sets that can be put in one-to-one correspondence with it. [MWD]
cart Radio Broadcast. NIckname for the Fidelipac.
Cartesian coordinate system 1. A two-dimensional coordinate system in which the coordinates of a point in a plane are its distances from two perpendicular lines that intersect at an origin, the distance from each line being measured along a straight line parallel to the other. [AHD] 2. A three-dimensional coordinate system in which the coordinates of a point in space are its distances from each of three perpendicular planes that intersect at an origin. After the Latin form of Descartes, the mathematician who invented it.
cascade Electronics. A series connected string of two or more circuits where the output of one circuit drives the input of the next, etc.
cassette (or compact cassette) A small flat case containing two reels and a length of magnetic tape that winds between them, often used in audio and video recorders and players and as a medium for storing data in digital form. [AHD] First developed by Philips in 1962.
Category wiring A wire grading system developed by the EIA / TIA ("TIA/EIA 568-B: Commercial Building Telecommunications Cabling Standard") describing UTP cabling (and hardware) with transmission characteristics. Some of the most popular follow:
CAT 3 (Category 3 cable) Unshielded twisted-pair (UTP) data grade cable (usually 24 AWG). CAT 3 cables are characterized to 16 MHz and support applications up to 10 Mbps. Typically used for voice telephone and 10Base-T Ethernet systems.
CAT 5 (Category 5 cable) Unshielded twisted-pair (UTP) data grade cable (usually 24 AWG). CAT 5 cable runs are limited to 100 meters (328 feet) due to signal radiation and attenuation considerations. Longer runs are vulnerable to electromechanical interference. CAT 5 cables are characterized to 100 MHz and support applications up to 100 Mbps. Most common application is 100Base-T Ethernet systems. [With the release of ANSI/TIA/EIA-568-B, CAT 5 is no longer recognized and is officially replaced by CAT 5e (see next entry).]
CAT 5e (Category 5 enhanced) As above CAT 5 cable except there is a plastic rib running through the center of the cable that separates the pairs, maintaining greater distance between them to reduce crosstalk (there are other non-rib ways to meet this requirement). It also keeps them in position to maintain the proper geometry along the whole cable. It uses better insulation, making attenuation and crosstalk performance better. IT DOES NOT EXTEND THE BANDWIDTH. The rated bandwidth is the same 100 MHz. It may run faster but the official specification (ANSI/TIA/EIA-568-B) does not require it, so caveat emptor.
CAT 6 (Category 6) Same as CAT 5e except with extended bandwidth to 250 MHz.
CAT 7 (Category 7) Same as CAT 6 except with extended bandwidth to above 600 MHz.
catenary Mathematics. The curve formed by a perfectly flexible, uniformly dense, and inextensible cable suspended from its endpoints. It is identical to the graph of a hyperbolic cosine. [AHD] The cable used by Nik Wallenda in his 2012 crossing of Niagara Falls formed a catenary, causing him to first walk downhill then back uphill.
caterwaul A shrill, discordant sound. [AHD]
cathode follower See buffer amplifier.
cat organ (katzenklavier in German) A mythical (hopefully) device using cat's screeching sounds to produce "music."
Cauer filters See elliptic filters.
CAV (constant angular velocity) A disc rotating at a constant number of revolutions per second. The LP is a CAV system at 33-1/3 rpm. Another example is the CAV laser disc that plays two 30-minute sides.
CBID (content-based identification) The method of establishing intellectual property through a system that does not embed digital watermarks into the audio data but instead uses algorithms to analyze an audio segment to determine its unique characteristics (e.g., loudness, pitch, brightness and harmonicity).
CBN (common-bonded network) See mesh ground.
CCIF (Comité Consultatif International des Téléphonique, or International Telephone Consultative Committee) The CCIF merged with the CCIT becoming the CCITT. In 1992, the CCITT, together with the CCIR, morphed into the ITU.
CCIR (Comité Consultatif International des Radio Communications, or International Radio Consultative Committee) (International Radio Consultative Committee) Merged with the ITU and became the ITU-R radiocommunications division.
CCIR ARM See weighting filters.
CCIR-468 See weighting filters.
CCIR 2 kHz See weighting filters.
CCITT (Comité Consultatif International des Téléphonique et Télégraphique, or International Telegraph and Telephone Consultative Committee) Merged with the ITU and became the ITU-T telecommunications division.CCWLE (counterclockwise lead end) Refers to electric motor rotation viewed from the end where the hook-up wires exit.
CD (compact disc) Trademark term for the Sony-Philips digital audio optical disc storage system. The system stores 80 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 reserved for special applications. Interesting history found here. [Historical Note: The modern CD is based on James Russell's original work, while at Bettelle Memorial Institute's Northwest laboratory. He is acknowledged as the inventor of optical data storage where he developed the first digital-to-optical recording and playback system in 1970. In 1985 he began licensing his technology to Sony, Philips and others who bought the manufacturing rights and begun mass production. Russell was born in Bellingham, Washington.]
CD-4 (Compatible Discrete 4) also called Quadradisc (No connection to "compact disc" above). JVC introduced this discrete quadraphonic vinyl record in 1971. This was the only successful discrete 4-channel record, although short lived.
CD horn EQ See constant directivity horn.
CD-I (compact disc interactive) System storing digital audio, video, text, and graphics information interactively, with user control over content and presentation, on a 12-centimeter diameter optical disc.
CD+MIDI A System storing MIDI information in a disc's subcode area.
CD-PROM (compact disc programmable read-only memory) A write-once CD-ROM disc.
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.
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.
CdS (cadmium sulfide) 1. Chemistry. Known as greenockite in its only native form, it is a naturally occurring light-variable resistor (see LDR). 2. Art & Color. A yellow powder that is used as a pigment. Also of interest: Cadmium Sulfide vs. Silicon.
CEA (Consumer Electronics Association) CEA's mission is to grow the consumer electronics industry.
CEA-2006 Testing & Measurement Methods for Mobile Audio Amplifiers A voluntary standard published by the CEA advocating an objective and uniform method for determining a car (or other mobile) amplifier's power rating. It specifies that the power be measured with a supply voltage of 14.4 volts, a 4-ohm resistive load, at a 1% THD+N level, and a frequency range of 20 Hz - 20 kHz. Also that S/N be measured using an A-weighted filter at a reference level of 1 watt into 4 ohms.
CEDIA (Custom Electronic Design & Installation Association) A global trade association of companies that specialize in planning and installing electronic systems for the home.
CEI (Commission Electrotechnique Internationale) See IEC.
Celsius Abbr. C Of or relating to a temperature scale that registers the freezing point of water as 0 °C and the boiling point as 100 °C, under normal atmospheric pressure. [AHD] (The term "Celsius" is preferred to "centigrade" in technical contexts.) [After Anders Celsius]
Celsius, Anders (1701-1744) Swedish astronomer who devised the centigrade thermometer (1742). [AHD]
CEMA (Consumer Electronics Manufacturers Association) The definitive source for information about the consumer electronics industry.
CE-mark(Conformité Européenne) The letter-logo used in marking units certified for distribution within the European Union (EU) that meet the directives mandated by the European Commission.
censor DJ Software Technology. A censor button masks parts of a song, i.e., it is a quick reverse with no timing loss. With a censor button you can reverse a section without losing play position.
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.
centi- Prefix for one hundredth (10-2), abbreviated c.
centigrade Temperature term generally not used in scientific contexts apart from meteorology. See Celsius.
cepstrum The word "spectrum" with the first four letters reversed. Created in 1963 by Bogert, Healy and Tukey in their paper "The Quefrency Analysis of Time Series for Echoes: Cepstrum, Pseudoautocovariance, Cross-Cepstrum, and Saphe Cracking." They observed that the logarithm of the power spectrum of a signal containing an echo has an additive periodic component due to the echo, and thus the Fourier transform of the logarithm of the power spectrum should exhibit a peak at the echo delay. They called this function the "cepstrum," interchanging letters in the word spectrum because "in general, we find ourselves operating on the frequency side in ways customary on the time side and vice versa." The cepstrum is obtained in two steps: A logarithmic power spectrum is calculated and declared to be the new analysis window. On that an inverse FFT is performed. The result is a signal with a time axis.
cereal interface A bowl and a spoon. [Thanks PM.]
Chalice drum See: goblet drum.
Chandler Circle or Chandler Wobble Astronomy. The earth wobbles slightly and causes the North Pole to shift about a bit. Here is a great description: "If the North Pole were a scribing stylus, it would trace a line every 428 days in the shape of an irregular circle, with a diameter varying from 25 to 30 feet. Over the year, these irregular circles would all fall within an area some 65 feet across, called the Chandler Circle. The average position of the center of this circle is the Geographic North Pole." Barry Lopez, Arctic Dreams: Imagination and Desire in a Northern Landscape, New York: Bantam, 1986, pp 16-20.
channel separation See crosstalk.
chanteuse A woman singer, especially a nightclub singer. [AHD]
Chapman Stick® Musical Instrument. A two-handed fretboard tapping instrument invented by Emmett Chapman in 1969.
charge Symbol q 1. Electricity. a. To cause formation of a net electric charge on or in (a conductor, for example). b. To energize (a storage battery) by passing current through it in the direction opposite to discharge. 2. Physics. a. The intrinsic property of matter responsible for all electric phenomena, in particular for the force of the electromagnetic interaction, occurring in two forms arbitrarily designated negative and positive. b. A measure of this property. c. The net measure of this property possessed by a body or contained in a bounded region of space. [AHD]
chassis ground 1. The common point on a conducting chassis surrounding the system electronic circuit boards; usually separate from the signal ground but may be tied at one point. 2. The earth grounding connection provided on the chassis for safety reasons. See the RaneNote Sound System Interconnection.
Chebyshev filter A class of electronic filter characterized by having an equiripple magnitude response, meaning the magnitude increases and decreases regularly from DC to the cutoff frequency. Chebyshev filters are classified by the amount of ripple in the passband, for example a 1 dB Chebyshev low-pass filter is one with a magnitude response ripple of 1 dB. Chebyshev filters are popular because they offer steeper roll-off rates than Butterworth filters for the same order, but for audio applications the Chebyshev is virtually never seen due to the superior magnitude and phase responses of the Butterworth class. [After Pafnuty Lvovich Chebyshev.]
Chebyshev, Pafnuty Lvovich [also spelled Tschebyscheff and Tchebysheff] (1821-1894) Russian mathematician best remembered for his work on the theory of prime numbers. [AHD]
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.
Chess, Leonard (birth name: Lejzor Czyz) (1917-1969) Founder of Chess Records famous for his development of electric blues and discovering and promoting such talents as Muddy Waters, Bo Diddley, Chuck Berry and Etta James.
chiasmus The term for a reversal in the order of words in two otherwise parallel phrases. For example, the advice from the great sci-fi writer Ray Bradbury to aspiring writers: "You have to know how to accept rejection and reject acceptance," or the familiar adage: "Say what you mean and mean what you say."
chiff The name given to the burst of white noise at the beginning of a note (like the "ch" sound in the word "chiff") that occurs in a pipe organ or whistle. Also the hissy white noise heard throughout a note's duration from a whistle.
chilihedron Geometry. A solid figure or object with a thousand plane faces. [OED]
Chinese string instruments Go here.
chirogymnast Music. A mechanical apparatus for the exercising of a pianist's fingers. [Kacirk]
chirp A short, high-pitched sound, such as that made by a small bird or an insect. [AHD] An electronic chirp (swept sine wave) is used in acoustic testing. See for example: Sine Chirps for Measuring Impulse Response by Ian Chan, Stanford Research Systems.
Chitlin' circuit Term for the black music scene primarily in the '30s and '40s. See: Preston Lauterbach, The Chitlin Circuit and the Road to Rock ’N’ Roll
chopper Slang for any type of SMPS device.
chopper-stablized op amp Electronics. A specialized op amp where the input errors associated with offset voltage, bias current, temperature drift and 1/f noise are constantly corrected,.
chordophone Generic term for instruments that produce their sound by means of strings stretched between fixed points. Chordophones form one of the four main classes instruments. [Sadie] See: aerophone, idiophone, membranophone.
chorusing Recording. An effect where the audio signal is given multiple delays so as to sound like several instruments playing at once. The delay times are short, typically 20-45 milliseconds, and each delayed signal may be pitch-shifted. The effect is similar to hearing a "chorus," where everyone is singing the same thing but at slightly different times and pitches. Chorusing is a slightly elaborated version of doubling. A signal is delayed approximately 15-35 milliseconds and mixed with the undelayed signal. The delay time is modulated by a low-frequency-oscillator to achieve a shimmering effect due to a combination of beat-frequencies and the slight pitch-bending that occurs as the delay time is changed.
Christie, Samuel Hunter See Wheatstone bridge.
chrominance 1. Abbreviated C. The color portion of the video signal - includes hue and saturation information but not brightness. 2. VJ Jargon. A video filter that rejects color portions of an image. Used by VJs to eliminate or feature specific image colors. Popular technique for blending images. See luminance.
Chronophone (aka Gaumont Chronophone) Apparatus patented by Léon Gaumont in 1902 for synchronizing sound and film. Wonderful photos here. Consisting of two turntables which were switched by an operator when one finished playing so as to create a seamless soundtrack, thus reminiscent of a DJ mixer crossfader. More photos and detail here.
Chrysler Air Raid Siren Promoted as "The Most Powerful Siren Ever Built," now a much sought after collector's item. Powered by a 180 HP V-8 Chrysler Hemi® gasoline engine driving a three-stage compressor blowing 2,610 cubic feet of air a minute into a giant siren rotor, with exit velocity of 400 miles per hour, the siren produced loudness levels of 138 dB SPL at a distance of 100 feet. Hit the link to hear a sample. [Impressive. Thanks Rob!]
Chula Dance. A Portuguese folk dance.
CI (cochlear implant) A hearing assisting device surgically placed in the inner ear that allows a representation of sounds.
Çigirtma Ancient Turkish folk instrument made from the wing bone of the mountain eagle, now endangered.
circuit-bending The popular art of altering low-cost electronic devices -- toys mostly -- to make them produce new and unique sounds such as squawks, beeps and bongs, thus creating a homemade musical instrument. Reed Ghazala is credited with inventing this new music genre.
circumaural Headphones. Literally "around the ear," thus headphones with earpieces surrounding the ear and pressing against the side of the head, forming a seal to reduce ambient noise leakage. Compare with supra-aural.
CIS (Common Intelligibility Scale) International standard (IEC 60849) that maps all intelligibility tests to a common scale for comparative results.
CISAC (Confederation Internationale des Societes d'Auterus et Compositeurs or The International Confederation of Societies of Authors and Composers) An organization that works towards increased recognition and protection of creator's rights.
CISC (complex instruction set computing) See RISC.
CISPR (Comite International Special des Perturbations Radioelectriques or International Special Committee on Radio Interference) Established in 1934 by a group of international organizations to address radio interference.
cittern Musical Instrument. A 16th-century guitar with a flat, pear-shaped body. [AHD]
Clair, Walter Eugene ("Gene") (1940-2013) American engineer, entrepreneur, and live sound mixer, who cofounder the famous touring sound company, Clair Brothers, with his brother, Roy in 1966.
clairaudience The supposed power to hear things outside the range of normal perception. [AHD] Also called aural hallucinations.
clamor Loud, usually sustained noise, as a public outcry of dissatisfaction. [AHD]
clapperboard The device used to synchronize sound and picture in film and video making, consisting of two boards that bang together and are viewed by the camera to create a picture and sound reference point. Named for the sharp "clap" sound made when the boards are struck together.
claque 1. A group of persons hired to applaud at a performance. 2. A group of fawning admirers. [AHD]
clarion Music. 1. A medieval trumpet with a shrill clear tone. 2. The sound of this instrument or a sound resembling it. [AHD]
clarity index or clarity measure See C50 (dB).
class-A An amplifier class.
Class 1, 2 & 3 wiring See: wiring classes.
Class I equipment Equipment where protection against electric shock does not rely on basic insulation only, but also provides an additional safety precaution allowing connection of the equipment to the protective earth conductor in the fixed wiring of the installation so that accessible metal parts cannot become live in the event of a failure of the basic insulation.
Class II equipment Equipment where protection against electric shock does not rely on basic insulation only, but also provides additional safety precautions such as double insulation or reinforced insulation, but there is no provision for connection of the equipment to the protective earth conductor.
class-compliant Refers to USB devices that automatically work with both Apple (Mac or iOS) and PC (Windows) devices without the need to install proprietary drivers, providing true plug-and-play performance.
CLF (Common Loudspeaker data sheet Format) Loudspeakers. The organization developed a common format for the presentation of loudspeaker data, which also serves as a stand-alone specification sheet for the loudspeaker parameters required by system designers, with a free downloadable data viewer program.
client 1. Any device connected to a server on a local area network (LAN), e.g., personal computer, DSP-based unit, workstation, etc. It is a computer program that requests a service from the server program, usually over the network, e.g. a Wi-Fi card is a client in a WLAN.
clipping Term used to describe the result of an amplifier running into power supply limitation. The maximum output voltage that any amplifier can produce is limited by its power supply. Attempting to output a voltage (or current) level that exceeds the power supply results in a flat-toping effect on the signal, making it look cut off or "clipped." A clipped waveform exhibits extreme harmonic distortion, dominated by large amplitude odd-ordered harmonics making it sound harsh or dissonant. Hard clipping is the term used to describe extreme clipping of a signal, producing highly visible flat-toped waveforms as viewed on an oscilloscope; soft clipping refers to moderate clipping that results in waveforms having softly-rounded edges, as opposed to the sharp edges of hard clipping. For how-to-avoid see the RaneNote Setting Sound System Level Controls.
clock A timing device that generates the basic periodic signal used as a source of synchronizing signals in digital equipment.
cloud computing Technology that allows accessing vast memory storage or hugh software remotely from a computer via the Internet. The computer being the usual desktop or laptop, or hidden inside a smartphone, tablet or other smart device. One audio application is to have all your music stored on the Internet instead of on your hard drive, giving you pretty much limitless capacity and accessible anywhere by any Internet capable device.
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). Another example is the CLV laser disc that plays two sixty minute sides.
CMR or CMRR See common-mode rejection (ratio).
coaxial Having or mounted on a common axis. [AHD]
coaxial cable A single copper conductor, surrounded with a heavy layer of insulation, covered by a thick surrounding copper shield and jacket. A constant-impedance unbalanced transmission line. See cables.
coaxial loudspeaker Two or more transducers sharing a common axis. A common example is the car speaker with a small tweeter mounted on axis and in front of the woofer cone. See Frazier white paper for in-depth details.
CobraNet® A registered trademark of Cirrus Logic identifying their licensed networking technology used for the deterministic and isochronous transmission of digital audio, video, and control signals over Ethernet networks.
cochlea A spiral-shaped cavity of the inner ear that resembles a snail shell and contains nerve endings essential for hearing. [AHD]
cochlear implant See: CI.
codec (code-decode also compression-decompression) Originally a device for converting voice signals from analog to digital for use in digital transmission schemes, normally telephone based, and then converting them back again. Broaden now to mean an electronic device that converts analog signals, such as video and voice signals, into digital form and compresses them to conserve bandwidth. Many codecs employ proprietary coding algorithms for data compression, common examples being Dolby's AC-2, ADPCM, and MPEG schemes. It is data compression (and direct digital video & audio inputs) that evolved the meaning of compression-decompression, however today the marketplace offers both compressed and uncompressed versions based on the application.
coercivity Recording. A measure of the difficulty of erasure in magnetic recording.
coincident-microphone technique See X/Y microphone technique.
column array See: line arrays.
comb filter Acoustics. A frequency response curve that resembles a comb, having steep peaks and valleys, caused by reflections arriving out of phase with the direct sound, creating reinforcements and cancellations of the sound. [Hit the link to read about signal processing comb filters.]
Common Amplifier Format See: CAF.
common logarithm A logarithm based on the powers of 10 (aka base-10).
common-mode rejection (ratio) Abbr. CMR and CMRR The characteristic of a differential amplifier to cancel all common-mode signals applied to its inputs. The "ratio" is obtained by dividing the input common-mode voltage by the amount of output voltage, thereby giving you some measure of the amplifier's ability to reject common signals. See the RaneNote Audio Specifications.
common-mode signal Strictly speaking it is the average of the signals present at the two inputs of a differential amplifier, although it is more often meant to be the voltage level present at both inputs, as if they were tied together.
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 for noise reduction or headroom reasons.
comparator Electronics. A circuit element with two inputs labeled positive and negative and one output. The output goes either high or low depending upon which input is greater. If the positive input is greater than the negative input then the output goes high, and vice versa. Also see Schmitt trigger.
complex frequency variable An AC frequency in complex number form. See complex number.
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 [AHD]; 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).
complex separation "The theory that, in music, a song gets only one chance to make a first impression. After that the brain starts breaking it down, subdividing the musical experience into its various components -- lyrical, melodic and so forth." [A Dictionary of the Near Future by Douglas Coupland, NY Times, September 12, 2010.]
component video A video system for color television that stores separate channels of red, green and blue. Becoming increasingly popular on DVD players, as well.
compression driver Loudspeakers. A high frequency dynamic loudspeaker that mounts at the rear of an acoustic horn that further amplifies and greatly improves the overall efficiency. First commercial units where developed in 1926 by Western Electric and engineers Wente and Thuras.
compression wave A wave propagated by means of the compression of a fluid, such as a sound wave in air. [AHD]
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. [Long answer: What "compression" is and does has evolved significantly over the years. Originally compressors were used to reduce the dynamic range of the entire signal; with modern advances in audio technology, compressors now are used more sparingly. First the classical case: The history of compressors dates back to the late '20s and '30s (the earliest reference I have located is a 1934 paper in the Bell Labs Journal.) The need arose the very first time anyone tried to record (sound-motion pictures film recording, phonograph recording, etc.) or broadcast audio: the signal exceeded the medium. For example, the sound from a live orchestra easily equals 100 dB dynamic range. Yet early recording and broadcasting medium all suffered from limited dynamic range. Typical examples: LP record 65 dB, cassette tape 60 dB (w/noise reduction), analog tape recorder 70 dB, FM broadcast 60 dB, AM broadcast 50 dB. Thus "6 pounds of audio into a 4 pound bag" became the necessity that mothered the invention of the compressor (sorry). Early compressors did not have a "threshold" knob, instead, the user set a center ("hinge") point equivalent to the midpoint of the expected dynamic range of the incoming signal. Then a ratio was set which determined the amount of dynamic range reduction. The earlier example of reducing 110 dB to 70 dB requires a ratio setting of 1.6:1 (110/70 = 1.6). The key to understanding compressors is to always think in terms of increasing and decreasing level changes in dB about some set-point. A compressor makes audio increases and decreases smaller. From our example, for every input increase of 1.6 dB above the hinge point, the output only increases 1 dB, and for every input decrease of 1.6 dB below the hinge point, the output only decreases 1 dB. If the input increases by x-dB, the output increases by y-dB, and if the input decreases by x-dB, the output decreases by y-dB, where x/y equals the ratio setting. Simple -- but not intuitive and not obvious. This concept of increasing above the set-point and decreasing below the set-point is where this oft-heard phrase comes from: "compressors make the loud sounds quieter and the quiet sounds louder." If the sound gets louder by 1.6 dB and the output only increases by 1 dB, then the loud sound has been made quieter; and if the sound gets quieter by 1.6 dB and the output only decreases by 1 dB, then the quiet sound has been made louder (it didn't decrease as much). Think about it -- it's an important concept. With advances in all aspects of recording, reproduction and broadcasting of audio, the usage of compressors changed from reducing the entire program to just reducing selective portions of the program. Thus was born the threshold control. Now sound engineers set a threshold point such that all audio below this point is unaffected, and all audio above this point is compressed by the amount determined by the ratio control. Therefore the modern usage for compressors is to turn down (or reduce the dynamic range of) just the loudest signals. Other applications have evolved where compressors are used in controlling the creation of sound. For example when used in conjunction with microphones and musical instrument pick-ups, compressors help determine the final timbre by selectively compressing specific frequencies and waveforms. Common examples are "fattening" drum sounds, increasing guitar sustain, vocal "smoothing," and "bringing up" specific sounds out of the mix, etc.] See the RaneNote Dynamics Processors and the RaneNote Signal Processing Fundamentals.
concealment Digital Audio. An interpolation technique where the value of a missing sample is estimated from those nearby.
concert sound See: History of Concert Sound.
condenser Electronics. Old name for a capacitor.
condenser microphone [Also called capacitor microphone but more properly, the correct name is electrostatic microphone.] Invented by Wente in 1916, 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 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.
cone of confusion Hearing. If a sound presented to one ear is within an on-axis cone, then it is not possible to locate it, due to the head blocking the sound from reaching the other ear (or attenuates it so much that the brain ignores it). (The listener can tell from which side the sound comes from but cannot locate it within the cone.) There is a similar effect for sounds occurring exactly in front, or to the rear, where the sound does reach each ear but with the identical level and direction causing localization confusion. If the sound is not heard differently by each ear, we cannot accurately localize the source. This is called the "cone of confusion."
conformal coating Manufacturing. A protective coating applied to electronic components to make them impervious to environmental effects.
conjobble An English word no longer in print (except here) meaning to settle, arrange; to chat (late 17th century).
conjunto Music. A style of popular dance music originating along the border between Texas and Mexico, characterized by the use of accordion, drums, and 12-string bass guitar and traditionally based on polka, waltz, and bolero rhythms. [AHD]
connectionless Networks. Protocols where the host sends messages without establishing connection with the recipients. This is the "hope and pray" school: put the message on the network (with an address) and "hope and pray" it arrives. Examples: Ethernet, and UDP are connectionless.
connection-oriented Networks. Protocols where the host sends messages directly to a connected receiver (as opposed to connectionless above), i.e., the protocol requires a confirmed channel before transmission. TCP/IP is connection-oriented.
banana jack or banana plug A single conductor electrical connector with a banana-shaped spring-metal tip most often used on audio power amplifiers for the loudspeaker wiring. Usually configured as a color-coded molded pair (red = hot & black = return) on 3/4" spacing. Also used for test leads and as terminals for plug-in components. The British still refer to these as a GR plug, after General Radio Corporation, the inventor (according to The Audio Dictionary by Glenn D. White).
binding posts Alternate name for banana jacks above, derived from the capability to loosen (unscrew) the body and insert a wire through a hole provided in the electrical terminal and tighten the plastic housing down over the wire insulation, holding the wire in place.
Cannon connector or Cannon plug Alternate reference for XLR.
Elco connector or Elco plug AVX manufactures several connectors used for interconnecting multiple audio channels at once, most often found in recording studios on analog and digital audio tape machines. One of these, a 90-pin version (Vari*con Series 8016), carries 28 shielded pairs of audio channels, allowing 3-wires per channel (positive, negative & shield) for a true balanced system interconnect.
Euroblocks Shortened form of European style terminal blocks, a specialized disconnectable, or plugable terminal block consisting of two pieces. The receptacle is permanently mounted on the equipment and the plug is used to terminate both balanced and unbalanced audio connections using screw terminals. Differs from regular terminal strips in its plugability, allowing removal of the equipment by disconnecting the plug section rather than having to unscrew each wire terminal. Unofficial, but popularly followed, is the color-code convention where green is used for inputs and orange is used for outputs.
RCA (aka phono jack or pin jack) The Radio Corporation of America (RCA) originally developed this type of unbalanced pin connector for internal chassis connections in radios and televisions during the '30s. It became popular for use in the cables that connected phonograph cartridges to preamplifiers because it was inexpensive and easily fitted to the rather small diameter shielded cables used for the cartridge leads (then they were mono cartridges so single conductor shielded cables were adequate -- now you know). The standard connector used in line-level consumer and project studio sound equipment, and most recently to interconnect composite video signals. (excerpted from Yamaha Sound Reinforcement Handbook, pp. 297-298). The controlling standard is IEC Specification 60603-14.
Speakon® A registered trademark of Neutrik for their original design loudspeaker connector, now considered an industry de facto standard.
terminal strips or terminal blocks Also called barrier strips, a type of wiring connector provided with screwdown posts separated by insulating barrier strips. Used for balanced and unbalanced wiring connections, where each wire is usually terminated with a crimped-on spade- or ring-connector and screwed in place; not disconnectable, or plugable. Has become known as the U.S. style terminal blocks. Contrast with Euroblocks.
1/4" TRS (tip-ring-sleeve) 1. Stereo 1/4" connector consisting of tip (T), ring (R), and sleeve (S) sections, with T = left, R = right, and S = ground/shield. 2. Balanced interconnect with the positive & negative signal lines tied to T and R respectively and S acting as an overall shield. 3. Insert loop interconnect with T = send, R = return, and S = ground/shield. [Think: ring, right, return] The international standard is IEC 60603-11.
Other popular TRS versions are the mini (3.5 mm) and the sub-mini (2.5 mm) found on cell phones, , iPods, MP 3 players, etc. [Note that the 3.5 mm and 2.5 mm sizes are often mistakenly referred to as 1/8" and 3/32″ respectively, but these dimensions are only approximations since 1/8" = 3.18 mm and 3/32" = 2.29 mm.].
Another interesting variant is the TRRS (tip-ring-ring-sleeve) connector commonly found on iPhones, newer model iPods, cell phones and other media players. The extra ring connection is used for microphone audio on cell phone headsets, as well as video on digital cameras, camcorders, and portable DVD players.
XLD A proposed version (by Neutrik) of the standard XLR connector (shown below) that is keyed to prevent digital cables from being connected to analog connectors and vice versa. The original application is for AES3-MIC digital mics, to make them incapable with standard analog mic inputs. [Note: this is not yet in production.]
XLR 1. Originally a registered trademark of ITT-Cannon in 1958. The original model number series for Cannon's 3-pin circular connectors - invented by them - now an industry generic term. [Ray A. Rayburn tells the whole story: "At one time Cannon made a large circular connector series that was popular for microphones called the P series (now known as the EP series). Mics used the 3-pin P3 version. Some loudspeakers use the P4 or P8 versions of this connector to this day (Neutrik Speakon NL4MPR 4-pole chassis mount and all Speakon 8-pole chassis mount connectors are made to fit the same mounting holes as the Cannon EP series). In an attempt to make a smaller connector for the microphone market, Cannon came out with the UA series. These were 'D' shaped instead of circular and were used on such mics as the Electro-Voice 666 and 654. There was a desire for a smaller yet connector. Someone pointed out the small circular Cannon X series. The problem with this was it had no latch. Cannon rearranged the pins and added a latch, and the XL (X series with Latch) was born. This is the connector others have copied. Later Cannon modified the female end only to put the contacts in a resilient rubber compound. They called this new version the XLR series. No other company has copied this feature."] 2. The standard connector for digital and analog balanced line interconnect between audio equipment.
consonant Speech. 1. (noun) A speech sound in which an articulatory gesture stops or modifies the flow of the voiced sounds (vowels). Examples are "b", "k", and "n". 2 (adjective) Smooth and harmonious. The opposite of dissonant. [Bregman]
constant directivity (CD) horn (also known as uniform coverage or constant coverage horns) A horn-loaded high frequency driver that exhibits more or less constant distribution (or directivity) of high-frequency sound in the horizontal direction (and vertical, but horizontal is considered more important). The ideal is a broadband directional loudspeaker producing a beam pattern essentially constant for all frequencies above a certain cutoff frequency (i.e., the crossover point) over a 90, 60 or 40 degree horizontal arc depending upon design (termed long-, medium- and short-throw respectively), and around 40 degree vertical spread. This is done by using one of several special dual shaped horn designs created to solve the traditional problem of horn-loaded driver output varying with frequency. All CD horns exhibit a high frequency roll-off of approximately 6 dB/octave beginning somewhere in the 2 kHz to 4 kHz area. Fixed EQ boost networks that compensate for this are known as CD horn EQ circuits. Well designed CD horns can produce uniform coverage over a wide frequency range of 600 Hz to 16 kHz.
constant group delay See group delay.
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 interchangeable. The bandwidth remains constant for all boost/cut levels. For constant-Q designs, the skirts vary directly proportional to boost/cut amounts. Small boost/cut levels produce narrow skirts and large boost/cut levels produce wide skirts. See the RaneNote Constant-Q Graphic Equalizers, the RaneNote Operator Adjustable Equalizers, and the RaneNote Signal Processing Fundamentals Compare with proportional-Q and true response equalizers.
constant splay array See line arrays.
constant-voltage The common name given to the general practices begun in the 1920s and 1930s (becoming a U.S. standard in 1949) governing the interface between power amplifiers and loudspeakers used in distributed sound systems. Installations employing ceiling-mounted loudspeakers, such as offices, factories and schools are examples of distributed sound systems. The standard was derived from the need to minimize cost and to simplify the design of complex audio systems. One way to minimize cost is to minimize the use of copper, and one way to do that is to devise a scheme that allows the use of smaller gauge wire than normal 8 ohm loudspeakers require. Borrowing from the cross-country power distribution practices of the electric companies, this was done by using a transformer to step-up the amplifier's output voltage (with a corresponding decrease in output current); use this higher voltage to drive the (now smaller gauge due to smaller current) long lines to the loudspeakers; and then use another transformer to step-down the voltage at each loudspeaker. Clever. This scheme became known as the constant-voltage distribution method. The term "constant-voltage" is quite misleading and causes much confusion until understood. Point 1: In electronics, two terms exist to describe two very different power sources: "constant-current" and "constant-voltage." Constant-current is a power source that supplies a fixed amount of current regardless of the load, so the output voltage varies, but the current remains constant. Constant-voltage is just the opposite. The voltage stays constant regardless of the load, so the output current varies but not the voltage. Applied to distributed sound systems, the term is used to describe the action of the system at full power only. This is the key point in understanding. At full power the voltage on the system will not vary as a function of the number of loudspeakers driven, that is, you may add or remove (subject to the maximum power limits) any number of loudspeakers and the voltage will remain the same, i.e., constant. Point 2: The other thing that is "constant" is the amplifier's output voltage at rated power -- and it is the same voltage for all power ratings. Several voltages are used, but the most common in the U.S. is 70.7 volts rms. The standard specifies that all power amplifiers put out 70.7 volts at their rated power. So, whether it is a 100 watt, or 500 watt or 10 watt power amplifier, the maximum output voltage of each must be the same (constant) value of 70.7 volts. This particular number came about from the second way this standard reduced costs: Back in the late '40s, UL safety code specified that all voltages above 100 volts peak created a "shock hazard," and subsequently must be placed in conduit. Expensive. Bad. So, working backward from a maximum of 100 volts peak (conduit not required), you get a maximum rms value of 70.7 volts (Vrms = 0.707 Vpeak). [Often "70.7 volts" is shortened to just "70 volts." It's sloppy; it's wrong; but it's common -- accept it.] In Europe, the most common level is 100 volts rms (although 50 V and 70.7 V are used too). This allows use of even smaller wire. Some large U.S. installations used as high as 210 volts rms, with wire runs of over one mile! Remember, the higher the voltage the lower the current, and consequently the smaller the cable and the longer the line can be driven without significant line loss. [The reduction in current exceeds the increase in impedance caused by the smaller wire because of the current-squared nature of power.] In some parts of the U.S., safety regulations regarding conduit use became stricter, forcing distributed systems to adopt a 25 volt rms standard. This still saves conduit, but adds a considerable increase in copper cost, so its use is restricted to small installations. Modern constant-voltage amplifiers either integrate the step-up transformer into the same chassis, or employ a high voltage design to directly drive the line without the need for the transformer. Similarly, constant-voltage loudspeakers have the step-down transformers built-in. Both 70.7 volt amplifiers and loudspeakers need only be rated in watts. An amplifier is rated for so many watts output at 70.7 volts, and a loudspeaker is rated for so many watts input (to give a certain SPL). Designing a system becomes a relatively simple matter of selecting speakers requiring so many watts to achieve the target SPL (quieter zones use lower wattage speakers, etc.), and then adding up the total to obtain the amplifier(s) power. For example, say you need (10) 25 watt, (5) 50 watt and (15) 10 watt loudspeakers, then you need at least 650 watts of amplifier power (actually you need about 1.5 times this due to real world losses, but that's another story). [See the RaneNote Constant-Voltage Audio Distribution Systems for more details]
[Clarifying comment from SynAudCon’s Pat Brown: “The voltage is only 70.7 Vrms for the sine wave used to rate the amplifier, transformers, etc. The actual voltage is a program audio waveform and can be any voltage. It's common for designers to max out the taps on the loudspeakers and then throttle the amp back from full output. If they do that, it's still a constant voltage system, but operating at a lower voltage. It's better to think of it as a "100 Vpeak" distribution system, with 100 V being 0 dBFS. That puts a max constraint on the waveform, but the audio signal can be any crest factor and therefore any rms voltage. The peaks don't have to hit 100 V, that's just the limit.”
Further comment: "The system is constant voltage because the voltage on the line is independent of the load impedance. This is why it is important to not overload the amplifier (too many loudspeakers) because this would cause the voltage to drop. The "rated voltage" of the line (e.g., 70.7 Vrms) is for a sine wave reference tone. It has nothing to do with the actual audio program signal that will be played over the system. As such, one is never likely to measure "70.7 Vrms" on a ""70 V system," unless they hook-up a tone generator and drive the amplifier to clipping."]
contact microphone A musical instrument pickup designed to respond to direct (i.e., in contact) vibrations, such as those found on a violin or cello. One example is the FRAP.
content-based identification See: CBID.
contour control DJ mixers. A control found on professional DJ performance mixers used to change the shape or taper (contour) of the fader action. Thus at, say, 50 % of travel, a fader may allow 50 %, or 10 %, or 90% of the audio signal to pass depending on the taper of the control. The contour control (switched, continuous or stepped variable) changes this amount.
control voltage In audio electronic circuits using voltage-controlled amplifiers, or other gain-controllable devices, a DC voltage proportional to the audio input signal amplitude, sometimes frequency dependent, used to set the instantaneous gain of a VCA or other device. It is normally developed in the side-chain of the electronic circuit.
convolution A mathematical operation producing a function from a certain kind of summation or integral of two other functions. In the time domain, one function may be the input signal, and the other the impulse response. The convolution than yields the result of applying that input to a system with the given impulse response. In DSP, the convolution of a signal with FIR filter coefficients results in the filtering of that signal.
convoler Electronics. A three-port device whose output signal is the convolution of two time waveforms applied simultaneously to the input ports; convolution is achieved by physically passing the input signals over one another at the output transducer. [IEEE]
Cook, Emory (1913-2002) American engineer and audio pioneer best known for his many contributions to vinyl disc technology including the left-right binaural disc. He produced the first audiophile record in 1949 and demonstrated it at the Audio Fair in New York, subsequently founding the company Sounds of Our Times, the first high fidelity record company. He was a founding member of the AES. Said to be the first to record the sound of rain so accurate that it sounded "wet."
cooker wire A British term for the large gauge solid wire (i.e., not stranded) used for electric cookers. Popularly used in ABX testing to confound and expose the aural hallucinations of those obsessed by exotic loudspeaker wire.
cool jazz Variation of bebop; referring mostly to West Coast jazz performed mainly by white musicians.
copyright The legal right granted to an author, composer, playwright, publisher, or distributor to exclusive publication, production, sale, or distribution of a literary, musical, dramatic, or artistic work. [AHD] For an enlightening editorial, see: Joe Bob's (aka John Bloom) write-up titled "Wrong copyright laws."
Corba (common object request broker architecture) An ORB (object request broker) standard developed by the OMG (object management group). Corba provides for standard object-oriented interfaces between ORBs, as well as to external applications and application platforms (from Newton's Telecom Dictionary). Not to be confused with CobraNet.
core Microprocessors. Shortened form for multicore.
Coriolis effect Physics. A pseudo force used mathematically to describe motion, as of aircraft or cloud formations, relative to a noninertial, uniformly rotating frame of reference such as the earth. [AHD] The Coriolis effect is the basis of micromachine gyroscopes.
corner frequency Same as -3 dB point, or the 3 dB down point; see passband.
correlation A mathematical operation that indicates the degree to which two signals are alike.
corrido Music. A Mexican ballad or folksong. [AHD]
Costello, Elvis Stage name of Declan MacManus.
coulomb Abbr. C The meter-kilogram-second unit of electrical charge equal to the quantity of charge transferred in one second by a steady current of one ampere. [After Coulomb, Charles Augustin de.] [AHD]
counterpoint Music. 1. Melodic material that is added above or below an existing melody. 2. The technique of combining two or more melodic lines in such a way that they establish a harmonic relationship while retaining their linear individuality. 3. A composition or piece that incorporates or consists of contrapuntal writing. [AHD]
Countryman, Carl (19??-2006) American engineer, inventor and entrepreneur founder of Countryman Associates, Inc., whose professional headsets are considered the smallest and lightest available.
coupling or mutual coupling Loudspeakers. General term describing the combining behavior of two or more drivers reproducing the same frequency. If two or more identical loudspeakers are mounted such that their acoustic centers are close together (i.e., some fraction of a wavelength), their acoustic outputs over some frequency range will combine (couple) and propagate forward as one waveform, thus two smaller drivers behave as one big driver. [This is the simple vague answer, a detailed specific answer requires a great deal more.]
Mark Gander, VP of pro marketing for JBL, puts it this way: "The correct maximum distance that mutual coupling occurs depends on what you want to define as the limit of coupling. For example, is it the maximum approaching +3 dB, or when it reverts to unity gain? It's a gradual transition, so either 1/4 wavelength or 1/2 wavelength separation distance is just a rule of thumb." [Gander sites Lee Henney's Radio Engineering Handbook, 5th ed., Ch. 11 'Loudspeakers and Room Acoustics,' as a useful source that shows the response from groups of pistons at various distances, following the work of Klapman (Klapman, S. J., "Interaction Impedance of a System of Circular Pistons," J. Acoust. Soc. Am., vol. 11, p. 289, 1940.)"
John Murray, Digital Audio Lab Manager, Columbia College Chicago, explains: "Mutual coupling is when multiple drivers produce relatively more output at the low end of their response curve than a single driver. This occurs when the drivers are close enough together to have less than 90 degrees of path length difference for the wavelengths of interest at a given listening position. This phenomena is position-dependant, and is, in fact, what causes the high level portion of lobing. At shorter wavelengths (higher frequencies) and listening positions farther off-axis of the drivers, the phase difference becomes destructive which results in the nulls of lobing. Even with drivers that are touching, mutual coupling over a wide listening area are virtually always below 300-500 Hz.
Chuck McGregor, Technical Services Manager for EAW, says, "It depends." And goes on to explain: "There is no such thing as a correct, maximum source spacing distance for mutual coupling. First one has to define what they consider as mutual coupling (i.e., at what level off-axis does one stop considering the sources as no longer being mutually coupled) and then what is the criteria is for a particular situation, meaning the frequency to which one requires the coupling and the overall angle over which it is needed. Based on this stuff you can figure out the maximum, acceptable driver spacing.
Harry Olson analyzes this (although he does not call it mutual coupling) as a double or doublet source in his book, Acoustical Engineering, section 2.3.
McGregor's personal view: "First, mutual coupling will occur on-axis even if the center-to-center distance of two sources is 100 light years. At 1/2 wavelength separation they cancel completely at 90 degrees off-axis. At 45 degrees off-axis the signal is roughly 6 dB down, i.e. the equivalent of one source. Does this mean their mutual coupling beamwidth is limited to 45 degrees or is it limited at the 6 dB down point? Maybe it is 3 dB down over a lesser angle?"
McGregor offers this as a detailed definition: "Mutual coupling is when the outputs of two or more acoustical sources producing the same signal combine (couple) and propagate forward as one waveform. In this way, two smaller drivers can behave as one larger driver. While any number of sources can mutually couple, for clarity this discussion will focus on two sources.
The amount of coupling directly on axis between two sources producing the same signal will result in a 6 dB increase in level. On-axis, the spacing of these sources has absolutely no effect on this result. However, because the two sources must be physically separated, the coupling decreases off axis as the path lengths from each source to the listener increasingly differ. This is because the two waveforms become increasingly out of phase. For a given source spacing, the higher the frequency is, the more quickly off-axis this occurs. Likewise for a given wavelength (frequency) the wider the source spacing, the more quickly off-axis this occurs. Thus, the amount of mutual coupling at any point off-axis depends on both the source spacing and the wavelength (frequency) of the sound being produced.
What is considered mutual coupling? The broadest definition is that any multiple sources producing the same signal whose outputs acoustically combine to produce an increase in level over that of one of the sources means mutual coupling is taking place.
For audio purposes, changes of 3 dB and 6 dB are often used as typical criteria for acceptable increases or reductions in level. For two sources, a 3 dB decrease from the on-axis coupling of 6 dB occurs when the path length difference from the sources to the listener is 1/4 wavelength. This equals a 90 degree phase shift between the two waveforms. Likewise for two sources, a 6 dB decrease from the on-axis coupling of 6 dB occurs when the path length difference from the sources to the listener is 1/3 of a wavelength. This equals a 120 degree phase shift between the two waveforms. It also results in a level that equals the output of one source, meaning the amount of mutual coupling is effectively equal to zero.
Thus, the best definition for mutual coupling is defined by what is acceptable for any given situation. This can vary from the full, on-axis mutual coupling to the effective absence of mutual coupling, which is where the level decreases to be equal to or less than of one of the sources. Contrary to popular notions, there is no particular driver spacing that results in mutual coupling. Mutual coupling is defined by the level below which mutual coupling is not longer considered mutual coupling. This is an arbitrary level but, in any case, it cannot be below the level of one of the sources. The source spacing and the wavelength (frequency) of the signal then determines the angle over which the combined wavefront falls within the chosen definition of being mutually coupled."
cover buzz "The sensation felt when hearing a cover version of a song one already knows." [A Dictionary of the Near Future by Douglas Coupland, NY Times, September 12, 2010.]
CPA (covert peak area) Hearing Localization. "... defined as the spatial constellation of loudspeakers that generates maximal sound pressure at the entrance of the ear canal for specific bands of frequency. " [Rogers & Butler, The linkage between stimulus frequency and covert peak areas as it relates to monaural localization]
CPC (circuit protective conductor) Chiefly British abbreviation meaning earth ground, or technically a system of conductors joining together all exposed conductive parts and connecting them to the main earthing terminal.
cps (cycles per second) Old term for Hz.
crap (completely ridiculous audio performance) Favorite acronym used to describe the characteristics of poor sound equipment. (Thanks C.D.!)
crate Music. DJ jargon for record box.
crate diggin' or diggin' in the crates Music. DJ slang for finding records for their collection (dig for records to play at clubs, or searching for sounds to create new music), or into their record box to find that exactly right record for the moment.
CRC (cyclic redundancy check) An integrity checking process for block data. A CRC character is generated at the transmission end. Its value depends on the hexadecimal value of the number of ones in the data block. The transmitting device calculates the value and appends it to the data block. The receiving end makes a similar calculation and compares its results with the added character. If there is a difference, the recipient requests retransmission.
Creamfields A world-class HUGE dance festival held yearly in Daresbury, England. Also held in various international venues.
creepage distance Shortest path along the surface of insulating material between two conductive parts.
crest factor The term used to represent the ratio of the peak (crest) value to the rms value of a waveform measured over a specified time interval. For example, a sine wave has a crest factor of 1.4 (or 3 dB), since the peak value equals 1.414 times the rms value. Music has a wide crest factor range of 4-10 (or 12-20 dB). This means that music peaks occur 12-20 dB higher than the rms value, which is why headroom is so important in audio design.
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.
critical distance Acoustics.The distance between source and listener where the direct sound level equals the reverberant sound level. Good article found here: "Critical Distance and Direct Sound Field," by Peter Mapp, Sound and Communication, April 2009, p. 16.
cross-coupled A type of balanced line driver loosely based on servo-loop technology. Developed to emulate some of the features of a balanced line output transformer, the circuit employs positive feedback taken from each side of the outputs coupled back (cross-coupled) to the opposite input circuitry where it is used to fix the gain of the positive and negative line drivers. Each gain is typically set to unity (one) for normal operation and changes to two whenever either of the output lines is shorted to zero. In this manner, it emulates a transformer in that there is no change in output level if one of the lines becomes short-circuited to ground; however, since the gain of the ungrounded side has increased 6 dB then the headroom of the system has been reduced by 6 dB due to the short. In this sense this circuit does not act like a transformer, which does not change gain when one side is shorted to ground. See the RaneNote Unity Gain and Impedance Matching: Strange Bedfellows. [Historical Note: Peter Clark of Harrison Consoles writes that back in late 1978 or early 1979: "The 'MCI' cross-coupled balanced line driver was brought to them by the then German dealer, Rudiger Bart, who brought this circuit and its inventor, Peter Leunig, who wanted to sell it to MCI. MCI said 'That's very nice, but 'No thanks,' then went on to use it anyway!]
crossfade or crossfader Within the pro audio industry, a term most often associated with DJ mixers and broadcast. 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). It is the crossfader that becomes the main remix tool for turntablists. The exact origin of the first use of a crossfader in the DJ world has proven difficult to track down. It seems certain to have come out of the broadcast industry, where the term "fader" has been in use since at least the '50s (mentioned throughout the Radiotron Designer's Handbook, 4th ed., 1952) and the term "cross-fading" shows up in the Tremaine's Audio Cyclopedia in 1973. Richard Wadman, one of the founders of the British company Citronic designed the earliest example documented so far. It was called the model SMP101, made about 1977, and had a crossfader that doubled as a L/R balance control or a crossfade between two inputs. [Anyone who can document an earlier example of a DJ crossfader please write me.] For a history of DJ-use crossfader circuitry see Evolution of the DJ Mixer Crossfader by Rane's ace DJ mixer designer, Rick Jeffs, for additional details. Contrast with pan, balance and fader controls.
cross-framing A term borrowed from the construction industry (meaning diagonal bracing) by TimeLine Vista, Inc. (now defunct) the original developer and manufacturer of the TASCAM-branded MX-2424 (24-track, 24-bit hard disk recorder) to describe their sync product with "independent cross-framing" capability that allows a longitudinal timecode (LTC) reader and two generators to be set to different frame rates.
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. Since audio wavelengths vary from over 50 feet at the low frequency end, to less than one inch at the high frequency end, no single loudspeaker driver can reproduce the entire audio range. Therefore, at least two drivers are required, and more often three or more are used for optimum audio reproduction. 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 - "woof, woof" = low frequencies) works to reproduce everything below 800 Hz, while both drivers work reproducing the region immediately around 800 Hz (the crossover region), and finally, only the last driver (the tweeter - "tweet, tweet" = high frequencies) 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, or sometimes dB/decade [useful rule-of-thumb: 6 dB/octave approximately equals 20 dB/decade]. See the RaneNote Signal Processing Fundamentals.
crossover cable See: Ethernet crossover cable
crossover distortion Amplifiers. Term for the distortion products found in class AB amplifiers created by the dead zone between the upper and lower output devices where neither device is fully operating.
crosspoint Audio Signal Processing. Found in matrix-mixers, referring to a device, usually a switch, potentiometer, VCA or DAC, located where two schematic or block diagram lines intersect or cross. Typically this is drawn with the inputs entering from the left and exiting to the top depending upon the setting of the crosspoint device. For example if Input 4 is to exit Output 6 then at the intersection of Input 4's signal path and Output 6's exit path there will be a switch that is closed, or a potentiometer set for something other than off, or a VCA or DAC that is at least partially turned up. Crosspoints form the heart of a router.
crosstalk (recording) See print-through.
crosstalk (signal) 1. Undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another. 2. 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. Note: In telecommunications, crosstalk is usually distinguishable as speech or signaling tones. See the RaneNote Audio Specifications.
crotchet See: quarter-note.
crump 1. To crush or crunch with the teeth. 2. To strike heavily with a crunching sound. 3. To make a crunching sound, especially in walking over snow. 4.The sound of an exploding shell. [AHD]
crunk 1. The harsh cry of a bird; a croak. Giving rise to variations of crunkle meaning wrinkle, rumple, crinkle or to make a harsh dry sound as by grinding the jaws, etc. [OED] 2. Music. A style of Southern rap music. Hit the link for more details. See: krunk.
Cry Baby See: wah-wah pedal
crystal See: piezo.
cubit An ancient unit of linear measure, originally equal to the length of the forearm from the tip of the middle finger to the elbow, or about 17 to 22 inches (43 to 56 centimeters). [AHD]
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. Music. a. A section of music used in film or video ranging from a short piece of background music to a complex score. b. An extract from the music for another part printed, usually in smaller notes, within a performer's part as a signal to enter after a long rest. c. 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. [AHD]
cumbia Music. Popular Latin American music genre.
cumulative spectral decay See: waterfall display.
Curie, Marie Originally Manja Sklodowska. (1867-1934). Polish-born French chemist. She shared a 1903 Nobel Prize with her husband, Pierre Curie (1859-1906), and Henri Becquerel for fundamental research on radioactivity. In 1911 she won a second Nobel Prize for her discovery and study of radium and polonium.
Curie temperature The temperature at which magnetic materials demagnetize. Specifically a transition temperature marking a change in the magnetic or ferroelectric properties of a substance, especially the change from ferromagnetism to paramagnetism. Also called Curie point. [After Pierre Curie.] [AHD]
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. [AHD] [As electrons flow in one direction, the spaces left behind, called holes, appear to flow in the opposite direction. Thus, current can be visualized as electron flow (negative current flow), or in the opposite direction, hole flow (positive current flow, sometimes called conventional current flow).]
current density Symbol J, Electromagnetism. The electric current per unit area of cross section.
current intermittor Antiquated name for a snap-action switch.
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.
cycles per second Abbr. cps Old term for Hz.
cymatics The science of visualizing audio frequencies.
cymbal Musical Instrument. A percussion instrument consisting of a concave brass plate that makes a loud clashing tone when hit with a drumstick or when used in pairs. [AHD]
CWLE (clockwise lead end) Refers to electric motor rotation viewed from the end where the hook-up wires exit.