Sound Glossary

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A-B microphone pair - Also: "A-B Stereo," "Time Difference Stereo." A stereo micing technique that uses two spaced omnidirectional microphones. The spacing of the microphones provides small differences in time information; the human ear senses these differences and translates them into localization and imaging data. Generally used for recording.

A-B System - A sound reinforcement design scheme developed and pioneered by sound designer Martin Levan in the late 1970s. In order to provide for a natural, balanced sound, where close proximity between open wireless microphones would not affect the reinforced sound (when two open mics are placed close together, the sound source will reach one microphone before the other; the sum of these two audio signals will cause audible phase distortion, making for a usually "tinny" sound), Levan designed a sound reinforcement system comprised of, essentially, two separate reinforcement systems. If one open mic was routed to one system, and the other to the other system, completely independent of each other except at the control level (i.e. mixing desk), electronic phase cancellation between the two microphones would not occur. Other sound designers eschew this scheme, preferring to have a single system divided into orchestra and vocal systems. Phasing between microphones is alleviated by an operator with quick reflexes, or the application of equalization at certain points of the show. Yet other designers prefer to use a scheme dubbed "A-B-C System," in which two systems are used for vocals, and one system for orchestra. The main drawback to A-B and A-B-C systems is the cost of doubling or even sometimes tripling the number of loudspeakers and associated processing equipment.

A/D converter - Also: "AD Converter;" short for "Analog-Digital Converter." An electronic device which converts an analog audio signal in its electrical form into a digital binary data stream which can be stored, edited, manipulated, and later converted back to an analog audio signal. Most digital recording equipment and digital processing equipment have such converters built in, although standalone units are available. See Digital Audio text for a complete explanation of exactly how they convert the signal.

Absolute Phase - Absolute Phase is a state of audio nirvana in which all equipment and interconnects between a microphone and a loudspeaker maintain correct polarity, such that a positive force to a microphone will ultimately produce a positive force from a loudspeaker. When two pieces of equipment are interconnected correctly, it can be said that they are in phase.It should be noted, however, that we are actually observing correct polarity; polarity changes phase in increments of pi radians, or 180 degrees.

Absolute Time Code - Abbr: "ABS", "ATC." Absolute Time Code is a digital code recorded into the subcode area of a digital tape format that tells the machine at what point the tape is. It can be used to synchronize the tape to other equipment or can be converted to dictate SMPTE time code. Absolute Time Code begins at "0h 00m 00s 00f" at the start of recording, and increments from there.

Absorption - In acoustics, to absorb is to receive a sound wave without echo or reflection. Thus, the absorption of sound is the phenomenon by which acoustical energy is lessened by passing through a medium. The resultant effect is little, or less, reflection and reverberation. The ability of a medium to absorb sound is quantified by the absorption coefficient, a number between 0 (no absorption) and 1 (complete absorption). The absorption coefficient is dependent upon the frequency of the sound wave and the angle at which the sound wave strikes the surface (called the angle of incidence.)
AC-1 - AC-1 is a type of digital audio coding scheme, developed by Dolby Laboratories in 1984, to minimize the bandwidth necessary for digital audio transmission. It is a rather simple decoder but a relatively complex encoder system. It is still in use in satellite and cable delivery systems.
AC-2 - AC-2 is another digital coding scheme developed by Dolby Labs. It operates on the principle that the human ear masks certain frequencies, if other, louder frequencies are present. The audio quality remains high while the bit rate is low. Used in satellite and terrestrial links and digital audio storage systems.
AC-3 - AC-3 is yet another digital audio coding scheme commonly referred to as "Dolby Digital." Similar to AC-2, it uses a psychoacoustic scheme to remove masked frequencies, thus it requires less storage space or transmission bandwidth. It can support up to five full-range channels and a separate bass-only effects channel (thus the term "5.1"). It is more flexible than AC-2 and has features enabling it to be played back on mono, stereo, Dolby Pro Logic systems, and full 5.1 systems. It is now commonly used on current laser discs and DVD discs, and will be the standard audio delivery system on the United States' HDTV (high definition television) system.
Acoustic Suspension - A type of speaker design using a sealed cabinet. Primarily used for low frequency enclosures, acoustic suspension designs use the air mass within the cabinet and behind the driver as a "spring" to help return the relatively massive speaker to the rest position. This allows heavier, longer throw drivers to be used, but results in a less efficient design requiring more amplifier power. Compare with "Bass Reflex."
Acoustics - 1] The study of sound-wave motion and sound behavior both within an enclosure and out of doors.2] The qualities of a room with respect to transmission of sound.

Active Crossover - A loudspeaker system component, usually a standalone unit, which divides an audio signal into two or more frequency bands, usually "low," "mid," and "high." Most standalone units will permit the user to set the crossover point(s) manually. Compare with Passive Crossover. See Crossover for more information.

AES - The Audio Engineering Society is a professional society of those involved in audio who work to set standards for the audio community. The AES provides for technological innovations and communication within the audio industry.

AES/EBU Interface - A transmission protocol standardized by the Audio Engineering Society and European Broadcast Union dictating the transfer of professional two-channel digital audio signals (AES3-1992). Transmission is achieved via a single twisted-pair cable with shield, terminating in 3-pin XLR-type connectors over 75-ohm cable.
Aesthetic - Often applied to theatrical designs or directing styles; in sound, the end product of the sound system and how it evokes mood or enhances the play.

After-Fade Listen, or AFL - Abbr: "AFL." Refers to a monitor signal on a mixing desk taken after the main input or output fader; thus the fader position affects the level heard in the AFL monitor. Some mixing desks take the AFL signal post-pan, so that the engineer can hear the signal as it is in the stereo field. Different manufacturers will use different nomenclature in regards to their monitoring systems, so be careful.Compare with PFL and Solo.

Aliasing - In the digital domain, aliasing is a type of distortion when the analog frequency being sampled is higher than one-half the sample rate (i.e. when a frequency of 30,000 Hz is sampled at one-half of 44,100 Hz (22,050 Hz). One-half the sample rate is called the "Nyquist Frequency." When a frequency to be sampled exceeds the Nyquist Frequency, it is "folded over" and becomes an audible component of the signal. Most digital audio converters have filter sections to prevent aliasing from occurring.

Alternating Current - Abbr: "AC." Electrical current that periodically alternates its phase with relation to time. Standard household electricity works in this fashion. In the United States and Japan, the current changes direction at 60 Hz (sixty times per second), whilst in most of the rest of the world, the current changes direction at 50 Hz. Audio signals are, technically, alternating current, with the frequency of alternation corresponding to the frequencies of the sound present. Compare with "Direct Current (DC)".[Alternating Current was chosen as the preferred household electrical distribution system because of its ability to travel long distances with relatively less loss; George Westinghouse pioneered this design while Thomas Edison futilely pushed for Direct Current distribution.]
Ambience - The characteristic sound of a location that tells the ear it is listening in a particular room, concert hall, influenced by reflections, reverberation, and such.
Ambient Noise - The prevailing sound field in a room in the absence of an applied signal from a loudspeaker, musical instrument, or other sound source.
Ambisonics - A surround-sound system designed to reproduce a full three-dimensional sound field. It was not a simple system, but it was capable of giving the listener a full, 360-degree sound field. Special microphone arrays and signal processing are required to reproduce and playback Ambisonics-encoded signals.
American Wire Gauge (AWG) - A system in the United States for measuring thickness of wire. The lower the number, the larger the diameter of the wire. Common "Zip Cord," for household lamps, is 16AWG; common telephone wire is 22AWG, etc., etc. Every other country that cares about wire size uses a metric equivalent- (mm^2).

Amperage - Abbr: "A"; measured in "Amperes," "Amps, "A." Represented in electrical equations by "I". Named after AndrŽ Marie Ampre, it is defined as the steady current that, when flowing in straight parallel wires of infinite length and negligible cross-section, separated by one meter in free space, produces an electrical force between the wires of 2 x10^-7 Newtons/meter.In English, it is the number of electrons in a conductor flowing past a particular point in a given amount of time. See "Basic Electricity Principles" for more information.

Amplifier - A device in which a small amount of input power controls a larger amount of output power. Used in electrical circuits to convert a small electrical signal into a large electrical signal. Used in sound systems in a myriad of locations-- converting mic-level signals to line-level, line-level to loudspeaker levels, etc., etc.
Amplifier Class - Audio power amplifiers are subdivided into classifications that demarcate differences in design, usually in the output stage.
Amplifier Class A - An amplifier design in which the output stage devices (usually an output stage for the negative side of the signal, and an output stage for the positive side of the signal) are passing current at all times, even when the input stage is idle. Since the output stages are "active" at all times, presence of an input signal causes output current to be diverted directly to the loudspeakers-- the slew rate is very quick-- there is only a very small delay between the introduction of signal at the amplifier's inputs and the appearance of signal at the amplifier's outputs. If all stages of the amplifier are biased in Class A mode, and the amplifier produces absolutely all the current at its output, regardless of input signal, it is called a "Pure Class A" amplifier. Because of the full-bias-current-on state of Class A amplifiers, they are the most inefficient of all designs; however, Class A amplifiers are the most linear.
Amplifier Class AB - An amplifier design which is basically a combination of Class A and Class B operation. An amplifier is said to be in Class AB operation if the amplifier operates in Class A for part of its output, and turns on additional current for the rest of its output. The amplifier's slew rate is slower in Class AB operation than in Class A, because there is a measurable length of time between the appearance of input signal and the appearance of output signal. The Class AB amplifier type is the most popular due to its increased efficiency and excellent linearity.
Amplifier Class B - An amplifier design which is essentially the opposite of Class A operation. No current flows when the output devices are idle, and thus must turn on from a zero-current state when signal is present. In addition, both output devices (negative and positive) are never active at the same time. If given a sine wave, each output device will operate for half the waveform. Thus, the Class B operation is very efficient; however, the linearity of the amplifier suffers when the signal approaches the point at which the output devices change; Class B operation amplifiers are generally not used for professional audio equipment, and is reserved for low-power operations such as radios.
Amplifier Class C - An amplifier design which is used for radio-frequency transmission. Similar to Class B operation, each output stage device (negative, positive), is turned on for less than one-half cycle, and pulsed on and off through the duration of the half-cycle. A Class C amplifier can produce great amounts of output power; although the distortion is great, RF circuitry has been developed and tuned to alleviate the effects of this distortion.
Amplifier Class D - An amplifier design which is also switched. The output devices are switched on and off at least twice per cycle. In theory, because the output devices (negative and positive) are completely on or completely off, no power is dissipated, so theoretically Class D operation is 100% efficient. Real-life Class D amplifiers are, of course, not 100% efficient, but approach 90%.
Amplifier Class E - An amplifier design designed specifically for rectangular input pulses, not audio waveforms. The output stage produces a waveform similar to a damped square pulse.
Amplifier Class G - An amplifier design utilising, essentially, dual Class AB output stages which use two different power supplies; the input signals determines which power supply is used. Highly efficient, and becoming popular.
Amplifier Class H - An amplifier design using the Class G design and modulates the second, higher power supply voltage with the input signal. This design allows only the necessary amount of voltage to be used to operate the amplifier.
Amplitude - In physics, amplitude is the maximum value of a periodically varying quantity. This definition can be applied to electronics: the maximum absolute value reached by a voltage or current waveform. In mathematics: the maximum absolute value of a periodic curve measured along its vertical axis.In sound, amplitude is the strength of a signal or sound without regard to its frequency content. In audio signals, the amplitude is generally the signal voltage, but this quantity does is not necessarily an analog to the real world, where sound level is measured in dB SPL (decibels of Sound Pressure Level) at a given point in time.
Analog - An analog is a representation of something. In sound, analog representations of sound reproduce the exact waveform, transferring it through different mediums. For example: changes in sound pressure are represented by changes in voltage-- the microphone creates an electrical analog of the physical sound waves. It is important to note that the analog signals in a sound system are continuous- a continuous electrical signal will produce a continuous physical analog when driving a loudspeaker. Compare with Digital, which takes samples, small chunks of a continuous waveform, and calculates its data based on that given moment of time before moving on to the next chunk of the waveform.
Anechoic - Literally, echo-free. Anechoic refers to the absence of sound wave reflections. It is nearly impossible to create such a situation; the outdoors is very close, but there are still reflections from the ground, field-hockey players, etc. There are institutions and corporations who have anechoic chambers, rooms coated in sound-absorbing material, which come very close to being fully anechoic. These rooms are usually used for testing, measuring, and developing microphones and loudspeakers. It can also prove to be a good room for solitary confinement; due to the complete lack of reflections and echoes, people have been known to go insane after hearing their own blood rush around their head for a few hours.
Anti-aliasing Filter - A low-pass filter used at the input of digital audio converters to attenuate frequencies above the half-sampling frequency (the "Nyquist Frequency") to prevent aliasing.

Apparent Power - Physically, the result of multiplying the RMS voltage by the RMS current in an electronic circuit. It is expressed in watts (W) for resistive loads and in voltamperes (VA) for reactive loads. It is the amount of power that the casual observer thinks is available, but because of the power factor may not be-- the real power is usually less.

Area-micing - In contrast to close-micing, area micing is the general pickup of a playing area, such as a stage, with directional microphones such as rifle (shotgun) or foot (floor) microphones.
Array - Refers to a collection of two or more loudspeakers, rigged side-by-side or top-to-bottom or both. While the word "Cluster" is often used interchangeably, an array is generally location-independent. A loudspeaker array can be found stage left, stage right, or centrally hung in the center. A "cluster" generally refers to a centrally hung loudspeaker array.
Atmospheric Pressure - Pressure caused by the weight of the atmosphere. At sea level it has a mean value of one atmosphere but reduces with increasing altitude.
Attack - In musical and sound terms, "attack" is the beginning of a sound. Attack time is the time it takes a sound to go from silence to its maximum level. When using any sort of nonlinear processing, i.e. compression, expansion, or reverberation, it is important to note how the attack time can affect the resultant sound.
Attack Time - When referring to a compressor or expander, the attack time is designated as the time during which the output level moves from its pre-threshold level to the gain dictated by the compression or expansion ratio. In English: how fast a compressor or expander reacts.

Attenuate / Attenuator / Attenuator Pad - In electronics, to "attenuate" is to decrease the level of a signal. An "attenuator" is a device, usually a passive network, that accomplishes this task with negligible distortion, although in some cases attenuation is unintentional, such as the signal drop caused by using a long length of wire for transmission. In sound, attenuators are usually used to lower the level of an audio signal in a system to prevent overload and distortion. The network of resistors, inductors, and capacitors is also referred to as a "pad," or "attenuator pad." There are two basic types of pads, which differ in their network topology: L-pads and T-pads. A true L-pad network includes two variable potentiometers that are ganged together, which provides a constant input or output impedance regardless of attenuation. A volume control is a common example. While an L-pad network has two "legs" in its network, a T-pad network has three.Some microphones have a built in attenuator pad on the output stage of the microphone, reducing the output level by 10 or 20 dB, to prevent overloading the input stage of a mic preamplifier. Most mixing desks, too, have some sort of attenuator pad switch, reducing the level to the input stage of the channel by 15 or 20 dB.
Autoformer - Short for "Autotransformer," or "Self-transformer." An autotransformer is a transformer that does not have a true secondary coil-- there is just one winding with part of it acting as the primary, and the other acting as the secondary. Thus, there is no true isolation between the windings, and are eschewed in professional audio.

Automatic Gain Control - Abbr: "AGC". Automatic Gain Control circuits automatically adjust the level of incoming audio so it can be recorded or mixed properly. Essentially, they are semi-intelligent compressors often used in consumer recording equipment, alleviating the cost of knobs and pots.
Automatic Mic Mixer - A specialised microphone mixer designed to solve problems encountered in multiple-microphone systems such as those found in boardrooms, classrooms, courtrooms, and the like. It controls the live microphones by turning up microphones when someone is talking into them, and turning the off (or down) when they are not used. It is a voice-activated, real-time, semi-intelligent process. The unit considers the number of open microphones (important to prevent feedback), ambient room-noise (louder/softer overall program level), and quality (make quick changes without being noticed). Dan Dugan patented the first mixer and he is recognized as the father of the technology.
Automation - Usually refers to console automation-- technology that automates specific functions of a mixing desk. Some mixing desks can recall fader and input channel settings as "scenes" or "cues" and recall them at a later time. Newer technology provides for instant-recall of knob positions and control of other equipment.

Auxiliary - In mixing desks, the word "auxiliary" is used to describe a separate audio signal bus that provides a mix independent of the desk's main outputs or subgroups. The term "Auxiliary Send" or "Auxiliary Out" applies to the ancillary outputs of the desk, and the term "Auxiliary Return" or "Auxiliary In" applies to specific line-level inputs on a mixing desk. The two are designed to be used together, usually to send specific mixes to an effects processor, and return it to the desk. Auxiliary outputs can also be used to send a dedicated mix to different monitor systems.In most desks, each channel input will have several aux sends that can be used independently of each other.

Axis - When discussing microphone or loudspeaker polar patterns, the axis is the imaginary line drawn perpendicular to the front face of the microphone or loudspeaker diaphragm. Sounds arriving at the microphone at an angle to the axis or sounds emanating from a loudspeaker at an angle to the axis are said to be "off-axis". See also "Polar Patterns" and "Dispersion."


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Back-EMF, Back Electromotive Force - Describes the phenomenon found in all moving-coil electromagnetic systems, i.e. a speaker cone, whereupon, after the electrical audio signal stops, the speaker cone continues to move, creating a new voltage that tries to drive the output of the power amplifier. It does not sound good when loudspeakers do this, so amplifier manufacturers try to present a zero-ohm "dead short" to the loudspeaker. See Damping Factor.
Background Music - In industrial installations, often abbreviated "BGM." A distributed loudspeaker system, such as those found in malls and public-transportation terminals, designed to reproduce music at low levels to enhance the mood of the public. In theatre, appropriate music designed, composed, and utilised to enhance the mood of a play.
Baffle - A panel or surface whose sole purpose is to prevent the transmission of sound. Also "orchestra pit baffle" or "pit screen." Often comprised of many parts, common pit baffle designs incorporate a wooden frame with various types of sound-absorbing materials on the faces of the frame.In loudspeaker systems, a baffle is a panel or surface that reduces interference between sound radiated from the front and rear of the speaker driver by increasing the length from front to back.Also: to stupefy.
Baffled Stereo - A stereo micing technique, or set of stereo micing techniques, that utilise an acoustic baffle between the two microphones in a two-microphone stereo recording setup. The baffle has a positive effect in enhancing the channel separation... unless the baffle is fabricated from a reflective material-- baffles should be made from acoustically absorbent material to prevent reflections from the baffle influencing the recorded signal.
Balance Control - A potentiometer, most often found on consumer stereo preamplifiers and car audio equipment, used to adjust the loudness between left and right channels. A dual pot with an "M-N" taper form factor is used; an M-N taper describes a fader curve in which the first half of the fader (or potentiometer) curve is shorted-- full output, and then for the second half has a linear attenuator function. Two such pots, wired oppositely for each channel, comprise the balance control. At the center knob position, there is no attenuation of either channel. Rotating the knob away from the center position in either direction attenuates one channel while leaving the other untouched.

Balanced / Unbalanced - An audio wiring scheme referring to an electrical (audio) signal having two "legs" independent of ground. One leg is generally considered positive (+) with reference to ground, and the other negative (-). A third conductor, the shield, is an outer wrap of conductive metal encircling the two inner, signal-carrying conductors. In balanced wiring, when the signal reaches the destination, the negative copy of the audio signal is polarity-reversed and added to the positive signal. Any noise induced into the signal on its travels is also reversed; when combined with the non-reversed noise, the two noise signals cancel each other out. This phenomenon is called "Common Mode Rejection." Balanced lines are thus used for lengthy cable runs in which unbalanced wiring schemes would be susceptible to induced inteference. The shield functions as a true shield, sending any waste-material noise to ground.Unbalanced lines have only a positive (+) signal, and the negative signal is carried on the shield of the cable. Any noise induced into the cable will make its way into the audio signal.Another use of a balanced wiring scheme is coming into popularity: balanced power systems. The concept remains the same- instead of an AC scheme wherein there is a positive signal which carries 120V with respect to ground (US), a neutral which carries 0V with respect to ground (ideally), and a ground, the positive and neutral legs both carry inverted copies of 60V with respect to ground. In this case, again, the power supplies can cancel any noise induced into the AC line and produce cleaner audio. Theoretically.
Banana Plug - A Banana Plug is the name given to a connector originally designed by the General Radio Corporation that is occasionally found on loudspeaker cable and test leads for test equipment. Resembling a linear banana, the plug is designed to fit into the five-way binding posts found on the back of many an amplifier or loudspeaker cable. They are commonly found molded together in pairs (positive, negative) for amp-to-speaker connections. Its main advantage is that it can accept large-gauge wire and has a lot of connector surface-area, but unfortunately it is not lockable in most situations, nor is there any sort of strain relief on the cable-connector junction.
Band-limiting Filter - A low-pass and a high-pass filter in series, acting together to limit the overall bandwidth of a circuit system to a certain parameter of frequencies. Also band-pass filter. The low and high frequencies between which the filter allows signal to pass are usually determined by the filter's -3dB points.So-called because it limits a signal to a specific frequency range.
Band-pass Filter - A low-pass and a high-pass filter in series, acting together to limit the overall bandwidth of a circuit system to a certain parameter of frequencies. Also band-limiting filter. The low and high frequencies between which the filter allows signal to pass are usually determined by the filter's -3dB points.So-called because it limits a signal to a specific frequency range.

Bandwidth - Bandwidth is defined as a frequency span- the difference between a high frequency and a lower frequency.In sound, the word can be utilized in different ways, depending on context. As a simple example, an equalizer with cutoff frequencies (the filter's 3 dB point) of 200 Hz and 2000 Hz has a bandwidth of 1800 Hz. The audio bandwidth is generally defined as 20 Hz to 20,000 Hz, although there are harmonics that can extend far beyond 20 kHz. In situations where bandwidth is given as an audio specification, i.e. in frequency-response charts, the wider the bandwidth, the better.In audio electronics, we can compute the "Q", or Quality Factor for a filter using the bandwidth; the quality factor is defined to be the ratio of the center frequency Ä divided by the bandwidth.
Bantam - A description of patch cables and one of the primary types of connectors found on patchbays. The connector itself resembles a 1/4" phone plug, but it is slightly shorter and narrower, making it possible to squeeze more patch points into a given rack space than with 1/4" connectors.[A bit of history from Sweetwater InSync: Western Electric invented the Long Frame plug for telephone switchboards, which was eventually adapted into the 1/4" "phone" plug we find on the back of equipment these days. Switchcraft invented the "Tini-Telephone" plug, which was smaller and narrower. ADC, formed by a group of former Switchcraft employees, decided to register the name "Bantam" (from the boxing class) under which they could manufacture Tini-Telephone plugs.]
Bar - A unit of pressure equal to one million dynes per square centimeter.
Bass - Sound: the low-frequency end of the audio spectrum.Music: a musical instrument.Food: a fish, edible. We prefer Chilean Sea Bass coated in olive oil, garlic, and ginger, and placed in an aluminum-foil packet, and grilled to perfection.
Bass Reflex - A type of loudspeaker cabinet design in which a port, or opening, in the speaker cabinet enhances bass frequencies. The principle is that the sound wave pressure generated by the back of the speaker cone inside the cabinet can be routed out the port at the front of the cabinet, mixed with the sound coming from the front of the woofer. Changing the port size and position will greatly change the character of the low frequencies.
Beaming - A phenomenon found in all loudspeakers in which higher frequencies begin to be projected straight out of the loudspeaker rather than dispersing. The loudspeaker would sound as if the device only reproduces high frequencies when standing directly on-axis. Using horns for high-frequencies helps to alleviate the problem, and the advent of Constant Directivity horns improved the problem further.
Beat - A periodic variation in amplitude that is a result of the superposition or addition of two tones with nearly the same frequency- less than 30 Hz or so apart. It is most easily noticed when the original sounds are of equal volume. The frequency of the beats will be the difference in frequency between the two signals. We come across beats often in musical instruments, and are often used to facilitate the tuning of instruments-- when instruments are in tune, the beating stops-- but it is a phenomenon not restricted to musical instruments-- it can occur between any two signals.
Bel - Abbr. "b" or "B". Equivalent to ten decibels. The Bel was defined as the amount a signal dropped in level over a one-mile distance of telephone wire. See Decibel.
Bi-amping - A sound-system design process whereby the amplifiers are placed in the sound system after the crossover, one channel for low frequencies, one for high. Bi-amping produces a cleaner sound than if a single amp had been placed before the crossover. The crossover is not subject to high power levels and amplifier channels are dedicated to a certain frequency range whereby a channel can operate much more linearly, lessening distortion.
Bi-directional microphone - A type of microphone that is equally sensitive to sounds arriving from the front and back of its diaphragm, and relatively insensitive to sounds arriving from the sides.Also called a figure-8 microphone.

Bi-Radial Horn - A loudspeaker horn designed to reproduce high frequencies, in which the vertical and horizontal surfaces of the horn flare outward (although usually at different rates).See also Compression Driver, and compare with Radial Horn.
Bias - 1: Tubes- Bias is a small DC voltage applied to the tube's grid to operate the device at a more linear range in order to reduce distortion.2: Field-Effect Transistors- a small DC voltage applied to the gate to operate the device at a more linear range in order to reduce distortion.3: Bipolar Transistors- a small DC current applied to the base to operate the device at a more linear range in order to reduce distortion.4: Magnetic Tape- a very high frequency signal mixed with the audio signal during recording, thereby providing a signal that is always present so that the audio tape is fully saturated, in essence making the tape more responsive and more linear. Too little bias increases distortion; too much bias reduces overall signal level and diminishes high frequencies.
Binaural - A system of sound recording utilising a "dummy head" constructed out of plastic to emulate the shape and response of the human hearing system, with a microphone placed in each ear. The signal information recorded contains information regarding phase and directionality that would not necessarily be present in an ordinary microphone configuration. The signals from the two microphones are kept entirely separate throughout the mixdown and reproduction process, until they arrive at the two drivers of the listener's headphones. The result is a rather convincing preservation of the 360¡ sound field at the recording location.
Binding Post - A type of electrical terminal, binding posts are commonly found on outputs of amplifiers or the inputs of loudspeaker cabinets. The binding post can accept banana plugs, bare wire, and alligator clips, making it a very versatile connector; however, it is not lockable, which makes it unsuitable for portable applications.
Bit Mapping - The process of rearranging the digital data stream in such a way that information that would normally require a larger digital word can be encoded into a word of lower bit-depth, producing a higher quality signal than would normally be possible. Sony's Super Bit Mapping is an example of this sort of algorithm, which touts 20-bit performance on 16-bit recordings.
Blumlein Microphone (or Blumlein Pair) - Named for Alan Blumlein, an EMI London engineer during the 1930s, it is a stereo micing technique using two coincident bi-directional microphones set up at ninety degrees to each other. This technique provides for a strong center image and good ambience.
BNC - Connector: a type of coaxial connector often found on professional video and digital audio equipment, as well as on test equipment. It is a miniature bayonet locking connector designed for coaxial cable. In audio equipment, BNC connectors are commonly found to carry synchronization signals between devices and may occasionally be found carrying digital data. In video equipment, they are found carrying standard video signals.They are named for their type ("Bayonet"), and their two inventors, Paul Neill and Carl Concelman. A threaded type of BNC connector is available, called the "TNC Connector."
Boost/Cut Equalizer - The most common type of graphic equalizer, available with anywhere from five to thirty-one bands, on one-octave to 1/3-octave spacing (1/6-octave graphic equalizers are available, too). When each frequency slider is set to the "flat" (0 dB) position, they are at the center of their travel. By raising the slider in question, that particular frequency band is boosted anywhere from 0 dB to 16 dB, and by lowering the slider in question, that particular frequency band is attenuated. When a system has been equalized (or "tuned") using a boost/cut graphic equalizer, the resultant visual curve defined by the sliders on the front panel of the equalizer gives insight into the frequency response of the sound system in a given room.
Boundary Layer - Usually used in reference to microphones, the boundary layer is the region adjacent to a flat surface in which the phase shift between a direct sound wave and a reflected sound wave is negligible within the audio frequency spectrum. Certain types of microphones incorporate a flat plate immediately adjacent to the microphone diaphragm in order to achieve higher gain at the capsule-- the direct sound wave and reflected sound wave sum to provide a "stronger" sound wave.Also known as the Pressure Zone.
Boundary Microphone - A type of microphone design in which a small electret capsule is mounted close (< 1cm) to a flat plate, or boundary. The gap between the capsule itself and the plate is referred to as the "boundary layer." The sensitivity of the microphone is increased due to the microphone capsule receiving sound waves directly, and receiving sound waves that have bounced off the boundary plate. Since the distance the reflected sound waves travels is so close to the distance of the direct sound waves, the waves tend to reinforce each other.
Breathing - In the audio world, "breathing" is the audible change in level of a signal due to the use of noise reduction or other dynamics processing. For example, if a compressor is incorrectly set to operate upon a very dynamic audio signal, background noise may tend to fade in and out during soft passages as the compressor releases its grip.
Brickwall Filter - Commonly refers to certain types of low-pass filters which exhibit a steep cutoff slope which resembles a "brick wall." These types of low-pass filters are often found in A/D converters to prevent aliasing; while they are acceptable for this purpose their steep slope introduces unwanted side-effects on the audio signal, such as phase shift and non-linearity near the cutoff point.
Bridging - An amplifier technique by which a single input is fed to both channels of an amplifier, and the positive (+) output from both channels is summed into one, which provides for more amplifier power than using a single channel. Not all amplifiers will perform well when bridged, however.
Bucking - Usually known as "Phase Cancellation," bucking refers to the cancellation of one signal or part of a signal by another signal with equal amplitude but opposite polarity. This term is more commonly found in reference to musical instruments and used by musicians than "phase cancellation."Hum-bucking, which is type of guitar pickup, is the cancellation of hum frequencies (50 Hz in Europe, 60 Hz in the US), which is a result of induced EMI- electromagnetic inteference.

Bus - Public transportation definitions aside, a bus is usually referred to as a point in a circuit at which many signals are brought together. Many pieces of equipment have a ground bus at which all of the individual component's ground paths are tied together and thus connected to a single grounding point. In mixing desks, we have mix busses or subgroup busses, where multiple input channels are mixed together to form individual, discrete outputs, as well as auxiliary busses, which do pretty much the same thing.
Bus Bar - Usually a long rod of copper used to ground multiple electrical components to a single point. All internal components ground to the Bus Bar which then grounds to a single point outside of the chassis. Turn a Cadac J-Type frame upside down and open it up, and you'll see two long rods of copper, one for 0V, and one for ground.


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C Connector - Connector: a type of coaxial connector often found on radio equipment. Developed by Carl Concelman at Amphenol, it a bayonet version of the "N" connector.
Cable - Usually refers to a long, snakelike structure comprised of many copper strands woven together to form single conductors, which are then covered in a rubber, plastic, or, in the olden days, fabric insulation. Carries electrical signals of varying type.
Cam-Lok - A power connector devised by Crouse-Hinds specifically designed to carry large mains electrical currents. Used to connect power distribution racks or dimmer racks to mains power disconnects. One connector is used for each leg-- one per phase, one for the neutral, and one for the ground.
Capacitor - An electronic circuit element, also called a condenser, that stores electrical energy much like a battery by creating an electrical field between two conductors, usually two plates separated by an insulator. DC current cannot flow through a capacitor, but AC can flow between the plates to a limited degree. At a specified parameter and after a given length of time, based on the characteristics of the insulation and electrical signal, signal will flow through the insulator.
Capstan - A mechnical portion of a magnetic tape recorder. It is the rotating shaft that drives the tape past the tape heads. Usually the tape is sandwiched between this shaft and a rubber wheel called the pinch roller. The capstan is what controls the speed of the tape across the heads.

Capsule - Space-travel definitions aside, it is a name given to the transducer element in a microphone which contains the mechanical structure to convert the acoustic sound pressure waves into electrical current.

Cardioid - A microphone pickup pattern, often referred to as a unidirectional microphone (although this is true, there are other types of unidirectional microphones). A microphone with a cardioid pickup pattern is characterized by strong sensitivity to sound pressure waves from the front of the microphone, decent sensitivity from the sides (which is defined as 6dB less than the front at 90 degrees off-axis), and good rejection from the rear. It is so-called due to the heart-like shape of its polar pattern. Cardioid microphones are commonly found as handheld microphones and are used in situations where it is not ideal to have a great deal of room ambience. Vocalists use cardioid microphones due to its ability to reject signals from the rear of the microphone and because all unidirectional microphones exhibit proximity effect, an increase in low frequencies as the microphone is placed closer to the sound source.
Cart Machine - A magnetic-tape playback system slowly going the way of the dodo. Short for "tape cartridge machine," it is a playback machine that uses endless loops of magnetic tape in plastic cartridges. Used most often in broadcasting for commercials and announcements, the cart machine also found a niche in theatrical sound playback. While many are still in existence, newer technologies have taken over: MiniDisc, Compact Disc, 360 Systems DigiCart, etc., etc.
Cascading - Waterfall definitions aside, the act of connecting two or more mixing desks together in order to extend the number of inputs or outputs available.
Catwalk - A walkway usually suspended or cantilevered in the air. A term sometimes given to a fly gallery, loading platform, or a lighting position in the auditorium.
CCIR - French, abbreviation for "International Radio Consultative Committee". A branch of the International Telecommunications Union (ITU), a specialised agency of the United Nations, concerned with the generation of documents relating to radio signals.
Cent - One one-hundredth (1/100) of a semitone. A common and convenient way of describing very small increments of pitch in musical terms.
Channel Fader - The level control, usually in the form of a slide fader but sometimes as a rotary potentiometer, on a mixing desk which affects the level (volume) of that particular channel with respect to the rest of the inputs. Often just "fader."
Channel Path - In a mixing desk, the channel path is the audio signal path from the physical input (microphone or line) to the point at which the audio signal is combined with other incoming signals, i.e. after the channel fader, the equalisation section, etc., etc.
Channel Separation - In a mixing desk, it is the lack of crosstalk, or bleed of audio signals from one channel to another, between channels. A low crosstalk specification indicates high channel separation.

Chorus - Music:-a composition in four or more parts, written for a number of singers.-a refrain in which a number of singers join a soloist in a song.-a solo section in a song based on the main melody and played by a member of the group.-a body of singers who perform choral compositions.Drama:-a body of vocalists and/or singers who support the leading performers in operas, comedies, etc.Sound:Also "Chorus Effect." A non-linear signal processing effect that is the combination of direct sounds and several delayed and phase-shifted replicas to simulate the effect of a traditional chorus. Some processors combine the direct sounds with pitch-shifted replicas which are modified in amplitude and phase to create a similar effect.
Circumaural - Trans: "Around the Ear." Used in reference to headphones, circumaural headphones encircle the ear and often seal the ear within the cup of the headphone, providing for good isolation from outside noise.
Click Track - A metronomic pulse heard in monitor headsets by musicians or conductors during the performance of music. The purpose of a click track is to guide the musicians for sake of timing consistency. In film scoring click tracks are used to ensure that musicals "hits" and effects happen at the proper moment, timed to the picture. In theatre sound, click tracks are often used when a prerecorded section of singing is played back with the live performers; the click track pulse leads the conductor, who in turn leads the live performers and the orchestra so that everyone is synchronized. Can also refer to the actual recording of live performers for the intent of being used as a click track.

Clipping - Distortion in an electronic device due to severe overloading. If the device in question cannot accommodate the voltage or current being passed, the waveform of the signal is sometimes said to be clipped, because of the graphical representation of the audio signal looking as if the peaks were clipped by a pair of scissors. A clipped waveform usually contains a great deal of harmonic distortion and sounds very rough and static-like.

Close Micing - A microphone placement technique in which the microphone is placed near a sound source (1" - 3'), effectively eliminating all but the direct sound of a source.
Cluster - Refers to a collection of two or more loudspeakers, rigged side-by-side or top-to-bottom or both. More specifically, it is usually used to denote a centrally hung loudspeaker array.

CMRR - "Common Mode Rejection Ratio." Describes the integrity of a balanced circuit. In balanced lines, there is always a positive signal on one conductor, and a negative signal on the other. Any signal that is common to both wires (i.e. induced noise in a microphone cable) will eventually be canceled at the receiving end. The degree of cancellation at the receiving end is dependent on the integrity of the circuit, and the CMRR defines to what degree the signals are canceled.
Coaxial Cable - A cable comprised of a single copper conductor, surrounded by a layer of insulation, and covered by a surrounding copper shield and flexible jacket. Often referred to as "coax," they are used for high-frequency transmission of RF signals and more recently have come into use for high-frequency digital audio signals. The construction of the cable is designed to keep a specific distance between the inner, signal-carrying conductor and the outer shield, which is one factor in defining the impedance of the cable. Due to the high frequency nature of RF signals and digital audio data streams, impedance becomes critically important because of the bandwidth involved.
Codec - Abbrevation for "Code/Decode" or "Compression/Decompression." Originally a device used in the telecommunications industry for converting voice signals from analog to digital for use in digital transmission schemes (over fiber-optics, GSM mobile, etc.), and re-converting them back to analog. The term is now used to include the conversion of analog video and audio signals into a digital form and the subsequent compression of these signals to conserve bandwidth. Most codecs used for video and audio signals use a proprietary conversion algorithm scheme.
Coincident - A microphone placement technique, "coincident" usually refers to stereo microphone pairs. In coincident micing, the capsules of two microphones are placed as close together as possible to avoid any phase-cancellation problems in the final mix. In traditional coincident placement, two cardioid microphones are placed at an angle of 90 degrees to each other, with their capsules "stacked" atop each other.The "MS" or "Mid-Side" microphone technique falls into the coincident microphone technique, but uses one bidirectional (figure-8) microphone, and one cardioid microphone. By using a special matrix at the outputs of the microphones, the apparent "width" of the stereo field can be adjusted.
Coloration - A term used in sound to indicate audible alterations to the sound arising from environmental conditions or the equipment used.

Comb Filter, Comb Filtering - A comb filter is a filter that has a series of deep notches in its frequency response which correspond to multiples of the frequency of the lowest notch. When plotted on a logarithmic frequency graph, the structure looks like a comb. Comb filtering is produced through a variety of ways; in studio recording the use of phasers and flangers and multiple delays create comb filtering, in which some frequencies will cancel each other and other frequencies will reinforce each other, changing the tonality of the sound. Interestingly enough, while it can be a desirable effect in studio recording, comb filtering is eschewed in sound reinforcement-- when a multiple loudspeaker system is used, interaction between loudspeaker cabinets (with similar program) will create comb filtering in the listening area, due to differences in arrival times. Repositioning of loudspeakers, addition of delay, and proper use of equalization are all tools to reduce the audible effects of comb filtering.
Compander - A contraction of "compressor" and "expander." A signal processor which manipulates dynamic range in order to reduce noise or bandwidth, the signal is first compressed before distribution (to tape or through a broadcast system) and expanded at the reproduction end. As the signal is expanded, inherent noise in the playback or distribution medium tends to be "pushed down," resulting in a quieter signal.

Compression Driver - A loudspeaker component designed to reproduce high frequencies in place of moving-coil tweeters. A small voice coil is attached to a diaphragm (nothing new here) whose surface propels sound into the horn via a small opening called the throat; hence the name "compression" driver. The high pressure sound waves traveling out of the throat interact with the low pressure area of the horn, and radiate sound quite efficiently. This construction is more efficient than standard horn design, and is attributed to Bell Laboratories.

Compressor - A signal processing device in which the dynamic range of the output signal is less than that of the input signal-- in other words, a compressor reduces the dynamic range of an audio signal. Compressors were first developed in the early days of phonograph media and telephone distribution technology, in which the audio signal to be transmitted had a greater dynamic content than could be handled by the media of the time. The threshold of the compressor dictates at what point (in dB) the audio signal should be compressed. The ratio of the compressor dictates the amount of reduction of the audio signal-- for example, with a 4:1 ratio, for every four dB of gain over the threshold value, the output signal is allowed only one dB of gain increase. A variety of other controls are available to affect the way in which the compressor affects the audio signal-- the attack time and release time, for instance, set the speed at which the compressor acts upon a given signal that is over its set threshold and subsequently lets it go.Compressors are widely used in popular music recording, where they are used on single tracks or instruments in order to "fatten" sounds or even out vocal tracks or "tighten" drum tracks. In live sound, they may be used in popular music performances for much the same effect. In theatrical sound, however, the use of compressors is mostly eschewed, as the use of the compressor defeats the purpose of the human operator and generates a non-linear audio signal.

Condenser Microphone - A design of microphone capsule in which a capacitor (or condenser) is created by stretching a thin conductive diaphragm in front of a metal disc called a backplate. By positioning the two surfaces very close together, but not touching, a capacitor is created whose capacitance varies as the sound waves strike the diaphragm and change its physical relationship to the backplate. The electric charge required for this process to occur is provided by an external source, such as a power supply unit or phantom power delivered from the mixing desk. Condenser microphones have very few moving parts but are susceptible to shocks; however, their sensitivity and electrical characteristics far outweigh any detriments, and are the preferred choice of microphone when micing musical instruments or the human voice.

Console - Also: Mixing Console, Mixing Desk, Desk, Sound Desk, Mischpult, Sound Board, etc. The central electronic system to which multiple audio input signals are routed for level control and signal processing, and for combination with other audio input signals and subsequent routing to various audio outputs.

Constant Directivity - Refers to a type of loudspeaker design in which the reproduced sound does not become more directional as the frequency rises. An inherent characteristic of high-frequency drivers is the tendency to, as frequency rises, appear more directional and lose the desired dispersion characteristics. A constant directivity horn, for example, attempts to alleviate some of the directionality.
Constant Q - A term applied to graphic and parametric equalizer units. On some equalizers, changing the gain of a particular frequency band also changes the "Q" or bandwidth of that band. This increases the overlap between adjacent bands. In equalizers with "Constant Q" or "Constant Bandwidth," the bandwidth remains constant no matter how far the gain is boosted or cut. The use of a Constant Q equalizer is preferable because the effect of the equalizer is better predicted.

Constant Voltage System - An interface between power amplifiers and loudspeakers primarily used in distributed sound system installs, such as airports, stores, factories, and schools, where a single amplifier (or a few amplifiers) is driven at its maximum output voltage (70.7V in the USA, 100V in Europe), and step-down transformers are used at each loudspeaker to control volume level. Using this high-voltage (low-current) and high-impedance distribution system allows for the signal-carrying cable to be very small in diameter, which allows for cable runs of long distances. However, sound quality may suffer due to the use of transformers at the loudspeakers. The system was derived from the need to minimize cost and simplify design of extended audio systems.The name is derived from the idea that the power source (amplifier), will be supplying a fixed amount of voltage at full power; no matter how the impedance may change (i.e. adding or removing loudspeakers from the chain), the voltage remains the same.
Constructive Interference - The interaction of two or more identical sound waves which support, or reinforce each other. Compare with "Destructive Interference".
Contour Control - A term applied to some professional DJ mixers used to change the shape (or taper, or contour) of the fader action-- mostly in reference to the travel of the crossfader. For instance, at 50% of travel, a fader may allow 50%, 20%, or 80% of the audio signal to pass depending on the taper of the control. Most faders have a logarithmic curve to easily plot the way in which the human ear responds to changes in loudness in terms of decibels.Also "Fade Profile."
Control Voltage - In audio electronic circuits, a control voltage is a DC voltage that is proportional to a given audio signal. Varying the control voltage varies the level of the audio signal in question. For example, in mixing desks with VCA master faders (also called DC master faders), no actual audio travels within the faders-- instead, a control voltage proportional to the physical position of the input fader controls the audio signal found elsewhere in the mixing desk.
Coupling - In electronics, "coupling" refers to ways of connecting circuits or circuit subsystems to one another.In acoustics, "coupling" refers to the interaction of two separate loudspeaker systems and their resultant constructive interference, where sound waves of a particular frequency and phase may reinforce each other.
Coverage Angle - The included angle between the points on either side of a loudspeaker axis at which the response is attenuated by 6dB with respect to the on-axis level. Applies on some level to the same included angle on either side of a microphone axis at which the response of the microphone is attenuated by 6dB. Also see "Dispersion" and "Polar Patterns."
Critical Distance - In acoustics, the distance from a sound source at which the direct and reverberant sound energies are equal.
Crossfade - Music / Sound Editing: a technique commonly used in audio editing, in which one sound is faded out as another fades in, allowing for a seamless transition between the two sounds. Samplers use crossfades when looping a patch in order to prevent any sort of annoying "clicks" or "pops" at the beginning of the material, and may also use them to fade between two different sample patches-- "morphing" them, if you will.DJ: Often associated with disk-jockeys, to "crossfade" is to gradually mix, or blend, two independent stereo signals, one at the beginning of its material, and one at the end. The ultimate goal is to create a seamless transition between two different pieces of music. The crossfader is the potentiometer that allows this transition to occur. At one extreme of the crossfader travel, only one program source is fed to the output; at the other extreme, the other program source is fed to the output. In the middle, the crossfader mixes the two program sources, usually maintaining equal power during the transition. Compare with "pan" and "balance" controls.

Crossover - An electrical circuit, often found as an actual component of a loudspeaker system, that separates parts of the audio signal into frequency bands suitable for specific loudspeaker components. Since audio wavelengths vary from over fifty feet at extremely low frequencies to less than one inch at high frequencies, a single loudspeaker driver cannot reproduce the entire range of the audio spectrum, and more drivers, dedicated to specific bands of the audio spectrum, are used together to reproduce the full spectrum.A crossover is essentially a high-pass filter and a low-pass filter in parallel; audio frequencies higher than that of the crossover point of the two filters pass through the high-pass filter and to a high-frequency loudspeaker component (or amplifier for the high-frequency component) and frequencies lower than that of the crossover point pass through the low-pass filter and to a low-frequency loudspeaker component. Passive crossovers are components that are placed inside the loudspeaker cabinet, after the amplifier, and active crossovers are standalone units that are placed before the amplifier in bi- or tri-amplified loudspeaker systems, so an individual channel of amplification is dedicated to only reproducing a certain subset of frequencies, often resulting in a cleaner audio signal.Crossover circuits are characterized by their type (Butterworth, Bessel, and Linkwitz-Riley being the most popular; we won't get into those now), and by how steep the rolloff is at the cutoff (crossover) frequency. Common configurations are 12dB per octave, 18dB per octave, and 24dB per octave. Each design has its own strengths and weaknesses; in general the steeper rolloffs are considered better.

Crossover Distortion - A type of distortion which does not relate to loudspeaker crossover units; it is a type of distortion occuring in electrical circuits when an audio signal waveform "crosses over" from the positive side to the negative side. In push-pull amplifier designs (popular tube-amplifier design), separate output devices handle each half of the audio waveform; if the handoff near zero (where one device transfers its responsibility to the other output section) is not completed smoothly, distortion can occur.
Crossover frequency - In a crossover network, the frequency at which the outputs of the two adjacent filter networks are both attenuated by 3dB, which happens to be the cutoff frequency of the crossover unit.

Crosstalk - Refers to any undesirable leakage between two channels-- channels of multipair cable, channels on a mixing desk, tracks on magnetic tape, channels of intercom, etc. In electronics, also refers to undesired inductive, capacitive, or conductive coupling from one circuit or channel to another.

Cue - Music: a section of music used in film or video production.Music: in a musician's score, an extract from a prior section of music, usually in smaller notes, as a signal to the musician on when to enter after a tacet.Music: a gesture by a music director, conductor, or other musician to signal the entrance of another performer.Theatre: a signal, given as a word (usually "go") or a light, used to signal an entrance or an action, such as a change in lighting or playback of a sound effect.Sound: refers to a sound effect, or a change in system status, such as within mixing desk automation.Sound: can refer to an audio signal sent to musicians onstage or in the studio which allows the musicians to find their bearings and thus their entrance in a piece of music. Often called a "cue mix," but later changed to "monitor mix."DJ: refers to a switch similar to the audio engineer's PFL switch, which allows the DJ to listen to a specific input before presenting it to the audience.
Cue Monitors - A small speaker or a pair of headphones used by the operator specifically for cueing microphones, instruments, or recorded media before raising the level to the house sound system.

Current - Electricity. Symbol: i or I. Measured in Amperes, or "amps." Current is defined as the flow of electrical charge produced by an electrical charge (voltage), or, in other terms, the amount of electric charge flowing past a specified circuit point per unit time.
Cut-only Equalizer - Also: "notch equalizers" or "band-reject equalizers". A type of (usually) graphic equalizer designed only for attenuation of frequencies. A cut-only equalizer is comprised only of notch filters; all controls start at 0dB and reduce the signal on a per-frequency basis.
Cutoff Frequency - In a filter, the cutoff frequency refers to the frequency at which the audio signal falls off by 3dB (half the power point) from its 0dB maximum value. Beyond this cutoff frequency, the filter will attenuate all other frequencies.


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D-Sub, D-Connector - Connectors: used to describe a type of multipin connector often used in audio and computer applications. Originally designed by ITT-Cannon, and given the "D" designation, they are available in different pin-outs and pin-types. The DB-25 connector is often used as a serial and/or parallel port connection; DA-9 connectors are often used as VGA monitor siganls, etc., etc., etc. "D-Sub" is the common tag given to the connector by other manufacturers.

D/A Converter - Also: "DA Converter;" short for "Digital-Analog Converter" and abbreviated "DAC." An electronic device which converts a digital binary data stream into an analog audio signal-- doing exactly the opposite of an A/D Converter. Most digital recording equipment and digital processing equipment have such converters built in, although standalone units are available. See Digital Audio text for complete explanation of how they reconvert the signal. Also note that DACs need not convert digital data into audio; they can also refer to similar components used in telecommunications, video, etc., etc.

Damping - Physics: refers to loss of energy in a vibrating system, usually lost through friction. Sound: see Damping Factor.
Damping Factor - Damping is a measure of an audio power amplifier's ability to control the back-emf motion of the loudspeaker once the signal dissipates. When, for instance, a speaker cone continues to move after the electrical audio signal stops, it tries to drive the output of the power amplifier, resulting in less-than-pleasant effects. Designers of power amplifiers thus try to present a "dead-short" to the loudspeaker: the damping factor is defined as the ratio of the loudspeaker's nominal impedance to the total impedance driving it (amplifier + speaker cable). A high damping factor states that an amplifier's output impedance can absorb the electricity generated by the speaker cone motion, which will thus stop the loudspeaker's vibration. Effects of damping are most evident at lower frequencies; well-damped loudspeaker systems sound "tighter" at the low end because the woofer is not allowed to resonate after the electrical impulse is gone.For all you math geeks out there, refer to some other website if you want to know how to calculate the damping factor.
DB-25 - Connectors: a twenty-five pin connector standardized for RS-232 serial communications. "D"-shell configuration.
DB-9 - Connectors: a smaller nine-pin version of the DB-25 connector used for RS-232 serial communications.
De-Esser - A sound system component, usually found in recording studios and occasionally in installed audio systems, which is a frequency-dependent compressor, tuned to be sensitive to sibilant sounds-- sounds with high frequencies such as the sound produced by saying the letter "s". While some microphones are equipped with a "presence peak" to boost the mid-to-high frequencies for increased intelligibility and more "air," the presence peak can undesirably boost frequencies to a point where it is annoying, or, even worse, to a point where sibilant sounds can cause audible distortion in the audio path.Early de-essers were composed of an equalizer and a compressor with a sidechain input. The offending frequencies were boosted on the equalizer, and the equalizer output connected to the sidechain input, which, with some tweaking, told the compressor to only start compressing when the offending frequencies went over a preset threshold. Newer de-essers are capable of compressing only the offending frequencies, instead of the entire audio signal, and some manufacturers produce processors specifically designed for vocalists, which combine the effects of a de-esser, an equalizer, and a compressor in one handy box.
Decay Time - Defined as the time it takes for the sound pressure level of room reflections (reverberation) to drop in SPL level by 60 dB from their original strength. Often called "reverb time," and abbreviated Rt(60).
Decca Tree - A stereo microphone placement technique. Three omnidirectional microphones are placed in an inverted "T" arrangement; two microphones are spaced about two meters apart, and a third is placed between the two, but about one-and-a-half meters forward.
Decibel - Abbr. "dB." Originally a measuring system developed and used by the telecommunications industry, referring to one-tenth of a Bel. Most commonly used in audio practices to represent a ratio between two different audio levels. It is important to note that the decibel is not an absolute number, but always refers to a ratio of two numbers. It is used so extensively because it is very easy to represent both very small and very large changes in relative levels. Because it is merely a ratio, a decibel alone has no units, and always must be related to some reference point, which is designated by a letter following the "dB" indication.0 dBu is a voltage reference point equal to 0.775V, rms. Pro audio voltage for line-levels is defined as +4dBu.0 dBV is a voltage reference point equal to 1.0V, rms. Consumer audio voltage for line-levels is defined as -10dBV.0 dBm is a power reference point equal to 1mW.0 dBFS is a reference level which represents the maximum level in an AD or DA converter possible before clipping.There are other variants beyond the scope of this definition. See Basic Terms for more information.

Delay - A type of audio signal processing device used to delay one or more outputs by a user-definable amount. The uses of delay lines are thousandfold, for instance: Loudspeaker signal processing- a delay line can be used to correct for loudspeaker drivers that are not time-aligned; that is to say, that the drivers are not physically aligned in the same plane.Musicians- delay lines are often used as the basis for many off-the-shelf effects pedals and boxes that guitarists, vocalists, keyboardists, etc., use.Sound reinforcement- sound designers, contractors, and acousticians use delay lines to provide proper imaging when installing large loudspeaker systems.
Destructive Interference - The interaction of two or more identical waves which do not support, and often cancel or interfere, with each other. Compare with "Constructive Interference."
Diaphragm - Medical definitions aside: the physical, moving element of a microphone capsule that converts physical, sound-wave energy, into physical mechanical energy (which is then converted into electrical energy in the microphone capsule).
Diffraction - The manner in which sound can bend around obstacles.
Digital Audio Workstation - Abbreviated "DAW." Refers to any sort of computer-based system for editing, recording, and playback of audio signals. Emagic's Logic Audio and Digidesign's ProTools are examples of DAW systems.
DIN - Acronym for "Deutsche Industrie Normung" or "Deutsche Institute fŸr Normung" or "Deutsche Industrie Norm," it is a German organization that establishes standards for industry, similar to the Japanese JIS, or American AES or IEEE, or European EBU. In audio, it is common to find DIN specs in regards to connectors-- circular multipin connectors, such as those five-pin cables used as MIDI cables, are based on the DIN standards. Apple Computer's ADB and serial ports use a variation, often called "Mini-DIN."DIN also sets standards for equipment electrical characteristics, which may not necessarily correspond to standards developed by other nations.
DIN Stereo - A stereo microphone placement technique. Two cardioid microphones are placed approximately 20cm apart with the capsules angled at 90¡ to each other in order to replicate the stereo image. Used at close ranges, it can be a very effective recording technique.
Diode - An electrical circuit component that allows easy electrical current flow in one direction only.

Direct Box - A small device, usually in the form of a small box, used to convert an unbalanced, high-impedance speaker- or instrument-level output to a balanced, low-impedance mic-level output. The use of a direct box enables an electronic-instrument level signal, such as a guitar or keyboard output, to be delivered along long distances as if it were a low-impedance balanced microphone to the mixing desk, averting possible tonal quality shifts due to impedance mismatching. Simple direct boxes usually consist only of a transformer, while so-called active direct boxes have electronic gain stages and various switches to control gain, grounding, and equalization.Often abbreviated "DI," for "Direct Injection".

Direct Current - Electrical current that flows in one direction only; the opposite of Alternating Current (AC), which flows in alternating directions according to its frequency (an audio signal is an example of alternating current). Direct Current is often used to provide power to electrical components.
Direct Injection (DI) - A sound system interconnection process in which an electrical audio signal is taken from a musical instrument to the mixing desk via a direct box. Used instead of acoustically micing an instrument amplifier.
Direct Out - A feature found on some mixing desks whereby a separate output is fed directly from the preamplifier stage of the input, independent of fader level and equalization, which can be sent to a monitor mixer or recording desk.
Dispersion - Also "Dispersion Angle." The angle of effective coverage for sound radiated from a loudspeaker, defined as the included angle bounded by the points at which the loudspeaker's SPL level drops six decibels from its on-axis response. Loudspeaker specifications will provide two components, horizontal dispersional angle, and vertical dispersion angle. Similar to "Polar Pattern."
Distant Micing - A microphone placement technique in which the microphone is placed at a distance (3' or greater) from the sound source in order to pick up a larger portion of the overall instrument sound and/or reflected and ambient sound. Not recommended for many sound reinforcement applications, due to low gain-before-feedback.
Distortion - Electronics: refers to a measure of the difference between the output and input signals in a linear component, such as an amplifier.Sound: an undesirable, audible effect, usually due to the overloading of one or more components, which results in "dirty" sound.Harmonic Distortion is a classic example. Intermodulation Distortion fits the technical definition of distortion, but does not necessarily result in "dirty" effects, but refers to an undesirable change in the audio waveform.
Distribution Amplifier - Abbrev: "DA". A distribution amplifier is a low-power amplifier, usually running at line-level, designed to split a balanced input signal into several outputs with high-current line drivers capable of driving very long cable lengths. For example, stereo outputs of a mixing desk may be run into a distribution amp, at which they would be split to simultaneously feed a press feed, a DAT recorder, a cassette deck, et al. Using a distribution amp prevents potential problems caused by "Y"-ing, or passively splitting, a single output to feed multiple inputs.
Diversity - Applying to radio-frequency (wireless) microphone systems, it is a radio-frequency reception system in which two antenna positions are used per unit. The receiver identifies which antenna position has a stronger rf signal from the transmitter and uses that antenna at that given moment in time.

Dome Tweeter - A type of loudspeaker tweeter (high-frequency transducer) with a lightweight cone, or dome, often fabricated from paper, acting as the diaphragm of the transducer. Characterized by their clear and flat response, but unable to withstand great amounts of power. Compare with Compression Driver.

Doppler, Doppler Effect - The Doppler Effect, named after Austrian physicist Christian Johann Doppler, it is the perceived change of the pitch of a sound that occurs when the source or the listener is in motion. Often best heard as the phenomenon when the perceived pitch of a train whistle starts high and gets lower as the locomotive approaches, passes, and moves away from the listener.Doppler Distortion is defined as the modulation of the high frequencies by the low frequencies, and is often found in loudspeaker drivers designed to reproduce the full range of the audio spectrum. The low frequencies cause the loudspeaker diaphragm to physically move forwards and backwards, which modulates the high frequencies the loudspeaker is also producing, pitching them alternatingly higher and lower, according to the low frequencies.
Ducker - An audio signal processor, based on a compressor, that reduces ("ducks") the level of one audio signal based upon the level of a second audio signal. Typically used in industrial installations where it is necessary to override program material with paging messages.
Duplex - A communications term referring to simultaneous, two-way communication in both directions. Also called "full duplex." Compare with "half-duplex."

Dynamic Microphone - A type of microphone capsule design in which an electrical audio signal is generated by a voice-coil or ribbon (called a diaphragm) moving within a permanent magnetic field. The diaphragm moves in response to actual sound pressure waves; moving within the magnetic field causes changes in magnetic induction, which comprise the audio signal. This type of transducer operates almost exactly like a standard loudspeaker, except in reverse.Dynamic microphones are often chosen in sound reinforcement applications due to their durability, expense (generally, they are the least expensive type of microphones), and ability to withstand very high sound pressure levels.

Dynamic Range - Simply, the ratio, expressed in decibels (dB), between the lowest, or softest, and highest, or loudest, undistorted level a system is capable of handling, or the level a system is capable of providing. An orchestra, for example, may have a dynamic range of 110 dB SPL, meaning that the softest passages are 110 dB SPL less powerful than the loudest ones. The dynamic range of electronic equipment is a function of the maximum output level and the noise floor: professional-grade mixing desks, for instance, can output maximum levels of around +30 dBu, with the lowest noise floors around -96 dBu, which provides a 126 dB dynamic range.It should be noted that analog equipment does not necessarily have a static maximum output level. Maximum output level in analog equipment is thus usually measured according to the highest output level without exceeding somewhere between 1% and 3% distortion.
Dyne - Physics: a unit of force, equal to the force required to impart an acceleration of one centimeter per second per second to a mass of one gram. Often seen in older acoustics texts.

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Comments, Questions, and Additions should be addressed via e-mail to Kai Harada. Not responsible for typographical errors. - © 1999 Kai Harada. 07.11.1999.

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