Sound Glossary

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EBU - Abbrev. f. "European Broadcast Union." A professional technical society that helps establish broadcast, audio, video, and telecommunications standards in, yup, you guessed it, Europe. Similar to AES.
Echo - Acoustics: One or several distinct repetitions of a sound created by reflections and the acoustic nature of a given space. Sound/Music: One or several distinct repetitions of a sound. Can apply to an audio processor designed to digitally recreate this effect.
Effects Send - On a mixing desk, an output separate from the main outputs which are designed to feed an external signal processing system; generally, each input channel will have the necessary controls and electronics to perform this task. See Auxiliary.
EIA - Abbrev. f. "Electronic Industries Association." The EIA is a trade organization comprsied of worldwide electronics manufacturers which sets standards which have become the de facto standard in electronic specifications.
Elco (or Edac) - Connectors: a brand and type (like "XLR") of multipin connector, often found in recording studios and broadcast trucks. Elco connectors are made in the USA, and Edac in Canada, but they are interchangeable. As with most connectors, they are available in a variety of pin configurations, male and female genders, and cable-end or panel-mount varieties. They are generally not used in live sound because their strain-relief leaves much to be desired, and are best left to controlled, fixed installations.
Electret - A type of microphone design, similar to the condenser. Instead of using a polarizing plate, which requires an external power supply to operate, there is a permanently charged plate made with an electret, an acronym for "electricity" and "magnet." As the diaphragm moves in response to sound pressure waves in close proximity to the electret plate, capacitance changes (this is exactly the way a standard condenser microphone operates, and thus you will also see the words "Electret Condenser" to describe electret mictrophones). The benefit of this design is that it does not require a separate power supply to charge the plate, although many electret microphone designs require a voltage to power a built-in impedance converter (usually a small FET transistor in the capsule itself).
Electro-Magnetic Interference (EMI) - A type of audible interference caused by large power current flowing through cables in close proximity to audio equipment or cables. The magnetic field around the power cables permeates the audio cables, resulting in undesirable hums or buzzes. Switching dimmers, fluorescent light ballasts, neon lights, flicker lights, computers, and RF transmitters are all generators of EMI. Careful routing of audio cables and adherence to EMC standards can alleviate the problem. [Audio cables are not the only cables susceptible to EMI; data cables, often a source of EMI, can also be adversely affected by EMI.]
Electromagnetic Interference - abbrev. "EMI." Refers to interference in (audio) equipment produced by components within the equipment, produced by components in close proximity to the equipment, or via cable runs picking up electromagnetic fields. Such fields can be produced by fluorescent lights, fluorescent ballast, high-current power lines, computers, ignitors, video monitors, RF transmitters, and most types of theatrical lighting dimmers, and usually manifests itself as hum, static, or buzz. Methods for alleviating the effects of EMI include shielding in audio cabling, proper grounding schemes, the use of twisted-pair balanced audio circuits, isolation transformers, and physical repositioning of equipment.
Envelope - The time variation of the amplitude of a vibration. A term commonly found in synthesizer and tone-generator discussions.
EQ Cut - On a mixing desk, a button which disengages the mixer's equalization circuitry, usually on a given channel, enabling the original sound to be compared to the equalized sound. Also applies to similarly-functioning buttons on standalone equalizers.
Equalizer - An audio signal processing device used to modify the frequency response of an audio signal. Originally designed by the telecommunications industry to "equal" out the frequency response through long transmission lines or in early cinema sound playback (hence the name), the equalizer is constructed out of a network of filters with set or adjustable center frequencies. Equalizers can be passive, and attenuate frequencies only, or active, which attenuate and boost frequencies; fixed equalizers have preset center frequencies, while adjustable frequency equalizers have sweepable center frequencies. Several types of equalizers are available:Graphic equalizers have slider level controls at preset frequencies, and no control for the bandwidth of the attenuation or boost. One set, the sliders graphically represent the response curve, but not very accurately.Parameter equalizers have separate controls for center frequency, bandwidth, and boost/cut. This type of equalizer is preferred because it provides greater control of boost/cut than a graphic equalizer because the user is not restricted to the fixed frequency choices in a graphic equalizer, but novices are intimidated by all the knobs.Paragraphic equalizers are parametric equalizers with slide-fader control of boost/cut at each filter. Very rarely seen in practical use.Cut-only equalizers (or "notch equalizers" or "band-reject equalizers") are usually graphic equalizers designed only for attenuation; they are passive devices.All-pass equalizers (or "phase-delay" or "signal-delay" equalizers) are equalizers that do not attenuate or boost any frequencies. Their sole purpose is to change the phase response of the audio signal. All filter networks introduce phase shift over different frequencies; by merely inserting an equalizer with no boost or cut, the phase response of the audio signal changes.
Exciters or Enhancers - A dynamic signal processor used often in recording and occasionally in performance, designed to enhance the existing program material. Exciters add harmonic distortion in controlled amounts to alter the listener's perception of the material. The study of psychoacoustics has shown that odd-numbered harmonics tend to make audio signals brighter, whilst even-numbered harmonics tend to make audio signals warmer. Low-order harmonics control the basic timbre of the sound, whilst high-order harmonics control the bite of the sound. (Rane).

Expander - A signal processing device in which the dynamic range of the output signal is greater than that of the input signal-- in other words, an expander increases the dynamic range of an audio signal. Expanders were developed in response to compressors, which were required for signal transmission in broadcast and telecommunications; the expander at the receiving end of the broadcast un-compressed the signal, in the hopes that the original dynamic range of the signal would be restored. Modern expanders are used extensively in noise reduction, which is termed "downward expansion" since they do not necessarily affect the higher amplitude signals. In downward expansion, a threshold is set on the expander which is below the average audio signal but above the noise floor. When an audio signal falls below the threshold, the expander kicks in and pushes the signal even further down, reducing the level of noise. For example, with a 1:2 ratio, for every 1dB of input level change, the expander will output a 2dB change. If an input signal drops below the threshold by 3dB, the expander will output a 6dB change, resulting in noise reduction improvement.


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Fade Profile - 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 "Contour." Can also apply to automated mixing desks, in which timed fade-ups or fade-downs can be faded according to a logarithmic scale, or a linear scale.

Fader - A type of variable attenuator or potentiometer in which the degree of attenuation or gain is dictated by the physical position of a given point over a straight path. Used mainly in reference to the actual audio signal level control on a mixing desk, which dictates the amount of audio signal from the input channel bussed to the output sections.
Faraday Shield (or Faraday Cage) - A metal shield, or cage, constructed of some conductive metal, which is placed around an electrical component and connected to ground in order to protect the component from unwanted external noise (in the form of radio-frequency interference or electromagnetic fields) from penetrating the component inside. The shield on a balanced audio cable is an example of a Faraday shield.
Fast Fourier Transform - A long time ago (approximately 150 years ago), Austrian Baron Joseph von Fourier was the first scientist to publish than any complex sinusoidal signal (such as that of an audio signal) could be mathematically represented by infinite series of sine functions by treating small portions of the waveform as periodic. A Fourier series is an infinite series of sine functions of the form 1/n (sin) nx, where "n" is an integer, and "x" is an angle. This original algorithm is known as a Discrete Fourier Transform, and it wasn't until the 1960s that scientists revisited how to calculate a Fourier Transform, and the new method was termed "Fast Fourier Transform," because it was more efficient than Fourier's original method. These days, computers can perform many of these calculations very quickly, even in close-to-real-time. Computer measurement systems such as Meyer Sound Labs' SIM System II can display a much more accurate representation of the audio signal than a real-time spectrum analyzer. Meyer's SIM System is revered for not only its accurate frequency analysis, but it also provides comprehensive phase information about the audio signals. (Thanks to Simon Turnham for revising my definition; for further information on the Fourier Transform, check out

Feedback - Defined as the return of some of the output back into the input of a system. In electronics, a feedback circuit is a circuit design in which a portion of the output signal of an amplifier is sent back into the input. "Negative feedback" is the state in which the output signal is inverted in polarity before being sent back to the input which decreases distortion at the expense of reduced amplifier gain.In sound, we encounter a different type of feedback which is based on the same principle- it is most commonly exhibited as the high-pitched oscillation or ringing as the acoustic sound from a loudspeaker is picked up by an open microphone, and returned back to the loudspeaker via the system electronics, creating a feedback loop. If this state is allowed to occur untouched, oscillation at various frequencies, dictated by the environment, system, and system components, occurs. There are very many ways to alleviate the possibility of feedback, such as proper equipment choice, equipment position, equalization, and a careful operator.Sound system electronics are also prone to feedback; for instance, if one should happen to patch a console output back into a console input, the electronic sound signal is effectively in an electronic feedback loop, and will cause similar oscillation at frequencies dictated by the components in the electronic system. This process was used in early analog synthesizers to produce specific sounds.

Filter - An electronic circuit that passes AC signals of some frequencies and attenuates others, designed originally by the telecommunications industry to compensate for signal loss over long distances. A true filter attenuates only and provides no gain increase at any frequency. An active filter incorporates amplifier circuitry, which allows the frequency to be boosted or cut. Filters set to different frequencies, when combined, create equalizers.For information on how a filter works, consult your Electrical Engineering text.

Flange or Flanging - Flanging is the audible effect created by mixing an audio signal with a time-delayed copy, in which the time delay is modulated by an external source. The effect is that of a sweeping comb filter, as frequencies over the entire frequency spectrum are boosted and cut at will due to phase differences at different frequencies.Flanging was originally created by using two reel-to-reel tape recorders playing the same program. The flange, incidentally, is the metal reel on which the tape of a reel-to-reel tape machine resides. Playing back both machines simultaneously, and then applying physical pressure to the flange of one machine briefly slowed down the program of one machine with respect to the other. This time delay produced audible phase-shift in the resultant summed signal. As the reels on both machines were alternately slowed-down, this achieved a modulated time delay between the two signals which produced "whooshing" comb-filtering results. Electronic devices were soon developed that emulated the physical process.Compare with Phaser.
Flat - Jokes about young girls aside, an audio term used to describe an even frequency response, so called because a visual graph of frequency response that is even looks flat, with no peaks or valleys. A microphone with a flat response, for instance, has no presence peak in the high frequencies and is preferred for testing purposes.

Fletcher-Munson Curves - Two researchers at Bell Laboratories, one named Fletcher, the other Munson, were the first to accurately measure and plot a set of graphical curves illustrating the way in which the human ear responds to frequency and loudness. The curves show the ear to be most sensitive to sounds between 3kHz and 4kHz; thus, in order for sounds above and below this range to be perceived just as loud, they actually must be louder. The graphical plots that Fletcher and Munson devised are thus referred to as "Equal-Loudness Contours."

Floating Unbalanced Line - A type of output stage in which unbalanced lines are constructed to alleviate potential problems from induced noise and to trick the input stage into thinking it has a quasi-balanced input. From an unbalanced line to a balanced input, a resistor is wired to the "+", or positive, side of the signal, and the shield of the unbalanced connector is wired through a similar resistor to the "-", or negative side of the input. The shield of the balanced input is left unwired, or "floating." The input stage then thinks its see a balanced line. It is an effective workaround, but balanced lines should be used wherever possible.
FOH - Abbrev. f. "Front-of-House." The location in an auditorium or theatre that is opposite the stage, typically the mixing position for live shows. It is worthy to note that theatrical mix positions are usually at the rear of the house; front-of-house is generally more of a spiritual location than a physical location.

Foldback - A system of loudspeakers designed to provide the talent on stage or in the pit with what they need to hear, independent of the main house system. In rock-and-roll applications, foldback speakers are usually wedge-shaped and sit on the floor facing the talent or are hung from the sides of the stage aimed towards the stage. Rock-and-roll foldback usually contains rhythm and pitch information as well as a given performer's instrument or voice so that he or she can hear him or herself. In theatrical applications, foldback speakers are also found on the sides of the stage, and sometimes in the stage or built into the set, and usually only have rhythm and pitch information.
Formant - Formants are described as the inherent resonant characteristics of an acoustic sound source-- frequency bands that are emphasized due to physical construction. Instruments as well as the human voice have fixed sets of formants which dictate the timbre of the instrument or voice, and allows us to identify different instruments playing the same pitch or different humans saying the same word.
Frammel - An esoteric sound term referring to a strip of wood placed between loudspeaker cabinets when two or more loudspeakers are arranged in an array in order to separate them or angle them to reduce phase interference between cabinets.

Free Field - A loudspeaker or other sound source operating in an environment in which there are no reflective surfaces around the source. Technically speaking, there is no such thing as a true free field-- if a loudspeaker was in a free field, how would you hear it? Any time there is a reflective surface (a tree, a field hockey team, or a person), the response of the loudspeaker is being changed, however infinitesimally.

Frequency - Defined as the number of times something occurs per unit of time, given a repetitive occurence. In the sound world, we measure the number of sound vibrations per second, and give the result in cycles-per-second, or Hertz (Hz). The frequency is directly related to pitch and inversely related to wavelength.

Frequency Response - Frequency response is defined as the range between high and low frequencies that a component of an audio system can adequately handle, transmit, or receive, given a range, such as +/- 3dB. It is usually calculated by plotting frequencies versus amplitude; the frequency at which the amplitude drops by 3 dB becomes the limit of the frequency response. A loudspeaker, for example, may provide a specification of frequency response from 47Hz to 18,000Hz. Manufacturers of microphones and loudspeakers usually provide a graphical chart of frequency versus amplitude to properly judge the transducer's response at all audible frequencies.
Frequency Shifters - A processing device which is intended to increase the amount of sound system gain before feedback by shifting the output signal by a given amount, such as 5 Hz; in this fashion, a frequency of 100Hz that is prone to feedback would be fed back into the shifter and changed to 105Hz, and then would reenter the shifter to be shifted to 110Hz, ad nauseam. Very rarely used.

Frequency-Agile - Usually describes radio-frequency microphone systems which are able to operate on a selection of predetermined frequencies, usually within a preset bandwidth. Such systems are preferred for touring use, and in situations located in high-RF locations, such as New York City, because users are able to switch frequencies with the push of a button. Can also apply to radio-intercom systems.
Full Duplex - A communications term referring to simultaneous, two-way communication in both directions. Also called "full duplex." Compare with "half-duplex." Also refers to computer sound cards; full duplex audio cards are able to record and playback simultaneously.
Full Normal - A patchbay term often referred to as simply, "normal." Full-normalled jacks are wired such that the top row of jacks are automatically connected to the lower row of jacks with no patch cables inserted in the patch bay. If a cable is plugged into either jack, the connection between the two jacks is disabled, and the signal appears through the cable.
Function Generator - An audio signal generator that outputs a specific waveform (or "function") at a desired frequency. Used in testing and calibration of audio components in conjunction with a dual-trace oscilliscope.

Fundamental, Harmonics - The fundamental is the initial frequency of the root pitch comprising a sound. In physics, the fundamental is defined as the lowest pitch of a sound, and in most cases this is true in music and audio-- but not always. It is generally the loudest pitch we hear.Most sounds are composed of a combination of this fundamental pitch and various integral multiples, called "overtones," or "harmonics." The addition of different overtones to the fundamental in different amounts is what provides the sound with its own basic timbre, and enables us to discern a cello playing an A 440 versus a flute playing the same note.


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Gain - Defined as the amount an electronic circuit amplifies a signal.Also refers to a physical knob on the input channel of a mixing desk which controls the amount of amplification the preamplifier section provides to the rest of the input. Do not confuse with "fader," which controls the amount of signal, having already been preamplified, delivered to the output section of the mixing desk.

Gain Structure - Refers to the interconnection of many components of audio equipment are used together in a system, and how much amplification (increase in audio signal level) or attenuation (decrease in audio signal level) is done by what components. It is important to maintain good gain structure in an audio system in order to properly use the components in a fashion consistent with their design, which results in optimal dynamic range and signal-to-noise ratio throughout the system. The key to proper gain structure is to ensure that no one component is disproportionately amplifying or attenuating the audio signal, unless it is specifically designed to serve that purpose. An example of bad gain structure is a system in which a mixing desk's main outputs are turned as high as possible, while all of the input faders are near the bottom of their travel, and the gain on each input is turned up as much as possible. While this will output audio, the chances for distortion are huge. A correctly set gain structure would use only as much gain as is necessary at the input, set the faders at a comfortable, near-midpoint level, set the master faders at a near-midpoint level, and adjust other equipment accordingly.

Gain-before-Feedback - A term given to the amount of headroom a sound reinforcement system or subsystem has before the output level becomes great enough to introduce feedback. Theoretically, this value can be calculated and measured in dB, but is more commonly a "state of being".

Gate - A signal processing device, based on the structure of an Expander, which, instead of simply using downward expansion to push an input signal that falls below a threshold further, it drops the signal almost entirely to a predetermined level. Gates are often used in the recording of drums to prevent other drums from bleeding into a microphone, and are extensively in "Automatic Microphone Mixers," which mute unused microphones by judging whether the sound that the microphone is receiving is simply ambient noise (quiet) or a person (loud). Can be thought of as a piece of equipment that has zero output until the input signal is detected to be over a preset threshold.Also "noise gate."
GHz - Abbrev. f. "Gigahertz," one-billion (1,000,000,000) cycles per second. European mobile telephones operate at 900MHz and 1.8GHz; U.S. digital mobile telephones operate at 1.9GHz; Japanese mobile telephones operate at 1.5GHz. New cordless telephone systems operate at 2.4GHz.
Gooseneck - A wonderful invention! A flexible metal tube that is used in sound to attach a microphone to a stand. The gooseneck is flexible enough to allow the microphone to be directed freely, but is rigid enough that it allows the microphone to stay in that position. The metal gooseneck can generate annoying sqeaky sounds in microphones, and manufacturers have developed synthetic compounds which do essentially the same thing.What I want to know is, WHO exactly invented the gooseneck, and WHEN?!Anyone who can answer that for me correctly will get... oh, I don't know, their name mentioned here.

Graphic Equalizer - An audio signal processing device used to modify the frequency response of an audio signal-- an equalizer-- with slider level controls that change the relative levels of frequency bands. Sometimes preferred in rock-and-roll situations and stage-monitor situations due to the ability to "see" a graphical representation of the equalization curve based on the slider position at a glance. Other engineers prefer parametric equalizers, which have variable knobs for frequency, bandwidth, and boost/cut, making them somewhat more flexible in proper system equalization.
Grazing Effect - Sound- the way in which sound is absorbed by the audience; raking or stepping the seating area reduces the absorption and improves sight lines.

Ground - In electrical engineering, a conductor connected between a piece of electrical equipment and the earth (the planet), which is used as a zero-reference of electrical potential. Also refers to the zero-reference itself. To "ground" something describes the process by which a piece of equipment is connected to ground, and is provided as a safety feature. If the piece of equipment should fail and a situation in which the equipment operator may be subject to full voltage potential should arise, the electrical voltage travels through the ground conductor and into the earth, safely circumventing the operator.In audio, it is important to follow good grounding schemes: never defeat the third grounding pin on audio equipment, and ensure that all receptacles and cables are wired properly. One central ground reference point should be used; this is usually located at the main power distribution center; when more than one ground reference appears in an interconnected system, a ground loop results, which usually leads to hum or other assorted interference in the audio system.

Ground Lift - A process used to eliminate ground loops (usually present in the form of hum) in systems whereby one or more of the grounds in the system is disconnected ("lifted"). The process can be executed via an in-line adaptor which disconnects pin one of the XLR connector, or via a switch found on many pieces of audio equipment, which disconnects the audio signal ground from the chassis ground. The highly unsafe and heartily not recommended method to lift a ground is by cutting or otherwise disabling the grounding pin on the AC cord. This is a highly dangerous way to eliminate ground loops. Avoid it at all costs.

Ground Loop - A state of a video, audio, or other system, in which too many grounds of different pieces of equipment are connected at too many different points. Variances in ground potential between different pieces of equipment create a voltage difference running along the grounds of the equipment which results in a mains frequency hum in the system. This hum will manifest itself at 60 Hz (in the US; 50 Hz in Europe) and its various harmonics.The easiest way to alleviate potential (ha ha) ground loop problems is by ensuring that all audio equipment (including electronic musical instruments, video equipment, and intercom) are connected to ground at one point, using a centralized power distribution source. Audio ground-lifting, often an option on direct boxes and some mixing desk input channels, is also a popular method to disconnect the audio shield between pieces of equipment. AC ground lifts, which remove the third grounding pin from the AC connection, should be avoided whenever possible; disabling the grounding pin from the AC connection can result in a potentially hazardous situation. Don't do it whenever possible.
Group - See Subgroup.
Group Delay - An intrinsic characteristic of electronic components that causes different frequencies to be delayed by different amounts; usually low frequencies will be delayed slightly longer than high and mid frequencies. Although the introduced delay is negligible, some engineers find that manipulating the component designs can improve sound quality.


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not done yet!


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IATSE - The International Alliance of Theatrical Stage Employees. The international (USA and Canada) bargaining unit (Union) for stagehands, such as property masters, electricians, carpenters, riggers, wardrobe mistresses, and audio engineers.
IEC - Abbrev. f. "International Engineering Consortium," a European organization dedicated to standardization and organization within the electronics industry. Probably their most famous innovation is the IEC power cable, that ubiquitous square-ish removeable power cable seen on computer products and sound equipment.

Imaging - In studio recording, imaging refers to the ability to localize (or place) a specific sound within the stereo field, either as it applies to the human ability to place a specific instrument within the mix, or as it applies to the loudspeaker system in a given room and its ability to accurately represent the stereo image.In sound reinforcement, imaging refers to the human ability to localize a sound source. In most sound reinforcement system designs, the goal is to provide the illusion that the sound appears from the performers themselves, who are usually onstage. With careful loudspeaker placement and even more careful system delay and equalization, the listener can be fooled into thinking the sound originates at the stage, instead of from loudspeaker systems. Can also apply to the ability to localize a sound effect.

Impedance - Refers to the resistance of a circuit or device to alternating current. While resistance is measured in reference to direct current, because of the sinusoidal nature of the AC current, resistance is coupled with the complex reactance (learn your imaginary numbers, kids!) to provide the impedance. All things being equal, more electrical power, measured in watts, will flow through an electrical circuit with a low impedance than through a circuit with a high impedance. However, if the impedance is too low, some electrical components, such as amplifiers, are not able to provide the voltage and current necessary to drive such loads. It is abbreviated by the Greek letter Omega (½), and measured in Ohms. In electrical equations, resistance is signified by "Z." In addition, impedance can be defined as the ratio of voltage to current.

In-Phase - A state of audio/electrical nirvana in which all alternating current waveforms (such as an audio signal) are on the same half of the positive/negative waveform. For example, an audio signal chain is said to be "in phase" when a positive pressure on a microphone produces a positive audio waveform which passes through a mixing desk with a positive audio waveform, and is thus bussed to a loudspeaker which produces a positive pressure. Can also be termed "Absolute Phase" or "Absolute Polarity." The term can also apply to adjacent microphones and their need to be the same polarity with respect to each other, or to adjacent loudspeakers and their need to be the same polarity with respect to each other. Two in-phase loudspeakers, barring positional constraints, that are fed the same audio signal will produce a constructive waveform which will be cumulatively louder in amplitude than if only one speaker was operational. Conversely, if two loudspeakers are wired with one wired 180¡ out-of-phase with respect to the other, the two waveforms will destructively interfere, and, barring positional constraints, the two waveforms would cancel out.
Inductance - Production or storage of electrical current across or within a space from electrical or magnetic fields. The electrical component which is capable of doing this is called an inductor, which has a specific magnetic field strength, and which is capable of storing electrical energy.
Inductor - A device that stores energy by creating a magnetic field, usually within a coil of wire.

Infrasonic - A term given to sounds or audio signals whose frequencies are below the normal human hearing range (usually considered to be 20 Hz). Compare with "subsonic," commonly used- erroneously- to mean infrasonic.
Input Channel - The section of a mixing desk which receives and processes the signal from an external source, such as a microphone or CD player. Mixing desks may have anywhere from one to hundreds of input channels.

Insert, Insert Chain - An audio circuit in which an external processing device, such as a compressor or noise gate, is added to the input signal chain within an input channel of the mixing desk. In practical terms, an audio signal is sent out of the input channel post-pre-amplifier to an external device, whose output is then routed back into the input channel for post-processing (equalization on the input channel) and level controls (auxiliary feeds, master fader). Some applications include inserting a compressor on the input of a bass guitar, or inserting an equalizer on a subgroup.
Intermodulation Distortion (IM or IMD) - A measurement of audio equipment designed to calculate the products of distortion produced by nonlinearities in the unit that cause distortion that is not harmonically related to the original waveform. In English, the measurement quantifies harmonic distortion that is not a function of the original signal; instead it is a measurement of the distortion introduced into the signal by the equipment and/or circuitry itself.

Intermodulation Distortion (IMD) - A type of distortion, falling into the "undesirable altering of the audio waveform" category, created by the interaction of two or more frequencies in an audio signal that results in the generation of new frequencies, not present in the original audio signal. These new frequencies are equal to the sum and difference of the frequencies of the original signals, and subsequent multiples thereof. In addition to finding intermodulation in loudspeaker design, the same principle applies to similar phenomena found in radio frequency coordination, of interest when using many RF microphones in a heavily rf-populated area. The common multiples that are checked when coordinating radio frequencies are the third-order and fifth-order multiples.
Intonation - Literally, the word means "pitch," or the use of pitch. In musical terms, intonation often refers to pitch accuracy; ofttimes the word is used in such context as, "That violin's intonation is off," which translates into, "the instrument is not in tune with itself." In vocal terms, human beings use pitch variations to help convey meaning or emotion.

Inverse Square Law - Pertains to any physical condition in which the magnitude of a physical quantity follows an inverse relationship to the square of the distance-- i.e. doubling the distance quarters the quantity in question. Sound pressure waves follow this scheme, and in a free field, doubling the distance results in a 6dB decrease.

Isolation Transformer - In audio, an isolation transformer is a transformer (coils of wire electrically isolated) which allows audio signals to pass from input to output with no direct electrical connection. Similar to a lighting opto-splitter, this adaptor can relieve grounding problems which usually exhibit themselves as hum or buzz in the system. The term can also apply to an electrical power situation, in which three-phase power (five wire: neutral and ground) is fed into one side of a large electrical transformer, and the output is tapped from the opposite end of the transformer. In this way, electricity is allowed to pass without any extraneous noise that may be present in the feeder line. A transformer split is a set of microphone inputs that incorporate a small audio transformer at every input and split the signal in two ways: one is a direct parallel connection, and one is an output from the transformer. Many rock-and-roll and some theatre sound packages utilize a transformer split system when a monitor desk is used in addition to a front-of-house desk. The front-of-house desk, usually responsible for supplying the phantom power to condenser microphone, will be connected to the direct output of the transformer split, while the monitor desk will be connected to the transformer split side, obviating the need for the monitor desk to provide phantom power, and eliminating any potential grounding problems.


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Jack - Term for the terminating point of a circuit. Usually refers to a female connector, and even more specifically to a female 1/4" connector.
Jackfield - Often used as an alternate for patchbay, the jackfield is a single row of female connectors on a patch panel or patchbay.

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Comments, Questions, and Additions should be addressed via e-mail to Kai Harada. Not responsible for typographical errors. - © 2001 Kai Harada, 07.12.2001