B&H Glossary of Terms - Pro Audio

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Pro Audio Glossary of Terms




A standard compensation used in measuring audio specifications whereby the result is modified to account for the human ear's sensitivity to certain frequencies. A-weighting usually returns a slightly better result than non A-weighted measurements, but to be meaningful, comparisons between products need to done using either one standard or the other, but not both.

A/D Converter

An Analog to Digital Converter (ADC) is an electronic device whose function is to convert signals from the analog domain (vocals, instruments, and stereo sources) into digital data. The data can then be recorded and manipulated within a computer audio workstation or stand alone digital recorder. The converters can be either built-in or standalone. The quality of these devices can vary substantially.
(See Jitter)

ADAT Optical

A form of data transfer developed by Alesis for use in their ADAT machines. Using light as the carrier signal, ADAT optical is similar to TosLink two channel formula and uses a similar connector, but is optimized to include up to eight discreet channels of digital audio. Used today as one of several digital transmission protocols for linking digital audio devices.
(See Light Pipe)


The Audio Engineering Society (AES) is a professional body that sets standards for the audio community.


Refers to one of the digital signal protocols used to transfer data from one digital device to another. Usually implemented physically using 3-pin XLR connectors and 110-ohm cabling.


Automatic Gain Control (AGC) is a circuit that automatically adjusts the level of incoming audio so as to optimize the record level of the receiving device. Mostly employed in low cost audio and video recorders to avoid the complication of manual adjustment.


Audio Interchange File Format (AIFF) is a file format for storing digital audio data. It supports a variety of bit resolutions, sample rates and channels of audio. The format has been embraced by the Apple platforms, but is also widely used in professional programs that process digital audio data.


Audio Stream Input/Output is a cross-platform, multi-channel protocol for audio transfer that was developed by Steinberg and is now being adapted by many manufactures of audio/MIDI sequencing applications. It allows various programs to communicate with different sound cards and to recognize all of the inputs and outputs available on the sound card. The user can then assign these I/O ports as needed for recording or playback when using an ASIO-compatible software program.


In acoustics, the property exhibited by certain materials to absorb (as opposed to reflect) sound waves. Used by studio designers to control the sound energy in a given space. Also used in reference to the conversion of sound or radio frequency (RF) energy into heat.

Absorption Loss

In wireless microphone applications, the loss that occurs when a transmitted signal passes through a material that absorbs a portion of the RF energy, reducing the signal level available to the receiver.

Access Time

The time it takes from when a disc access command is issued until the read/write head reaches the data sector requested. Access time is important in data intensive situations like hard disk recording, multimedia playback, and digital video applications. Lower access times are better.


A circuit or device that uses transistors, integrated circuits or vacuum tubes to perform an action on an electrical source. Typically these systems require power to operate and are often used in amplifiers or active equalizers. The down side to using active components is the probability that noise and distortion will be introduced into the signal. Also refers to a type of speaker that has integrated amplification within
the same enclosure as the speaker elements.

Active Splitter

An electronic device that consists of a Radio Frequency (RF) signal splitter, preceded by an RF amplifier that compensates for the RF loss of the splitter. Used to allow one antenna to feed several receivers.

Adjacent Channel Rejection

The ability of a radio receiver to reject interference from an undesired signal on another nearby channel frequency. In wireless applications, unless the frequency separation between the desired signal and the adjacent signal is specified, the term is generally not of any practical significance.


MIDI data that is transmitted by a digital keyboard after a key has been struck and additional pressure is subsequently exerted on the key while it is being held down. Most often routed to control vibrato or volume, Aftertouch comes in two flavors, Channel (or Mono) being the most common implementation. Polyphonic Aftertouch allows for multiple keys to transmit individual amounts of modulation data simultaneously, but few keyboards offer this functionality today.
(See MIDI)


A procedure or formula for solving a problem. In FM synthesis the term refers to the various sound producing structures employed. Also used in effects processors, particularly reverb, to artificially simulate acoustic spaces and other effects.


In digital sampling and recording, aliasing is a digital distortion that occurs when the program material being sampled contains frequencies higher than one-half the selected sample rate (called the Nyquist Theorem). Most digital recording devices have filters that remove these frequencies that would otherwise cause aliasing to occur.
(See Nyquist Theorem)


Also referred to as amps, amperage is a measure of electrical current. An ampere is the unit of measure for the rate of electron or current flow past a certain point and in a given amount of time, through an electrical conductor.


An amplifier is an electronic device that increases the voltage, current or power of a signal. Used in wireless communication, broadcasting and in audio equipment, they can be categorized as either weak-signal amplifiers or power amplifiers. Weak-signal amplifiers are used primarily in wireless receivers, acoustic pickups, audio tape players and compact disc players. Power amplifiers are used in wireless transmitters, broadcast transmitters and for sound reinforcement.


A conductive physical device designed to radiate RF energy from a transmitter, or to capture RF energy for a receiver.

Antenna Diversity

A form of diversity that uses three receiving antennas. The three signals are combined into a single composite output that is applied to a non-diversity receiver. No longer used by any major manufacturer due to unpredictable and generally poor performance.

Antenna Splitter

An electronic device that consists of a radio frequency signal splitter (power divider) preceded by an RF amplifier that compensates for the RF loss of the splitter. Used to allow one antenna to feed several receivers.


A device for electronically creating a series of notes from a synthesizer. Rather than playing held notes simultaneously, the arpeggiator plays the notes in series. On some synthesizers this may be a simple iteration of the held notes in ascending or descending order, while on other synthesizers, very complex algorithms are employed to trigger notes in seemingly random and sometimes outrageous manners.


Attenuation is a general term that refers to any reduction in the strength of a signal, whether digital or analog. It is a natural consequence of signal transmission over long cable runs, or it may be purposely achieved with circuits to prevent overload and distortion in an audio signal path.

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BNC Connector

A type of small "twist and lock" RF connector often used with coaxial cables and antennas in wireless systems. Also used in audio and video to carry clock signals. A BNC male connector has a pin that connects to the primary conducting wire and then is locked in place with an outer ring that turns into a locked position.


Abbreviation for Beat Per Minute, a standard way to define tempo, often used in electronic music and sequencing software.

Balanced Circuit

A signal-carrying circuit that employs two conductors, each of which carries the same signal potential but with the polarity of one reversed with respect to the other. Any noise that is induced into the circuit will be common to both "legs" and on arrival at the destination, is cancelled out by combining the out of phase signals. Applies equally to balanced lines. Balanced connectors are generally 3-pin XLR or TRS 1/4" phono.

Banana Plug

A connector that is designed primarily for connecting speaker wire to the binding posts on the back of power amplifiers.


A range of frequencies, as defined by a regulatory authority or by commonly accepted usage. In audio, the term usually refers to equalizers, in particular graphic EQ's. In telecommunication, a frequency band is a specific range of frequencies in the radio spectrum. Used in wireless microphones.

Bandpass Filter

An electronic device or circuit that allows signals between two specific frequencies to pass, but that attenuates signals at other frequencies. Bandpass filters that have amplifiers for boosting the levels of signals in the accepted frequency range are known as active filters. Devices that do not amplify and consume no power in doing their task are referred to as passive filters.


Technically the term refers to the width of the range of frequencies that any digital or analog signal occupies on a given transmission medium. Audio bandwidth is generally given as 20 Hz to 20kHz, although there are harmonic components in audio that extend far above the 20k point. Generally, when presented as a specification, the wider the frequency response the better. However, in practice this can be misleading, since there is no uniform method or point in a signal chain that manufacturers must adhere to when making this measurement.


Used to describe patch bays or cables based on the Western Electric/AT&T long frame switchboard. Sometimes referred to as TT bays. Liked by professional installations because of the large number of points that are available for a given size patch bay.


A display device indicating a value, usually by means of a row of LED's or LCD segments. One or more LED's or LCD segments illuminate to display the present value of the function being monitored. Bargraphs have replaced fragile and expensive mechanical meters for most low-cost audio equipment.

Barrier Strip

Also know as a terminal strip. A series of screw terminals arranged in a line, to which other devices are connected. Popular on equipment from about twenty years ago due its low cost and reliability, nowadays the connectors are mostly found on amplifiers or crossovers that are going to be installed into permanent installations.

Bias Voltage

A low DC voltage typically supplied by a body-pack wireless transmitter to power a condenser microphone. Not to be confused with phantom power.

Binding Post

Type of output connector on a power amplifier, or as the connector on a speaker cabinet. A very versatile connector, accepting banana plugs, alligator clips, and bare wire. Usually color-coded.

Bit Depth

In digital audio, the term is used to define the number of bits a digital device uses to process audio. While sampling frequency determines the outer frequency limits that a piece of hardware is capable of processing, bit depth refers to the dynamic range that can be captured during recording. The number of possible "levels" that can be recorded at 16-bit is 65,536, while this figure jumps to 16,777,216 using 24-bit hardware. The human ear is very sensitive to these levels, and given properly implemented converter designs, 24-bit recordings will sound more "open" than 16-bit recordings. However, it is also true that a top of the line 16-bit converter could sound better than a very poorly implemented 24-bit converter. Although bits and sampling frequencies are important specifications, the kinds of filters used, and the integrity of the audio path prior to the converters is also very important as to how a particular converter will sound.
(See Floating Point)

Black Burst

Also referred to as house or video sync. Derived from video editing where video decks and cameras needed to proceed from one frame to other with absolute synchronization, the term is now finding use amongst audio professionals as they find the need for their digital workstations to lock to picture when working on film or video projects. A black burst generator simply outputs a video signal with no picture content. All the equipment that need synchronization is connected to this generator, and since they are all receiving the same clock signal, they remain locked to each other. Not to be confused with SMPTE time code, which is used for positional reference.
(See Clock, SMPTE Time Code)

Boundary Microphone

A type of microphone that detects sound pressure level changes at a boundary of the acoustic space in order to reduce interference between direct and reflected sound.


Generally an unwanted side effect of using compressors in an incorrect manner, whereby the background noise of the source material rises and falls depending on the behavior of the main program. Also referred to as pumping.

Brickwall Filter

A type of filter in which the cut-off slope is very steep, almost resembling a wall. Sometimes used in converters to remove source material above the Nyquist frequency, but the negative results of phasing and attenuation of bands near the center frequency make them unusable for higher end applications.

Broadcast Wave File

A subset of the standard .wav audio file format commonly used by PC's. The specification restricts what kind of audio data can be carried, along with extra data that provides information on the title, date, time etc. of the audio file. It's most important function for digital audio is the provision for time stamping which allows users to move individual files from program to program and have the ability to "spot" the file to it's original position.

Bulk Dump/Load

A feature of MIDI devices that allows the transfer of specific data between devices. Bulk dump/load was of ten used to back up MIDI data via System Exclusive messages, and is still used for that purpose today by lower cost hardware.

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Cable Loss

The inherent loss of coaxial RF cables due to conductor resistances, absorptive losses in the insulating material and signal leakage between the braids of the outer shield.


The portion of a microphone that converts acoustic energy to electrical energy. Often includes shock mounts, acoustic isolators, protective covers and electronic circuitry in addition to the basic transducer. Also called an element.


A microphones pickup characteristic, notably strong sensitivity to material presented to the front of the microphone, while sensitivity falls off from sources arriving at an angle of 90° or greater away from the front, and good rejection from the rear. The name derives from a representation of the polar pattern, which loosely resembles a heart shape. Prone to exhibit pronounced proximity effect, where bass frequencies are accentuated the closer the source to the microphone.
(See Hypercardioid)


A modulated RF signal. That is, one which is carrying audio or other information. FM and AM radio employ two carrier signals but modify them in different ways. FM synthesis uses a carrier as part of the algorithm for generating sound. The carrier usually outputs the original sound source and is subsequently modified by other operators to change the timbre and other characteristics of the sound.

Center Frequency

The particular frequency to which a given filter-band in an equalizer is tuned to. Parametric equalizers are able to sweep the center frequency, providing a greater degree of flexibility to the EQ, while graphic EQ's have a number of fixed center frequencies. The amount of boost/cut that can be applied to the center frequency will also affect adjacent bands to a greater or lesser degree, based on the "width" or Q that is set on the filter.


In wireless, a designated radio frequency available for use by the transmitter and receiver. In audio, the circuit path for a signal, or a functional unit that is designed to independently process a signal.


Used in reference to headphones and means "around the ear." Can be combined with semi open, closed and open back designs.
(See Supra-Aural)


Clipping occurs in analog and digital audio circuits when the incoming signal exceeds what a particular device can accommodate. Visually, it results in the flattening of the signal peaks, as if the waveform had been "clipped" off. In certain analog circuits light clipping can have a positive effect, producing a pleasing distortion. In digital circuits the general rule is that clipping is to be avoided at all costs, since it produces a nasty and harsh sound.

Class A

A type of amplifier design where the output device is always on for both parts of a complete sinusoidal cycle. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot, due to the amplifier constantly operating at full power. The positive effect is that class A designs are inherently the most linear, producing the least amount of distortion and are thus often found in high-end audio equipment.

Class B

Class B is opposite to class A in that the current in a specific output flows for one half cycle. In other words, both output devices are never on simultaneously. This system allows for much better efficiency, but displays poor linearity around the crossover region, since it takes time to turn one device off and the other device on. This in turn translates into extreme crossover distortion, thus restricting class B designs to power consumption critical (battery operated) applications, such as two-way radio and other communications audio.

Class AB

A class AB amplifier is a combination of both class A and B in that the output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the non-linearity of class B designs is eliminated, without the inefficiencies of the class A design.

Class H

If an amplifier has more than one voltage rail then it is designated Class H. Its operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. For most musical program material the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. If fact the input signal actually modulates the higher supply voltage. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. Using multiple power supplies improves efficiency enough to allow significantly more power for a given size and weight.


In digital audio or video, a clock serves as a timing source. Data has to be executed at very specific times for digital audio or video to function properly. An issue that has to be addressed when synchronizing systems with each other. Although audio and video require different references to keep data passing through a system correctly, they both do it with the aid of a clock. This could be black burst, word clock, or clock embedded in a digital data stream, such as AES/EBU or S/PDIF.
(See Black Burst)

Clock Speed

In a computer, clock speed refers to the number of pulses generated by an oscillator that sets the tempo for the processor. The faster the processor can access data, the faster the computer can perform its functions, given that other parts of the system are sufficiently tuned to support the particular clock speed. Clock speed is determined by a quartz-crystal circuit, similar to that used in radio communication equipment, and is measured in megahertz (MHz)or even gigahertz (GHz.)

Closed Back

In reference to headphones, describes the design of the cup where there is no venting of the audio to the outside. Closed back, circumaural headphone are often used in studios, where "bleed" from the headphone can be picked up by the recording microphone. Closed back headphones minimize this problem.

Coaxial Cable

Called coaxial because the cable includes one physical channel that carries the signal, surrounded by another concentric channel, both running along the same axis, but separated by insulation. They are used for high frequency transmission of telephone, television and audio signals. Coaxial cable was invented in 1929 and first used commercially in 1941. For audio, different types of cabling are required for analog as opposed to digital transmission.


The function accomplished with an audio compressor. A circuit is employed to reduce gain by a variable amount when the output begins to exceed the preset threshold. In wireless microphones, the process of reducing the dynamic range of the audio signal by a factor of 2:1 via a logarithmic compressor for transmission.


A circuit that performs compression of an audio signal. By setting the ratio and threshold controls, the user is able to tame large dynamic swings. For instance, a 2:1 ratio means that if the program material rises by two decibels, the output will only rise by one decibel, once the threshold setting has been exceeded. There are many uses for compressor, from controlling the large dynamics of live performances, increasing the overall level of a signal, increasing the sustain on a guitar or just evening out a performance. Other controls such as attack and release times will further modify the source material.
(See Limiter)

Condenser Microphone

Type of microphone in which the capsule consists of conductive diaphragm next to a backplate. The entire assembly is given an electric charge, (often via phantom power) which basically creates a capacitor out of the capsule. Sound waves hitting the diaphragm cause it to move in relation to the backplate, producing a variation in the capacitance of the capsule. This in turn produces a variance in the output voltage, which can then be turned back into acoustic energy.
(See Electret Condenser Microphone, Phantom Power)

Confidence Monitoring

Listening directly from the recording medium while recording is in progress, thus ensuring the source material is being recorded correctly. Used in high-end analog recorders and DAT machines, a secondary head reads the recorded material immediately behind the record head. This allows the user to monitor the actual recording to detect any errors, and therefore one can say that the recording is done with full confidence.

Contact Microphone

A contact microphone receives its entire signal from being in contact with a particular surface and the resulting mechanical vibrations, not from airborne sound waves. Sometimes referred to as piezo or transducer microphones.

Control Surface

Available in many sizes and levels of complexity, control surfaces are used to control the functions of some other device, often a computer software program. Particularly in computer based audio recording and mixing, a control surface can replace the tiresome use of the computer mouse, and provides a physical connection with many or all of the parameters in a given piece of software. Additionally some control surfaces can provide additional features that are usually found on dedicated consoles, such as talkback facilities.


Refers to the built-in audio capabilities of the Mac OS X. Similar to Sound Manager found in earlier Apple OS, CoreAudio deals with the way audio is handled within the computer and any application that is written specifically written to support it. Two of the major advantages that CoreAudio has over Sound Manager are support for multi-channel audio and the ability to specify exact outputs on connected hardware, and the inclusion of high sample and bit rates. Although still in its early days, Apple's move to provide these features as part of the OS will speed the rise of "native" applications, and perhaps bring a seismic shift to computer audio production.


Similar to CoreAudio, the term refers to the built-in MIDI support embedded in Apple's OS X.


An electrical device that divides the audio spectrum of a particular source into smaller groups of frequencies, making it easier for down stream components to handle the load. The most common use of crossovers is in amplifier/speaker systems, which allows the separate components to function more efficiently. For instance, a mid-range speaker will function better if it does not have to deal with low frequency content, and visa versa.


In wireless microphones and digital devices, a frequency stabilizing device consisting of a small quartz crystal in a holder. The quartz naturally vibrates and the frequency can be made highly stable by external circuitry. This in turn is used to establish the operating frequency of wireless transmitters, receivers and other RF and digital equipment.

Crystal Controlled

In wireless, equipment whose operating frequency is directly established by a crystal, rather than indirectly as in a frequency synthesizer. Also commonly used to refer to equipment that is only able to operate on one fixed frequency, as versus a number of synthesized frequencies.

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Digidesign Audio Engine is the underlying code that allows Digidesign software communicate with computer platforms and operating systems. DAE is required for third party software to access Digidesign hardware. Prior to HD systems, DAE was an actual separate application. For HD systems, DAE is now integrated into the Pro Tools application.


Digital Audio Tape. A two track 16-bit digital recording and playback system.


Digital Audio Workstation. Usually refers to a computer with audio recording, playback and editing features. Nowadays, entire projects can be completed on DAW.

D/A Converter

Digital to Analog converter. The opposite of an A/D converter where audio signals in the form of digital data are reconstructed back into an analog waveform. As with ADCs, DACs come in a variety of configurations and prices ranges, and vary in how faithfully the program material is reassembled.
(See Jitter)


The decibel (abbreviated dB) is a unit used to measure the intensity of a sound. However, the dB scale is not linear, rather it is a unit used to express the relative levels of two electrical voltages, powers or sounds. It is never an absolute value.


Also sometimes referred to as dBv, it is dB referenced to voltage. 0dB equals 0.775 volts.


dBV also references voltage, but does so without regard for impedance. 0dB equals 1 volt. The dBV rating is most commonly found in reference to consumer equipment that uses operating levels of -10 dBV.

DC Offset

An imbalance that can sometimes occur at an A/D converter, where DC (direct current) which is basically a constant voltage, is introduced into the digitized signal. Apart from reducing headroom, DC content can introduce clicks and pops while the audio is being edited.


A recordable DVD disc. Not to be confused with DVD-RAM and DVD-RW, both of which are rewritable mediums. DVD-R is a write once, read many medium which currently holds about 4.7 gigabytes of information.


A type of DVD media that is designed for storage and backup. No other equipment other than the drive itself is required for a user to use DVD-RAM. In fact, DVD-RAM discs act very much like hard drives, other than being a much slower medium, in that a user can simple drag and drop files on to the desktop icon.

Damping Factor

In reference to power amplifiers, the damping specification is the ability of the amplifier to control speaker motion once signal has stopped. The effects of damping are most apparent at low frequencies - an amplifier with a high damping factor will make a speaker sound "tighter" in the low end, while low damping factors result in indistinct bass.


Device for reducing the effect of sibilance in vocal signals. Basically, a de-esser is a frequency dependent compressor, although these days such devices are very sophisticated and optimized in the way they tackle the problem of sibilance.


Physical click stop in a control knob/switch such as a pan or EQ cut/boost knob.


The portion of a microphone that is mechanically moved by sound waves. The resulting interaction with a backplate or moving coil (depending on the microphone type) allows the conversion of sound energy to electrical energy. This energy eventually gets to a loudspeaker or headphone, where a roughly equivalent reverse process takes place as the cone moves in response to the electrical signal and produces sound energy.


A type of antenna with two defined opposing radiating elements, both of the proper length for the frequency of operation, and each forming a counterpoise for the other.

Direct Box

Often abbreviated as DI (short for Direct Inject) used primarily as a device for matching the impedance of a source to the inputs of a tape machine or mixer. Typically, the output of a bass or electric guitar is a high impedance, unbalanced signal, that needs to be converted into a low impedance balanced signal, either for long cable runs to a live console, or for imputing into a recording device. The process also allows the electronics on these instruments to function at their correct levels, thus often improving the sound.


The property of transmitting /receiving energy more strongly from/to certain directions, than others.


A method of "burning" a CD, disc-at-once writes to the disc in one pass - the laser in the CD burner never turns off, even in silent passages. Required by mass duplicators of Red Book audio CDs. Although CDs written track-at-once will generally play in consumer CD players, the duplicators at mass manufacturers will reject such a disc as fatally flawed.


A term that has taken on a specific meaning, but which is in fact much broader in its definition. Technically, distortion is any change in the shape of an audio waveform compared between two points in a signal chain. Therefore adding EQ and compression also adds distortion to the original signal. But generally the term refers to the desirable or undesirable "breaking-up" of audio (as in distorted guitars.)


A method of reception providing protection from signal loss due to multi-path nulls, which are localized small areas with a very low RF signal level caused by multi-path propagation.


The taking of a audio file with a high sample rate, and sample rate converting down to a lower sample rate. Used in particular when a project is recorded at a high sample rate and the audio files need to be prepared for CD distribution.


In wireless microphones, a loss of RF signal, which in turn results in loss of audio or audio that is noticeably noisy. Also refers to a small physical area where there is insufficient RF signal present to obtain satisfactory wireless operation. Dropouts are normally caused by multi-path or signal blockage due to some type of obstruction. Also refers to areas on oxide tape where there is a problem with the coating and where subsequently audio or digital data is not properly reproduced.


Piece of software that handles communications between the main program and a hardware peripheral, such as a soundcard, printer or scanner. Drivers are constantly being updated due to OS rewrites and the like.


Refers to a type of multi-pin connector that is commonly used for computer connectivity, although in last few years manufactures such as Tascam and Digidesign use the D-Subminiature connector for supplying multi-channel audio to and from their systems.


A system for controlling the level of one audio signal with another. For example, background music can be made to "duck" whenever there is the need to hear a voice over.

Dynamic Microphone

A type of microphone that consists of a diaphragm connected to a coil that operates in a magnetic field. Any movement of the diaphragm due to sound pressure levels moves the coil within the magnet, thus producing an electric current. Dynamic microphones do not require external power to operate, are generally more robust, and therefore favored for live use (although several manufactures are making condenser microphones specifically for live use.) The downside is that due to their construction, dynamic microphones are less sensitive to fast transients and don't have the high frequency response of the condenser variety.

Dynamic Range

The range in dB between the noise floor of a device and its defined maximum output level. The term applies to both audio devices and RF equipment.

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Acronym for Enhanced Audio Streaming Interface developed by Emagic, and is designed to standardize communication between audio software and hardware. The standard is cross-platform and is similar to ASIO, developed by Steinberg, but differs from ASIO in that Emagic has made EASI totally public, with no need to sign non-disclosure agreements.


EIN is a specification that is mostly relevant to microphones and preamplifiers. It stands for Equivalent Input Noise and deals with the self noise that is a feature of virtually every piece of electronics. Since microphones output a low-level signal, any noise present will be boosted proportionately. The specification is usually measured with a 200ohm source resistance, which on its own produces a level of noise that when referenced to a line level signal is equal to -129.6dBu of noise. This is theoretically the lowest noise level that can be obtained, but some manufactures play with this figure a little by measuring their equipment with lower source impedance.

Early Reflections

The initial sound reflections from walls, floor and ceiling, created when an acoustic event happens in an acoustically reflective environment. Often a parameter that can be adjusted in units that electronically simulate acoustic spaces (reverb processors.)

Electret Condenser Microphone

As the name implies, a variation on a condenser microphone, but with a permanently charged plate in the capsule. This negates having to supply external power to the microphone.
(See Condenser Microphone)


In wireless microphones, the radiation of an RF signal, whether intentional or not.


Originally design to add back some of the high-frequency content lost in audio production due to multiple passes using analog tape. Techniques used include dynamic equalization, phase shifting and harmonic generation.

Envelope Generator

All sounds can be described in a variety of ways. One of them is the manner in which a sound evolves amplitude-wise, starting from silence to full volume to final decay. Or how the harmonic content changes over time. In synthesizers, these changes to an oscillator or filter are achieved using envelope generators. EG have various break points supplied to help adjust the rates and levels of the various parts of the envelope.


Hardware device or computer plug-in used to alter the frequency balance of an audio source. An equalizer has the ability to boost or cut specific frequency ranges based around a center frequency and can be used either creatively, to drastically alter a source, or in a corrective manner, such as in a mastering situation, to even out anomalies in a mix. Equalizers come in various forms, including parametric and graphic, active or passive.
(See Filter, Graphic, Parametric)

Expander Module

Synthesizer with no keyboard, often rack mountable or in some other compact form. Useful for users who already have a keyboard and do want another one, but want the sounds offered.


In wireless microphones, the process of restoring the original dynamic range of the audio signal by means of a 1:2 logarithmic expander.

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Field-Effect Transistor typically used as an impedance converter at the element in a condenser microphone. A MOSFET is a particular kind of FET, which is finding itself used more and more in power amplifiers.


In acoustics, the undesirable leakage of audio from loudspeakers, back into the same microphone which is being used for originally capturing the audio. If too much feedback occurs, the system can go into self-oscillation, causing unpleasant howling or squealing. In electronics, such as power amplifiers, feedback can be used to achieve specific results, such as performing input/output comparisons.

Feedback Eliminator

An automatic electronic device that senses the onset of feedback, and cancels it before it gets out of hand. This is achieved by using a specialized equalizer with multiple, very narrow filter bands, positioned between the audio source and the speakers. The unit "searches" for the beginnings of feedback, analyzes the problem frequency and cuts that band. Good eliminators carry out this whole process in mere milliseconds, and can respond to the fact that feedback may occur at many different frequencies throughout a live performance.


A microphone polar pattern whereby the capsule is most sensitive to sound sources from the front and back equally, but sounds from the sides of the microphone are rejected. Sometime referred to as bi-directional. Also describes certain antenna patterns, such as that of a dipole.


An electronic circuit designed to attenuate a sound source's energy at a particular frequency. A true filter is always passive, in that it does nothing to add to the signal. However, most filters these days have amplifiers attached to them to allow the user to both boost and cut particular frequencies (active filters.) Multiple filters can be combined to create equalizers that are either passive, active or both.
(See Equalizer)


Apple computer's version of the IEEE 1394 standard, which is a high-speed data exchange protocol. FireWire provides a single plug-and-socket connection on which up to 63 devices can be hung. Additionally, the technology allows for hot-swapping devices, while data transfer allows for speeds of up to 400 Megabits per second. Common on personal computers these days, FireWire is also finding its way into consumer electronics, particularly digital video.
(See IEEE-1394)


Flanging is an audio process where two copies of the same signal are played together, with one variably delayed against the other. Originally created using two tape machines and "leaning" gently on the flange of one of the tape reels, today the effect is produced using digital effect processors. Feeding the processed signal back into the device to be processed again can deliver a more intense effect, although many are of the opinion that the original tape based method is still superior.

Floating Point

A data encoding process that allows the representation of very large numbers with fewer bits. Used in computers that have floating point registers, and where complex graphics, scientific or audio processes need to be executed rapidly. As far as audio is concerned, a debate is presently centered around whether floating point or fixed-point computation is better for the end product, in terms of sonics. So far there does not seem to be a consensus on this issue, since there are advantages and disadvantages to both systems.
(See Bit Depth)

FM Synthesis

Originally developed by John Chowning of Stanford University, and later popularized by Yamaha's FM7 synthesizer, FM synthesis is a method of sound generation where a sine wave is modulated by one or more sine waves to produced a large variety of waveforms. Later incarnations of the process used many other types of waveforms for the carrier and modulators, producing an even wider palette of sounds. Know primarily for the pure bell-like and electronic piano tones


An emphasized frequency component of an instrumental or vocal sound that does not change with pitch, and which helps to distinguishes one instrument from another, and gives voices their unique characteristic. Problems arise in the audio world where pitch shifting is common, (samplers, DAW editing) since in this case the formant characteristic is pitch-shifted along with the overall pitch of the signal, making the resulting audio file sound unnatural. Various manufactures of pitch shifting processors have tried to address this issue with a modicum of success.


The process by which data written to a hard drive is stored in small packets that may or may not be next to each other. The result of continual erasing and saving from/to the hard drive, severe fragmentation can cause a slowdown in drive performance with drive intensive applications like digital audio, since the head mechanism has to constantly jump around to read all the data.


In audio the indication of how many cycles of a repetitive waveform occurs during one second. A waveform which repeats once per each second has a frequency of 1Hz (Hertz.) Frequency also references to human hearing as pitch.

Frequency Response

A measurement of the frequency range that can be handled by a specific piece of electrical equipment or loudspeaker when referenced to amplitude. A graph of all the frequencies plotted versus level is the Frequency Response Curve of a particular piece of equipment.

Frequency Stability

In wireless applications, the accuracy to which the operating frequency is maintained over time and in the presence of environmental changes.

Frequency Synthesizer

A circuit to generate a stable and precise RF output on any one of a number of preset (or programmable) frequencies. Synthesizers are used as the local oscillators for receivers, and to set the output frequency of transmitters.

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An extension to the General MIDI protocol developed by Roland for use in its own synthesizers.


The extent to which a circuit amplifies a signal. Usually part of an amplifier specification, its value is most often expressed in a decibel value.

Gain Before Feedback

The amount of total gain that can be achieved in an audio system, from microphone to speakers, before the onset of acoustic feedback.


A dynamic device that has the ability to stop audio passing through it based on a certain threshold. Originally designed to shut down audio output in passages with no program material (where tape hiss might be evident) or to lower bleed on drum microphones. Gates can also been used creatively, notably the gated reverb of Phil Collins' 80s drum sound.

General MIDI

An addition to the original MIDI specification that allows for consistent playback on any instrument that is GM compatible. Achieved by requiring that groups of sounds have very specific locations (a piano sound on one synthesizer will have the same location on another,) that all instruments have 24-voice polyphony, and that certain continuous controllers are similarly defined. In theory, music sequenced for General MIDI should play back on any other GM instruments with the similar type of sound on the same MIDI track with any volume and pan information also being executed as written.
(See MIDI)


A flexible metal coupling that is used to attach a microphone to a stand or podium. Used mostly in conferencing and for podium mounting, the metal spiral allows the microphone to be adjusted into a multitude of positions.

Graphic Equalizer

The term nowadays refers to a type of equalizer where 15 or more, narrow frequency bands are controlled using sliders, either boosting or cutting the individual bands. The term graphic came about because the arrangement of the sliders provides a visual representation of the EQ curve. Graphic equalizers can still be found that use rotary controls instead of faders.

Ground Effect

The loss of operating distance due to the positioning of wireless antennas too close to the ground. Reflected RF energy from the ground gets mixed in with the direct RF signal and causes cancellation of RF energy at the antenna. In certain situations the loss can be significant. UHF systems are less susceptible to this effect than are systems that use VHF, due to the shorter wavelength of the former.

Ground Lift Switch

A switch found on some equipment that disconnects the shield of a balanced cable from the local equipment ground. Used in situations where ground loops are problem.

Ground Loop

A condition where current circulates in the ground wiring system, due either to the grounds at the end of a length of cable being at different AC potential, or where a video or audio system has multiple paths to ground. Manifests itself usually by varying levels of hum (in audio systems) or as rolling bars in the picture of a video system. One way to deal with it is to use ground lift switches, but generally it is better to find the offending piece of equipment and then checking it to find out why it is causing the ground hum.

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Hammer Action

In search of the ultimate "piano-feel keyboard" synthesizer manufacturers have often employed weights on the back-end of individual keys to simulate the action of real pianos. However, to really achieve a similar feel, certain manufacturers have resorted to installing hammers on the end of the keys, which when the key is struck, moves the hammer to strike a surface. The resulting feel is much closer to that of a piano's actual playing action.

Handheld Transmitter

A wireless microphone transmitter consisting of both the microphone and the transmitter electronics in one integrated package.

Handling Noise

Refers to the sensitivity that a microphone exhibits to movement, the actual holding of the microphone and shock. A microphone's ability to lower handling noise is a direct result of the construction of the microphone, and to that end, some manufactures employ internal shock mounts for the capsules to eliminate as much handling noise as possible.

Hard Disc

A high capacity computer storage device that is based on a rotating rigid disk with a magnetic coating onto which data may be recorded. The hard disc drive should technically refer only to the mechanism that controls the positioning, reading, and writing of the hard disc, but today hard disc, disc drive etc. are terms that are commonly used for the combination of the two parts.
(See IDEbzwfdzxsquzebafaqyyytauaftczrbzzyafaa, SCSI, Seek Time)


A harmonic is a wave whose frequency bears a whole number relationship to the frequency of a reference signal. Complex sounds, such as the human voice or the sound of a stringed instrument always consist of a fundamental frequency and then a number of harmonics, which, depending on their amplitude, will make up the basic characteristic of that sound. So the second harmonic is always two times the fundamental, and so on through the rest of the harmonic series. Discordant sounds have several or many harmonic waveforms that do not bear the whole integer relationship present in the basic sound.

Harmonic Distortion

The result of passing audio through some electronic device. Since it is impossible to make a perfectly linear device (audio out exactly matches audio in) harmonic distortion is always a byproduct of signal processing. The amount of distortion a particular piece of electronics creates is in most cases kept as low as possible, particularly in reference to "transparent" microphone preamplifiers. However, sometimes the "coloring" is acceptable and indeed favored, and can be taken to extremes.


The difference expressed in dB between the nominal operating level of a device, and the maximum level that can pass through the device without being distorted.

Headworn Microphone

A small microphone mounted on a short boom and held in place close to the performer's mouth by a headband or similar device. Used by performers who need their hands free during dance numbers or to play an instrument.

Helical Antenna

A type of antenna formed by a coiled small-diameter spring, usually covered in plastic and somewhat flexible. Physically shorter than a standard 1/4-wavelength whip antenna, but also considerably less efficient.


A unit of frequency, named after Heinrich Hertz, a 19th century German physicist. So if a complete single cycle of a waveform occurs over 1 second, the waveform is said to have a frequency of 1Hz.

High Pass Filter

A filter that attenuates frequencies below a certain cutoff point, while passing on frequencies above the cutoff unaffected. Sometimes referred to as low-cut filter.
(See Filter)

Host Based

Used in reference to computer based recording systems. In the early days of computer recording, much of the processing work had to be done on additional hardware cards, while the computer merely provided visual feedback. But because of the unprecedented power that is available in today's computers, it is entirely possible to have a virtual studio within the computer, using only the computers processing power. Host based systems are still hampered to some degree when compared to their hardware card equivalents, but as computer power increases, so host based systems become more and more economical.

HRS Connector

A type of audio connector often used for the microphone connections on wireless body-pack transmitters. The connector wiring is not standardized within the wireless industry. Also referred to as a Hirose Connector


A type of microphone pick-up pattern. Similar in shape to a cardioid pattern, except that the sides have the greatest amount of rejection, as opposed to a cardioid pattern where the rear of the microphone has the least sensitivity.
(See Cardioid)

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Integrated Drive Electronics is a standard electronic interface that is used as a data path for a computer's disc storage devices. IDE drives are cheaper and less expensive to implement when compared with SCSI drives. And whereas SCSI drives have traditionally been viewed as more robust and quicker than the IDE counterparts, the gap between them is shrinking due to the general reliability of hard drives in general. Apple suspended the use of the SCSI interface in their computers several years ago, and now provides the cheaper EIDE bus, which is an enhanced version of IDE.
(See SCSI)


A high-speed data exchange protocol, it provides a single plug-and-socket connection on which up to 63 devices can be hung. Additionally, the technology allows for hot-swapping devices, while data transfer allows for speeds of up to 400 Megabits per second. Common on personal computers these days, IEEE 1394 is implemented by Apple as FireWire, and by Sony as iLINK.
(See Firewire)


Intermediate Frequency. Wireless receivers normally convert the incoming RF signal to a lower intermediate frequency for amplification and final filtering prior to demodulation.


Abbreviation for input/output. In audio, the term refers to the physical inputs/outputs of a particular piece of equipment. Also used to describe any operation, program or device that transfers data to and from a computer.

Image Frequency

In receivers, the process of converting the desired RF frequency results in an undesired sensitivity at a second RF frequency, which is referred to as the image frequency. RF filtering in the receiver is relied upon to reduce to acceptable levels the receiver's susceptibility to spurious RF signals at the image frequency.

Image Rejection

The measure of a receiver's ability to reject signals at its image frequency. Normally expressed as the ratio, in dB, of the receiver's sensitivity at the desired frequency versus the sensitivity at the image frequency.


An expression of the opposition that an electronic component, circuit or system offers to AC or DC current. Impedance contains both resistive and reactive components, although generally only the resistive part of the circuit is usually quote in specifications as Ohms. So the higher the resistance, the higher the impedance.


To restore a piece of equipment to its factory default settings.

Insert Point

A connector at a particular point of a circuit that allows for the introduction of a piece of external equipment, so that the original signal now flows and is processed by the external equipment prior to being returned back into the original circuit.

Intercept Point

A measure of the inter-modulation performance of a RF devices. Devices with high intercept points will generate lower levels of undesirable inter-modulation products as compared to similar devices with lower intercept points.


A device that acts as an intermediary to two or more pieces of equipment. An audio interface for a computer allows signals generated by a preamplifier for example, to be communicated to the computer software. The software itself is also an interface, but in this instance it is between the operator and the computer itself.


A process that can result in distortion. Inter-modulation is the result of two or more frequencies inter-reacting with themselves and generating new frequencies that are not present in the original signal. These are invariably based on the sum and difference of the original frequencies.


The process in IT (information technology) that requires near exact timing coordination to successfully transmit information, such as video or audio data. Isochronous data transfer ensures that data flows continuously and at a steady rate so that the receiving mechanism can display the result without interruption.


An isotropic radiator is a transducer that produces useful electromagnetic field output in all directions with equal intensity, and at 100% efficiency. In wireless applications the isotropic radiator is theoretical, although the dipole antenna roughly approximates it. It is used as a standard reference source against which the performance of other antennas is measured.

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Jam Sync

Jam Sync is a setting that is selectable when using a synchronization device with SMPTE time code. It allows the receiving synchronizer to regenerate time code if there are errors or drop outs in the original code. If jam sync is not used, then a drop out will cause the slave device to go off line.
(See SMPTE Time Code)


Jitter is the deviation of some aspect of the pulses in a digital signal. In audio applications, Analog to Digital converters are one of the most critical components that are susceptible to jitter. Using an internal or external clock, an A/D converter "slices" an incoming audio signal into a number of pulses that digitally conforms to the original source. These pulses have to occur and proceed with very strict timing, and any periodic displacement of the signal from its ideal location will cause jitter. Jitter can be caused by the converter having a poor clock, or when source impedance is incorrectly matched at the load. The results are heard as low level distortion or noise, and since high frequencies are more susceptible to jitter, a loss of high end definition. The issue is that once jitter has been introduced into the digital data it is impossible to remove it.
(See A/D Converter, D/A Converter)

Jog Wheel

A physical controller that allows a tape machine's transport to move tape back and forth a small distance to find an edit point. Originally used by video editors to find an exact location on tape, jog wheels can be found on audio control surfaces to provide similar functionality within a digital audio editor.


Gamers have traditionally used joysticks for controlling games. It is a device that allows control of two different axes simultaneously. Certain synthesizer manufacturers have utilized the principle instead of using separate modulation and pitch wheels, but the main usage of the device is now beginning to appear in surround sound production. Pan pots are two- dimensional devices (left/right,) and since surround sound requires at least four points to define an audio source location (left/right/front and left/right/rear,) joysticks are a common feature on surround consoles and control surfaces.

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The kilohertz is a unit of alternating current or electromagnetic wave frequency equal to one thousand hertz. The unit is used in measurements of bandwidth, but in audio can also refer to the pitch of a particular tone.


Term is used in reference to a synthesizer or sampler that uses sample data for the raw building blocks of the sound generation. It is a means to assign each sample to a particular key or range of keys. So a piano keymap would theoretically have each tone from the entire piano keyboard mapped to exactly the same keys on the synthesizer or sampler. A second keymap might contain similar information, except that each note was sampled using a stronger/lighter strike of the piano keys. Of course, it is not always necessary to assign one sample per key. In fact one could assign a single sample across the entire keymap. Different manufactures refer to keymaps by other names, such as Key Group or multi-sample.

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Liquid Crystal Display. A technology used for displays in notebook and other small computers, all the way to advanced VGA computer screens. It is also found on lower cost electronic music devices. LCD's are generally manufactured utilizing a single crystal plate and a specific pattern of electrodes. Applying voltage between the electrodes changes the phase of the light travelling through, or reflected by the material, thus altering the information displayed.


Light Emitting Diode. A semiconductor device that emits light when an electric current passes through it. Used for status lights or bar graph meters in many audio devices, LED's are also found everywhere from watches to laser disc players. Some LED's emit infra red energy and are found in remote control devices and wireless headphone systems.


Low Frequency Oscillator. An oscillator that is designed primarily to operate below the threshold of human hearing (though not exclusively) and to provide modulation function. Often found in synthesizers and effect devices. For instance, vibrato, a cyclic variation of pitch is generated by modulating the audible portion of the signal with an LFO which, depending on its pitch of the LFO, will create a slower or faster vibrato.


Latency is an issue that can be found in several areas of audio production. In its broadest sense it means the delay that increases response time beyond the time desired. For instance, in a MIDI keyboard instrument, there is a slight delay, or latency, between when a key is struck and when the actual sound is produced. In computer based recording systems that use native processing, a delay exists between an audio event being imputed, and when the same event arrives at the monitoring stage. The delay will increase if the computer has to deal with any real-time processing. To avoid the discomfort that is experienced by this delay, many systems employ input-only monitoring during overdubbing.

Lavalier Microphone

A type of miniature microphone that is usually worn fastened to clothing or hung around the neck. Designed for situations where a microphone would be obtrusive, such as film sets or TV talk shows, the microphone is typically made with a steep high pass filter to reduce noise generated from the microphone moving against clothing. Also know as a clip-on or lapel microphone.

Light Pipe

An optical cable. The term was originally coined by Alesis to differentiate between their 8-channel protocol and the 2-channel optical connectors found on CD players and DAT recorders. The actual fiber optic cable used is the same in both cases, only the form of the transmission is different.
(See ADAT Optical)


Similar in principle to a compressor, a limiter is an audio processor that prevents the amplitude of an audio signal from rising above a certain threshold, regardless of what is happening to the amplitude of the source audio. Dynamics below the threshold are more or less unaffected. Certain compressors can in fact function as limiters if their ratio can be set to infinity:1. Uses for limiters include maximizing levels for CD release, optimizing recording levels for imputing into a DAW or when going to tape, or to protect users of in-ear monitors from sudden volume surges.
(See Compressor)

Line Level

Although the term refers to the average level of a signal, these days use of the term is more specific and applies to the two line level references, balanced and unbalanced. Balanced or professional equipment operates at +4dBm or 1.23 volts, while unbalanced or semi-professional equipment operates at -10dBV or 0.32 volts. Although the distinction between professional and semi professional equipment is blurring, the important fact is that the two levels should not be speaking to each over. If two pieces of equipment need to be connected that use different line levels, then matching transformers need to be used. Otherwise the +4dBm signal will overdrive an -10dBV input and equally a -10dBV signal will not deliver enough level to a +4dBm input.


Seigfried Linkwitz, a Hewlett Packard engineer along with a co-worker Russ Riley, authored a paper in 1976, in which they described a new form of crossover, which improved vastly on the standard that existed at the time. Nowadays, many crossover designs in the sound reinforcement community utilize the Linkwitz-Riley filters.
(See Filter)

Local On/Off

A function of an electronic keyboard, that allows the use of the keyboard and the sound generating section to be used independently of each other. Using a MIDI router, it is possible to control the sounds of remote devices without triggering additional sounds from the sound source of the triggering synthesizer.
(See MIDI)

Lowpass Filter

A filter that attenuates frequencies above a certain cutoff point, while passing on frequencies below the cutoff unaffected. Sometimes referred to as high-cut filter.
(See Filter)

Low Impedance

A loosely defined audio term used to describe devices whose input or output impedance is less than approximately 5,000 Ohms. For microphones, Lo-Z commonly is 50 - 1,000 Ohms.

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MOTU Audio System is a plug-in engine developed by Mark of the Unicorn for use in its software. Plug-in engines developed by competing manufacturers do not support MAS. However, by using an extension called VST Wrapper, Performer is able to utilize VST plug-ins.


Modular Digital Multitrack. A digital recorder that can be used in conjunction with other similar format machines to provide a greater number of tracks than a single machine. Originally pioneered by Alesis with the ADAT format and Tascam with their DA series, machines that conform to these standards can be synchronized in a more transparent manner with up to 128 tracks acting like a single machine.


Musical Instrument Digital Interface. Originally developed in the early 1980s to control one digital synthesizer from another, today MIDI is used to transmit almost every aspect of a musical performance. However, it must be understood that MIDI data is all about how a sound will be produced, not the actual sound itself. So data sent from one device to another could find itself being played with a piano sound while the original information was actually a drum sequence. General MIDI was in part introduced to alleviate this problem, except that the subset was really a consumer format and of not much use to the professional community. Amongst the command sets of MIDI are note-on, note-off, key velocity and pitch, modulation such as pitch bend, program changes, timing and many more. Its use has moved outside of strictly music and is used for lighting cues amongst other applications. The one great advantage of MIDI, apart from its ubiquity, is that file sizes are relatively small compared to what an actual audio file would be. The MIDI protocol uses eight-bit serial transmission with one start bit and one stop bit, has a 31.25 KBPS data rate, and is asynchronous. Connection is made through a five-pin DIN plug, of which only three of the pins are generally used.
(See General MIDI)

MIDI Interface/Patch Bay

A means of distributing multiple independent MIDI streams usually based around a sequencing station. The original MIDI specification allowed for 16 discreet channels of information to flow through a single cable. With the arrival of multi-timbral synthesizers, a single stream of MIDI information could easily be dedicated to a single synthesizer, and any other units connected to the same source would also be forced to play the same information. By connecting a MIDI interface to a computer, most sequencing software is able to create multiple MIDI streams, each with 16 discreet channels of information that can then be routed to multiple sound sources. Along with MIDI patch bays, which are generally free standing, these devices are often capable of more than just distributing the MIDI streams, including the ability to filter messages, transpose certain channels and lots more.


Synchronization systems available to MIDI users that include MIDI Clock and MIDI Time Code.


A MIDI connector found on electronic synthesizers, that passes through untouched the MIDI data that is received by the MIDI input.

MIDI Time Code

A form of time code that is based around real time. Like SMPTE time code, the units of measure are hours, minutes, seconds, frames and subframes, but sent as part of the MIDI stream.
(See SMPTE Time Code)

MIDI Time Stamping

A term coined by MOTU to denote a method of coding MIDI data to allow the computer to re-trigger this information with grater accuracy. Before time stamping, MIDI transmission suffered from a certain amount of "slop" due to a sequencer program having to rely on the host computer's clock to manage timing issue. But with the advent of USB MIDI interfaces and time stamping, this is no longer an issue.


The MOSFET is a particular type of Field-Effect Transistor (FET) where the output current flowing between the source and drain terminals is controlled by a variable electric field applied to the gate terminal. The gate design determines the type of FET. In the MOSFET, the gate is insulated from the channel by a very thin (typically less than the wavelength of light) layer of glass. This means the MOSFET has practically infinite impedance, which makes it useful for power amplifiers. They can also be found in some integrated circuits (IC) and often used in wireless microphone receivers.
(See FET)


MPEG-1 Audio Layer 3 is a standard established by the Moving Picture Experts Group for compressing audio files. Using perceptual coding, file sizes are reduced by a factor of 12, without too much damage to the sound quality of the original file. Indeed, some argue that because of the way data is discarded, there is no perceptible difference in sound quality between an MP3 and the original sound file. However, most audio professional would disagree. The format is used extensively throughout the Internet, both legally for demonstration purposes, and of course illegally, as in the recent Napster controversy.

Mic Level

The level of a signal generated by a microphone. Generally ranging between 0.001 to 0.005 volts, to make it useful for recording, the signal requires a microphone preamplifier to bring the signal up to line level.


Often refers to the middle part of the audio frequency spectrum, as perceived by humans. For example, a midrange driver would be a speaker that was optimized for that particular range.


A format introduced several years ago by Sony that allows recording and playback of audio to and from a small magneto optical disc with a capacity of 140MB. To be able to record 74 minutes of music, the technology applies a data compression algorithm called ATRAC that compresses the data by about 5:1, but also permanently changes the file on decompression. Therefore it is know as "lossy" algorithm. However, the advantages are a very compact size, a claim of 1,000,000 reuses of the media and the ability to random access data on the disc.


A miniature phone plug, available in both mono and stereo versions. The most common size for audio use is 3.5 mm (1/8".)

Mini-XLR Connector

A Switchcraft Tini-QG connector, frequently called a mini-XLR, is available in several configurations. The connector is often used on small boundary microphones, and for the microphone connections on some wireless body-pack transmitters. The pins are numbered in the opposite direction from a standard XLR but the wiring scheme is not standardized within the microphone industry.


A device for summing two or more electrical signals. In general audio usage, a device to process and sum the outputs of two or more microphones or line level sources


Modulation is the addition of a control signal to an electronic or optical signal carrier. In electronic synthesis, one example might be the sine wave output of a low frequency generator (LFO) being added to a pitched note produces vibrato. Another form of synthesis uses the principle of frequency modulation (FM) to generate a whole range of sounds, by modulating the frequency of an audible frequency with the frequency of another signal. AM and FM radio both employ modulation to broadcast their signals.


In audio applications, the term is synonymous with a reference loudspeaker that is used for recording and mixing. They come in various shapes, sizes, configurations and can be passive (requiring an amplifier) or powered (built-in amplifiers.)

Mono Bridge

A feature provided on two channel power amplifiers that allows the two channels to be combined to produced a single channel output to a speaker than would otherwise be possible from either channel alone. Usually engaged by a dedicated switch.

Moving Fader Automation

A type of mixing automation that uses small motors to control the physical faders, which may or may not be used in addition to VCA. On high priced consoles and control surfaces these are generally touch sensitive, requiring only the placement of a fingertip on the fader to commence updating the automation information. The advantage of moving faders is that the fader is always at it's correct position at any given moment, thus giving visual feedback to the engineer of each channel's status. Additionally, many engineers prefer the use of faders without the additional use of VCA's since in their opinion, the inclusion of these components can degrade audio quality.


In wireless microphones, generally refers to a transmitter or receiver that has more than one user-selectable operating frequency.


An electronic device that consists of a RF signal splitter preceded by a RF amplifier that compensates for the inherent RF loss of the splitter. Allows for feeding several receivers from one antenna.


Radio frequency signals arriving at a location via different transmission paths, usually from a combination of direct and reflected signals. The direct and reflected signals are often opposite in phase, which can result in a significant signal loss. The problem is most apparent indoors and in areas where many metallic surfaces are present.

Multipath Null

A small area or space where direct and reflected RF signals from a transmitter cancel each other, resulting in little or no usable energy being available to a receiver antenna.


Refers to a type of microphone where the polar pattern of the capsule can be changed, either using a switch a changing out the capsule.


An electronic synthesizer or sampler that is capable of playing back multiple parts simultaneously, each under the control of a different MIDI channel. Not to be confused with polyphony, which refers to total number of simultaneous notes (or voices) that is available to the whole instrument.
(See MIDI)

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In reference to digital audio and computers, the term means software that uses the processing power of the computer, and does not require additional hardware. Also sometimes referred to as host based. However, plug-in architectures that are written for native systems are not technically native themselves, since they require the presence of other software to actually function.

Near Field

Although not technically correct, the term near field is generally applied to a loudspeaker system that is designed to be close to the monitoring position. In this way the listener receives more of the direct sound from the speakers, while minimizing the effect of sound produced by reflections from walls, floors and ceilings.


A rare-earth metal element that can be made into magnets, amongst other things. However, it is its properties for making stronger magnets than other materials of the same size that make the element of interest to the audio community. Used in microphones, it can produce greater output than non neodymium versions, for headphones it allows for lighter drivers and for speaker design it allows for more powerful drivers for a given size.


The Nickel Cadmium is a type of rechargeable battery that is used in electronic equipment. Although they have an even power discharge, they provide less operating time than corresponding alkaline batteries.

Noise Floor

The amount of self-noise generated by a piece of electrical equipment when it is at rest (no signal passing through.) All such devices generate noise to some extent or another, and engineers are constantly striving to lower this artifact. Measured in decibels.

Noise Reduction

A range of technique developed for reducing the amount of noise in an audio signal. Dolby NR is an example of a system designed to reduce the amount of tape noise that is inherent in the analog tape medium.

Noise Shaping

A system developed to compensate for the quantization errors that are introduced into digital audio files when reducing the bit rate of the data, such as when preparing audio for CD duplication. A certain amount of noise is added to the audio data, which helps to smooth the errors. In which part of the audio spectrum this noise resides varies from one developer to another.

Noise Squelch

A squelch detection technique that monitors noise at the FM demodulator output, at frequencies above the audio range. A high level of noise in this region indicates a weak or unusable RF signal, or some form of interference.
(See Squelch)


A standard single-channel RF receiver.

Nyquist Theorem

A principle used by engineers when designing equipment for the digitization of analog signals. Due to the complex nature of sampling audio, the theory states that for any given sample rate, the maximum bandwidth of the analog source must fall below one half the sampling frequency. If this formula is not followed, errors in the form of aliasing will be introduced into the data file. To prevent this happening, analog to digital converter usually have steep filters to remove any material above the Nyquist frequency.

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Apple Computers latest incarnation of their operating system, described as being the first complete revision. Apart from the fact that Apple maintains that the OS will make future revisions easier, for audio two features stand out. Memory protection that prevents a "crashed" application from bring down the whole computer, and the addition of core audio, where functions of audio production that were previously taken care of by applications are now part of the operating system.


Term used to describe the position of a sound source in reference to the microphone recording the source. Generally, a microphone will record best when the source is directly in front of it, but since moving the microphone off-axis results in coloration of the signal, engineers sometimes use it to good effect.


Although used to describe the temporary condition of not being connected to a network, for audio and video purposes the term refers to the processing of files that is not done in real time. Often it is because the computational device is not fast enough to perform the operation while the source is playing. In postproduction, the act of non-linear editing is also considered off-line.


Unit of electrical resistance. Named after its founder Georg Ohm, Ohms law states that current varies in direct ratio to the wires' resistance.


Describes a device such as a microphone or antenna that operates equally well in all directions.

Open Reel

A type of tape recorder that uses tape that is wound on spools rather than inside a casing, such as a cassette or DAT tape

Optical Compressor

A type of audio processor where a light source is used as a means of controlling the amount of attenuation applied to the audio signal. A form of compression developed in the late 50's and while found mostly in high-end equipment, reissues of "vintage" opto compressors have seen a resurgence lately.

Orange Book

The name for Philips and Sony's recordable CD standard published in 1990. In addition to specifying the first recordable CD formats, the specification also deals with how the data is managed, hybrid disc and multisession operation amongst other things. With the publication of the Orange Book specification, users were able for the first time to perform desk top disc writing, a function taken for granted today.
(See Red Book)


An electronic circuit designed to generate a period electrical waveform at a particular frequency. Oscillators are found in computers, wireless receivers and transmitters, and music synthesizers. Early synthesizers used oscillators as the raw source for creating sound, using filters and envelops to shape the sounds.


A condition where the signal levels present exceed the capabilities of a device, causing an undesirable consequence, such as distortion.


Used during analog to digital and digital to analog conversion and refers to the process whereby the converters sample at much higher rates than the base frequency. This allows the filters to be much gentler in slope, which results in less phase distortion in the audible spectrum.

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Peripheral Component Interconnect, originally designed by Intel, is an interconnect system for sending data between the CPU and peripherals independently of the processor. Found on many desktop computers these days, not only those based around Intel processors, the standard allows for 32-bit transmission of up to 132Mb per second, and has found a use in such high data rate applications as digital audio and video. 64-bit PCI busses are also now available.


Personal Computer Memory Card International Association was organized in 1989 to promote standards for credit card-size devices that can fit in a portable computer. Originally designed as a storage device, it later expanded to other applications such as modems and networking. For audio and video users, the technology has been extended to include input/output devices. PCMCIA cards come in the same rectangular size, but differ in thickness according to application.


Psychoacoustically Optimized Wordlength reduction is a sonically transparent digital word length reduction algorithm, reducing 20, 24, and even 32-bits files to the CD standard 16-bit format. Pow-r is technically not noise shaping, although it performs a similar function, and aims to retaining a high degree of perceived dynamic efficiency with very low noise. The algorithm is scalable, meaning it is ready for all sample rates, even to 192kHz and beyond.


Peak Program Meter. A type of meter designed to register signal peaks rather than the average level of an electrical source.


Pulses per Quarter Note refers to the timing resolution of a MIDI sequencer. It refers to the number of subdivisions within a quarter note that a MIDI event could possibly start on. Nowadays resolutions are high enough (960 ppqn and more) that most sequencers will accurately reproduce what is played into them, compared to early sequencers that had resolutions of 96 ppqn, and sounded mechanical.
(See MIDI)


Pressure Zone Microphone. Also know as a boundary microphone. The microphone consists of electret capsule mounted to a backing plate, which is then placed on any kind of flat surface. Useful for conferences, ambient microphones or for recording piano where isolation from other sources is essential.


An electronic circuit that attenuates the output of a particular device. Often found on microphones, pads are used to bring down the microphone's output level for use with a preamplifier that would otherwise become overloaded due to a hot input.


To pan, or panning refers to the act of moving the perceived location of a sound source within a stereo soundstage. Generally works by reducing or making louder the particular sound source in either the left or right channel of a stereo output. Although slightly more sophisticated electronics are used to control this movement accurately, the net result is the same. If a source is panned hard left, then it will appear at only the left speaker, and likewise with the right side. The amounts of signal present in both speakers will determine the exact location of the sound source in between the left and right sides in the stereo field.

Parametric Equalizer

An equalizer whose filters contain controls over three parameters. Frequency and gain/cut are obvious, but the third parameter is a little more complex, and refers to a measure of the sharpness of the resonant peak. In other words, with a narrow Q, gain or cut affects fewer frequencies adjoining the center frequency, while a wide Q will affect a greater number of adjoining frequencies. Expressed as a ratio, a higher Q factor indicates a narrower bandwidth, while a lower number indicates a wider response. Thus, assuming a constant center frequency, Q is inversely proportional to bandwidth.
(See Filter, Quasi-Parametric, Q)


An electronic device that does not use any amplification circuits. Applied mostly to filters, it describes a cut-only design, and because of this, passive circuits are less prone to distortion. In practice, even though a filter is described as passive, it may none the less have make-up gain circuitry at its output to compensate for the loss in power that cutting can cause.

Passive Radiator

An element in speaker design that is used to improve the bass response of smaller cabinets. Consisting of a diaphragm that resembles a woofer, but without the voice coil, it is meant to move sympathetically with the energy delivered by the active woofer. While providing a greater bass response, the diaphragm is hard to control and can lead to overtly boomy bass response.


Also called a program, a patch refers to a single programmed sound on a synthesizer or sampler that can be recalled by a program change command. Also refers to a temporary fix for software that is publicly released, in which a bug was not previously found during the testing cycle. The patch is usually incorporated in the next software revision.

Patch Bay

A patch bay or patch panel is a means of bringing together the cabling from various pieces of equipment to a central location, thus simplifying interconnection. Developed from the days when operators manually connected two telephone callers by inserting a patch cord between two sources, patch bays today can be a little more sophisticated, allowing for more than just connecting one piece of equipment to another.


Maximum instantaneous level of a signal, peak is the maximum value, either positive or negative that a waveform achieves. Important in audio in that when a signal peaks beyond what a circuit can handle, distortion appears.

Peak Hold

The part of a non-mechanical meter, where the topmost LED will stay lit to indicate an over. Useful in digital recording or mastering situations where any overs are undesirable. Often the length of time a meter will display the over is user definable as is what constitutes an over (how many successive samples.)

Phantom Channel

A feature in surround systems that allows for the creation of center channel information when a center speaker is not part of the set-up. Achieved by folding what would be center information into the left and right speakers. This produces a "phantom" center image.

Phantom Power

DC voltage, usually 48V that is supplied to a condenser microphone using the signal cores of a balanced microphone cable. Condenser microphone need a source of power to function and nowadays most consoles and preamplifiers provide this feature.
(See Condenser Microphone)


Waveforms are repetitious. That is, they proceed through regular cycles. Phase is defined as to how far along a cycle the waveform is, with 360 degrees being the point of a completed cycle. Most engineers take phase into account while capturing an audio source with multiple microphones, since audio hitting different microphones even with a small delay, can put the summed audio out of phase, which results in certain frequencies of the original sound source being attenuated or even cancelled. In fact, if a waveform is combined with an exact copy of itself but with the two being 180 degrees out of phase, they will cancel each other out completely.

Phase Lock Loop

A phase locked loop (PLL) is an electronic circuit that has a voltage driven oscillator that is constantly adjusted to match the frequency of an input signal. Operates by comparing the phase of a sample signal, usually the frequency-divided output of the RF oscillator, with a precision fixed reference frequency. The compared phase output then drives a control loop, which forces the RF oscillator frequency to be an exact multiple of the reference frequency. Used in audio for providing low jitter clocks for WC generators and in certain analog to digital converters.
(See Jitter)

Phone Plug

A 1/4" connector found on a lot of audio equipment. The name derives from the old telephone switchboards, which used 1/4" patching cables. Generally available in two varieties, unbalanced or TS, and balanced or TRS, where T stands for tip, R for ring and S for sleeve.

Phono Plug

A type of connector originally used by RCA to connect their turntables to amplifiers. The name has stuck, and these kinds of connectors, found on consumer and semi-professional equipment are today still referred to as RCA phono connectors.

Physical Modeling

A type of synthesis that utilizes computer modeling to analyze and then describe how the physical properties of an instrument affect its tone production. This information can then be written into an algorithm that mimics the output of such an instrument.
(See Algorithm)


Derived from a Greek word that means to press, for the purposes of audio, Piezo microphones are manufactured by coupling a diaphragm to a small layer of crystal. When vibration causes the diaphragm to vibrate and therefore "push" against the crystal, a shift of electrons occurs within the crystal, thus creating a potential difference. Piezo microphones are sensitive to the source of the vibration, but insensitive to the outside world, and are useful as contact microphones or triggers for electronic drums.


Description of an audio cable that has bare ends rather than a specific type of connector. Often found on wireless microphone applications.

Pilot Tone

A specific tone frequency outside the human audio range, applied to a transmitter. Used by tone coded squelch systems for receiver squelch control.

Pitch Bend

A control message within the MIDI specification that changes the pitch of a synthesizer in response to the movement of a lever or pitch bend wheel.
Plug-In An application that runs within a parent application and adds functionality. In digital audio, plug-ins have become ubiquitous, with several manufactures providing standards for developers to write plug-ins for various platforms. These include TDM, VST, DirectX, Audiosuite and MAS and cover functions as diverse as reverb, dynamics, time based effects, EQ, limiting, dither, guitar amplifier emulation, virtual synthesizers and more.
(See MIDI)

Polar Pattern

A polar pattern is a plot of a device's sensitivity as a function of the angle around the device. Used to define the characters of microphones and antennas, the plot of the polar pattern will show how well a device will reject sounds from a certain angle (the back of a microphone) or from which angle it is most sensitive.


The ability of an instrument to play more than one note simultaneously. Technically, a piano is 88 note polyphonic, although if the human element were to be taken into consideration, then it would take 8.8 people to fully exploit all 88 notes simultaneous. Likewise, a six-string guitar has a maximum polyphony of six notes. However the term is mostly applied to digital synthesizers to specify the maximum number of voices that are available to the entire instrument. Because synthesizers are often multitimbral, not all voices need to be assigned to a single sound. In the early days of synthesis, voice allocation was often fixed or needed to be user specified. These days voicing is generally allocated in a dynamic manner.

Pop Filter

A means of shielding microphone capsules from explosive burst of air from a performer's mouth. Made from an acoustically transparent material, pop filters can either be built into the surrounding mesh of the microphone itself, or more commonly made from material stretched across a separate circular form, and attached to a microphone stand close to the microphone.


An electronic device used to amplify low-level signals. Commonly used to bring microphone outputs up to levels that subsequent equipment can utilize.


A system for applying high frequency boost to a sound before processing so as to reduce the effect of noise. In FM radio systems, noise increases rapidly in the higher audio range. To offset this, the audio signal is pre-emphasized at the transmitter, which raises the level of the higher audio frequencies relative to the lower ones. When the received audio is de-emphasized, the result yields an overall flat audio frequency response, while greatly reducing the noise introduced by the transmission process.

Pre-Fade Listen

A point in a mixer channel strip where audio is split off from the main channel is referred as an aux. This signal is normally subject to the position of the channel fader, rising and lowering along with the fader position. However fader movement could be a distraction when sending monitoring information to players (often called a cue mix.) Therefore a switch is usually incorporated at the aux that allows the split off to occur pre or post the fader, thus by-passing any fader movements. Another use for pre-fade listen is for sending a signal to a processor without the source appearing at the main mix buss. Although the main fader is lowered, signal is still flowing along the aux to the desired destination


Device designed to treat an electrical signal by changing its dynamics or frequency content. Examples of processors include compressors, gates and equalizers. In wireless, the term is sometimes referred to as companding.

Pressure-gradient Microphone

A microphone in which both sides of the diaphragm are exposed to the sound source. This means that the diaphragm is responsive to the pressure differential between both sides of the membrane.

Proximity Effect

Refers to the effect caused by a sound source being very close to a directional microphone. The net result is that low frequencies become boosted as the source comes closer. For vocalists, the effect can be used creatively, while for others the effect can cause problems, where distortion can occur from the diaphragm being stressed from the signal boost.

Pulse Code Modulation

PCM is a digital process for transmitting analog data. Using PCM, it is possible to digitize all forms of digital data including music and video. Using binary encoding, the source is sampled at a particular frequency and further quantized. At the receiving end a pulse code demodulator converts the binary numbers back into pulses having the same quantum levels as those in the modulator. These pulses are further processed to restore the original analog waveform.


An artifact introduced into audio source that is caused by excessive compression. Pumping, or breathing causes the program material to rise and fall depending on some frequency (usually bass) that is crossing the threshold level. Can be used creatively, but multiband compression or some sort of filtering to the side chain can overcome this problem.

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Refers to a measure of the sharpness of the resonant peak of an electronic circuit. One of the adjustments available in parametric equalizers. With a narrow Q, gain or cut affects fewer frequencies adjoining the center frequency, while a wide Q will affect a greater number of adjoining frequencies. Expressed as a ratio, a higher Q factor indicates a narrower bandwidth, while a lower number indicates a wider response. Thus, assuming a constant center frequency, Q is inversely proportional to bandwidth.
(See Parametric Equalizer)

Quadrature Detector

A type of FM demodulator


Refers to a type of equalizer, where control is available over frequency and gain/cut, but not bandwidth. Many mid-frequency EQ's on budget recording consoles have this kind of EQ.
(See Parametric Equalizer)

Quick Mount

Term used to describe an object with an integral output connector, which plugs into a matching connector on a receiving object. For example, a gooseneck microphone with an output connector that will plug into a matching jack.

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Redundant Array of Independent Discs. Basically a method of storing the same data in different places on multiple hard discs, thus increasing fault-tolerance. There are at least nine types of RAID arrays that cover various levels of redundancy (protection) and speeds of data access. In most cases a RAID array appears as a single disc to the operating system of a computer.

RCA Connector

A type of connector originally used by RCA to connect their turntables to amplifiers. The name has stuck, and these kinds of connectors, found on consumer and semi-professional equipment are today still referred to as RCA phono connectors.
(See S/PIDF)


Abbreviation for Radio Frequency

RF Impedance

The characteristic impedance of an antenna, cable or conductor. A value of 50 ohms is generally used for coaxial cables and RF interface points in wireless systems.

RF Line Amplifier

For wireless microphones, a RF amplifier frequently used to overcome the inherent signal losses induced by coaxial RF cables. Also known as a RF preamplifier or booster.


Real Time AudioSuite. Based on Digidesign’s AudioSuite plug-in architecture that uses off-line processing, RTAS acts exactly like a TDM plug-in, but instead of using Digidesign DSP, uses the host computers processing capability. The upside is that RTAS does not require the expensive hardware that TDM does, but the downside is that the number of instantiations will vary with processor power, and there are certain limitations as to where a plug-in can be placed.
(See TDM)


A proprietary communication protocol for Roland’s digital audio products. It allows for 8 channels of audio back and forth along with word clock and transport functions over a single cable.


Nowadays referred to as DAT and stands for Rotating Digital Audio Tape. A medium for recording digital audio, it uses similar technology to that of a VCR in which a tape passes slowly over fast rotating heads and records information in a helical scan fashion. Due to political machinations, the format never caught on as a consumer medium and was embraced for a while by the professional audio community, only to be replaced by CDR technology.

Rack Space

An industry standard measurement for equipment that is to be mounted into racks. The width must conform to 19”, while the height is specified as 1 3/4” or whole multiples thereof. For example equipment height is often specified as 3 rack spaces or 3U high. There is no specification for depth.


In wireless, the conversion of a signal in the transmitter to radio waves that can be propagated over distance.

Ratio Combining

A technique used in true diversity receivers that mixes the audio from two receiver channels in varying ratios, depending upon which channel has the stronger signal. In the more common switching approach, the receiver simply selects the audio from the stronger channel by means of an electronic switch.

Real Time

Used to describe an audio or video process that can be carried while the source material is playing or being recorded. Non linear editing is therefore an off-line process.

Red Book

Jointly developed by Sony and Philips and first published in 1980, the Red Book standard provides the specification on the optical and physical characteristics for the audio compact disc. In addition it also specifies the organization of the content, such as track numbers, table of contents etc.
(See Orange Book, Yellow Book)


In the context of signal processing and particularly dynamics, release refers the time it takes for the processing device to return to its normal state (no processing.) The term is also used to describe the final stage of an ADSR envelope, where the release portion determines how long it takes for the envelope to return to a zero position. So if the envelope generator is controlling the amplitude of a sound, the release will determine how fast a slow a sound will take to decay to silence.


The opposition that a substance offers to the flow of electric current. All electric systems display a certain amount of resistance. The standard unit of resistance is the Ohm.


Resonance is the tendency for a system or object to vibrate at a specific frequency or frequencies when excited (like a bow and violin string,) with the resonant frequency being determined by the physical parameters of the object or system. For example, when music is played at a loud volume in a space, certain features of the room may resonate to a greater extent than other aspects of the room. For instance, this in turn may cause bass buildup that would need to be removed by acoustic treatment.


Reverberation is the result of a sound source being instantiated within an acoustic environment. It usually consists of multiple primary reflections that are the result of the first interaction of the sound waves with the acoustic space, followed by more spaced out and rapidly diminishing echoes. A reverb response can be short and loud, similar to a slap-back echo produced by a highly reflective environment such as a tiled bathroom, or long and slowly fading, such as that produced inside a large cathedral. The human brain is very sensitive to this information, extracting size information very rapidly. That is why budget reverb devices sound budget, and why a good electronic reverb simulation device can cost many thousands of dollars.


Developed by Steinberg, ReWire is an inter-application communication engine for allowing one application to interact with another. For example, audio begun within a certain application can have its outputs ReWired into the inputs of another application for further processing, all without having to deal with competing audio formats.

REX File

The product of a file that has been processed within Propellerhead’s software Recycle. Audio files imported into the application are split up into smaller sections based on user-determined points and sensitivity, and the resulting file is saved with a .rex suffix. It is then much easier to pitch and time shift the original material without the usual artifacts. Other manufactures are beginning to implement the ability to import REX files into their own applications, usually into software samplers.

Ribbon Microphone

A type of microphone that uses a metal ribbon suspended close to a magnet. Any vibration in the ribbon is transmitted via the magnet and made into an electrical signal. An early design, ribbon microphones have recently seen a resurgence in popularity. Due to the physical response of the ribbon, the microphone displays a roll-off of high frequencies and therefore it is perceived as imparting a “warmer” character when recording audio into a digital device. Also has long been a favorite for recording brass and high powered operatic sopranos.

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Small Computer System Interface. A hardware interface that allows computers to talk to peripheral devices such as disc drives, CD devices and scanners. A single SCSI channel can handle up to seven unique devices each with their own address, but the last item in the chain, regardless of the number of units, must be terminated for proper operation of the SCSI chain.
(See IDE)


Sony/Philips Digital Interface is, as its name suggests, a transfer protocol for digital audio, similar in concept to AES/EBU but requiring a different electrical specification. RCA coaxial connectors are most commonly used, although TosLink optical connectors can also be found.

SMPTE Time Code

Originally used by the military for rocket launches, SMPTE time code is a standardized way of referencing the 24-hour period. Based around the video frame, the Society of Motion Picture and Television Engineers identify frames and sub frames with a unique identifier that includes hours, minutes, seconds, frames and sub frames. This way if two or more devices can read SMPTE time code, they will all have a common positional reference and keep themselves synchronized (actually both units will commence at the same positional reference, but then need to run at the same speed to stay locked. This is the function of a synchronizer.) SMPTE time code has no relationship to real time at any given moment, other than both use a 24-hour cycle. So program material that starts at hour one does not need to wait until 1 o'clock to function, but rather if a synchronized device is attached to the original device, it will also commence playback from the same hour location, unless an offset has been set in the slave device. There are various sub sets of time code that have to do with frame rates being different in film and television, but they are all still referenced to the 24-hour period.
(See Black Burst)


The process that is performed by an analog to digital converter where the instantaneous amplitude of a sound source is measured at periodic intervals, the latter being know as the sample rate. The word also refers to an audio file that has been sampled in a sampler for instance.

Sample Rate

The rate at which an analog to digital converter measures the instantaneous amplitude of a source signal. Measured in samples per second, the higher the sample rate, the higher the frequency content of the corresponding digital data. The default rate for CD production is 44.1kHz, or put another way, the source material is sampled at 44,100 times a second. Since the highest frequency that can be captured is one half the sampling rate, a CD will reproduce audio up to about 21kHz, the actual perceived range of human hearing. Arguments rage as to whether signals outside the range of human hearing have any bearing on the sounds humans do hear, and if they do, then filtering out everything above the Nyquist threshold, damages the accurate reproduction of the source.

Seek Time

Generally refers to the time taken by the head of a disc drive to access the sector where the information it has been sent to find, resides. An important specification for audio work since audio streaming is a time intensive process. Track count and edit density will dictate how much stress will be put on the drive, and therefore how low the seek time needs to be.


The measure of a receiver's ability to reject interfering signals at frequencies near the operating frequency.


In electronics all components produce some level of noise. In an electronic device or system, the total noise of all components is measured as the self-noise of the device or system. This measurement is taken into account when dealing with signal to noise ratios. The inherent noise is considered the noise floor, and the difference between that and the level of the signal is referred to as the signal to noise ratio.


Describes the construction of a headphone cup. Closed designs reject a large proportion of outside noise, but also do not "leak" sounds to the outside. Real open designs do not interfere with outside noise and obviously do little to contain the source material. Semi-open designs are a compromise between the two.


Refers the amount of signal that is needed at an input for a device to deliver its rated output. A higher sensitivity is observed when the input signal is smaller for the given output and although this is generally preferred, too much sensitivity can result in a processor being overdriven by a preceding device.


A device that triggers a series of events in a particular order. Early audio sequencers were quite primitive, used control voltage to trigger voltage controlled oscillators, but had a certain musicality to them. These days software sequencers are MIDI based and offer a high degree of sophistication.
(See MIDI)


A mechanical device that is designed to isolate the transducer of a microphone from shocks, vibrations or handling noise. Both internal and external mounts are used, but the most commonly used shockmount are external and use some kind of elastic material to suspend and isolate the microphone from the stand it is attached to. Certain flight cases are also shockmounted to prevent damage to equipment that can occur due to handling issue while in transit.

Shotgun Microphone

A type of microphone that generally has a long body with a series of holes running along the sides. The polar pattern characteristic is highly directional, with strong rejection of side and rear sources. The holes actually help in the reduction of side and rear pickup by employing a certain amount of phase cancellation at the diaphragm. Useful for picking up sounds at a distance, but also for pinpointing certain sources while ignoring much of the ambient or surrounding noise.


A high frequency component of certain vocal sounds that can cause problems while recording. Usually words that start with an "s" can produce sibilance, and some vocalists are more prone to it than others. A de-esser is a device specifically designed to dynamically correct the problem without affecting the main vocal content too much.


Also know as key input, a sidechain is a part of a circuit that splits off a portion of the main signal to derive a control signal. It can also be a secondary physical input on a processor, such as a compressor that allows control over the compressors functions according to the sidechain input. Examples are ducking and de-essing.

Signal Level Squelch

Receiver squelch (muting) that is based on RF signal strength present at the receiver input. When the RF signal is considered high enough to output audio of acceptable quality, the receiver is un-muted.
(See Squelch)

Signal Strength Indicator

A display that indicates the approximate amount of RF signal present at the input of a receiver.

Signal-to-Noise Ratio

In electrical systems SNR is a measure of the ratio of the maximum signal level relative to the self-noise of the system. Usually expressed in decibels (dB.)

Slew Rate

The measure of how fast a circuit is able to respond to fast changes in amplitude in the source signal. Although most circuits have this specification, it is most commonly associated with power amplifiers. A high slew rate will generally translate into a "tighter" and cleaner signal.

SmartMedia Card

Originally developed by Toshiba, the SmartMedia card is a memory card that uses flash memory to store data, and its size allows it to be portable among other digital devices.


For audio purposes, snake refers to a type of cabling, where multiple lines are enclosed in a larger single shield. The most common use for a snake is for live sound, where microphone leads and monitor mixes are sent back and forth between the front of house mixer and the stage. Obviously it is easier to lay a single 16 or 24 channel snake than to lay each individual line. Snakes are also used in recording studios.

Soft Knee

Describes the action of a compressor as the signal level crosses the threshold setting. A compressor functions by processing a signal above a certain threshold. Without a soft knee setting, the compressor would immediately begin processing the moment the threshold was reached. In fact this is how a hard knee setting works. But in certain circumstances this may be unmusical, so the soft knee setting allows compression to begin gradually and reach full processing only after the signal has reached a predetermined level above the threshold.
(See Compressor)

Software Synthesizer

A software application that emulates some type of hardware synthesizer. Since computer power has increased radically in the last few years, it is now feasible to have a host computer do the work previously done using hardware. Some virtual synthesizers mimic a particular vintage synthesizer, while others are more generic in nature. Modular synthesis is also supported and as computers become more and more powerful, so more and more of these virtual instruments will appear. All function in either stand-alone mode or as plug-ins.

Sound Designer II

An audio file format originally developed by Digidesign for its Sound Tools application. Although a very popular file format for the Mac, it may be finally on its way out, superceded by .aiff and .wav formats.

Sound Pressure Level

A standard measurement of the amplitude of sound, expressed as the ratio in decibels between the measured sound pressure and a standard reference.


A type of multi-pin connector developed by Neutrik and found on many power amplifiers and speakers used for PA applications. They are very durable, provide a good connection and relatively inexpensive.


In wireless microphones, a device that divides an RF signal into two or more equal signals while maintaining the desired impedance at the input and outputs. For live audio applications a splitter functions in much the same way for providing signal feeds to both the console and to a recording device.


A receiver circuit designed to mute the audio output when the received signal is too weak to provide acceptable audio or, in some cases, when the wrong signal is being received.
(See Noise Squelch, Signal Level Squelch, Tone Coded Squelch)


In wireless, the accuracy to which the operating frequency is maintained as temperature changes over time.

Standard MIDI File

A standardized file format for exchanging MIDI data independent of originating software or platform. Comes in two flavors. Type 0, which is a single track that contains all sixteen MIDI channels and pertinent information. It should be noted that although the information is presented in a single track, the individual channel information is kept discreet and can be easily extracted. Type1 retains the multi channel format of the original sequence. It should be further noted that unlike GENERAL MIDI, there is no specification as to what sound plays on what channel. If two users have similar MIDI equipment, then imbedded patch change information will provide the correct sounds. Otherwise users have to provide additional information to allow a fellow user to realize the sequence successfully.
(See MIDI)


A microphone polar pattern that is similar to the hypercardioid pattern. The supercardioid pattern is slightly less directional and the rear sensitivity lobe is smaller.
(See Hypercardioid)


Used in reference to headphones and means “over the ear.” Can be combined with semi open, closed and open back designs.

Switching Diversity

The most common implementation of a true diversity receiver, in which the audio from the better of two receiver channels is continuously selected by means of an electronic switch.


In reference to wireless microphones, a synthesizer is a circuit that generates a stable and precise radio frequency output on any one of a number of preset frequencies. Synthesizers are used as the local oscillators for receivers, and to set the output frequency of transmitters. The term also refers to a type of electronic instrument that originally used oscillators and control voltages to create tones. These days most synthesizers use digital circuits to produce a their sounds.

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A protocol developed by Tascam for transferring up to eight channels of digital audio across a single wire, and hence known as the Tascam Digital InterFace. Originally developed for their Modular Digital Multitrack (MDM) tape machines, TDIF along with the ADAT interface, are the two most popular formats for the transfer of digital audio where more than two tracks of data are involved.


Time Division Multiplexing, a method for putting multiple data streams into a single signal. Originally developed for telephone transmission, Digidesign took the concept, applied it to multi track digital audio and today Pro Tools stands as the de facto standard in the professional audio community.


Total Harmonic Distortion. All electronic devices add some form of distortion to a signal passing through them. In audio, one form of distortion is the addition of harmonics that are not present in the original signal. THD is a measurement of this and is represented as a ratio of the total of all the harmonics added against the original signal at the output of the device. The closer THD is to zero, the less the circuit is distorting the source signal.


An optical digital audio format that uses light and fiber optic cables for transmitting data. Similar to S/PDIF data, often the two connectors are found side by side on semi-professional equipment.


Tip, Ring, and Sleeve. A type of 1/4" phone plug that looks like the plug found on stereo headphones. Used in a variety of applications, namely as a balance connector, where the tip and ring both carry the signal, as a send/return connector from an insert of a mixer, and for providing unbalanced stereo connectivity, as in headphones.


Tip, Sleeve (TS) refers to a type of 1/4" phone plug that is used for unbalanced connection.

Tap Tempo

A function found in some sequencers and effect devices that have time based effects, where tapping a virtual button or an actual physical one can change the governing tempo. From two or more successive taps, the program or device will extrapolate a tempo based on beats per minute.

Terminal Strip

Also know as a barrier strip. A series of screw terminals arranged in a line to which other devices are connected. Popular on equipment from about twenty years ago due its low cost and reliability, nowadays the connectors are mostly found on equipment such as amplifiers or crossovers that are to be installed into permanent installations.


A small device that is put on the end of certain signal chains to maintain proper impedance. For audio purposes, terminators are essential for terminating SCSI lines. Usually a set of transistors housed in a small plastic container with the correct form of plug for inserting into the final device of a chain.


A parameter that is found on dynamic based processors such as compressors, limiters and gates. The setting determines at what level the processor will begin to function. On a compressor for instance, when the source signal passes the amplitude threshold set by the user, the compressor begins to operate on the signal, and conversely, when the signal falls bellow the threshold, processing stops.


On MIDI equipped devices, the "Thru" connector simply passes on, unchanged, the information received at the "In" port

Tone Coded Squelch

Tone Coded Squelch is a way of letting a receiver know that a correct signal is being received. The tone sent is at a frequency outside human hearing and is usually combined with another type of muting, such as signal level squelch.
(See Squelch)

Toroidal Transformers

A transformer in the shape of doughnut. Although costlier to produce and tends to be larger and heavier than other forms of transformers, the shape reduces magnetic fields entering or leaving the transformer, and thus makes it desirable for high-end audio applications.


A transducer is an electronic device that converts energy from one form to another. For the purposes of audio these include microphones, loudspeakers and antenna. Although not generally thought of as transducers, other forms include LED's photocells and even the light bulb.


An electronic circuit capable of outputting or receiving a balanced audio signal without the use of a magnetic transformer.

True Diversity

A form of diversity that uses two spaced antennas and two receiver channels tuned to the same frequency. Essentially eliminates signal loss (dropouts) by instantaneously selecting the audio output from the receiver channel having the stronger RF input signal. Also referred to as space diversity or dual-receiver diversity.

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Ultra High Frequency. A range of radio frequencies that extends from 300Mhz to 3GHz. Allocated by the FCC for use by satellite systems, broadcasting and a wide range of two-way communication systems that includes wireless microphones.


Universal Serial Bus. A plug and play interface that is found on both Windows and Apple computers, that allows for connection of various peripherals without rebooting or having to add adapter cards. USB allows for up to 127 devices and supports data speeds of 12 Mbps.


With the advent of 24-bit recording, the issues of how best to lower the resolution of audio to 16-bit for CD manufacture has prompted several responses. UV-22 is a patented process developed by Apogee that is similar to many dithering schemes although they differ in where the added noise is placed. Apogee adds an inaudible, high-frequency "bias" to the digital bit stream, placing an algorithmically-generated "clump" of energy around 22 kHz.


To convey an electrical signal through wire, two conductors are required. In unbalanced circuits, one conductor carries both signal and supplies ground, unlike in balanced connections. Because of this unbalanced circuits are less expensive to produce, but the down side is the cables are susceptible to noise, especially if lengths of over 30 feet are involved.


Describes a device that radiates or receives energy more efficiently from a single direction than from all other directions. In reference to microphones, unidirectional describes a polar pick-up pattern that more sensitive to sound from one direction than others. The actual polar pattern will dictate how directional microphone actually is.

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In wireless microphones, refers to systems with operating frequencies below approximately 300MHz. In the U.S., most such systems operate somewhere between 170 and 216MHz.

VU Meter

Meter designed to interpret signal levels in a similar way to how human ears perceive loudness, responding more to the average level of sounds rather than to peak levels.

Vacuum Tube

Known in the UK as valves, tubes are devices that amplify electronic signals. With the arrival of the transistor, tubes fell out of popularity except for some very high-end audiophile equipment manufactures, but with the proliferation of digital audio workstations, tubes have seen a reemergence. Although they require much higher voltages, often around 300 volts as compared to around 10 volts for bipolar and field effect transistor, they respond better to overload conditions and are more electronically rugged. Additionally, many state that the color tube equipment imparts is a perfect companion for the digital recording medium.


An audio processor that extracts the basic component of one audio signal and then superimposes this element onto another signal. To do this, the first audio signal (a vocal for instance) is sent through a series of parallel signal filters that create a signature of the input signal, based on the frequency content and level of the frequency components. This set of filters is then used to process the second signal (a string ensemble.) The result is that the vocal imprint now modulates the string ensemble.

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Wave File

An audio file format created by Microsoft. The standard on Windows machines, the format is used for everything from system and game sounds to CD quality audio. The format has also been accepted as a viable interchange medium for other platforms such as the Mac. The file is identified by the file name extension .wav.


A representation of how alternating current varies over time. The simplest and most familiar waveform is the sine wave, but any electrical signal of any complexity will also have a waveform. In digital audio, the graphical representation of the waveform has contributed greatly to acceptance of medium, since it has become very easy to edit material while looking at a graphical representation of it.


The distance that a wave propagated in space or along a wire travels while going through a single cycle (360°). At room temperature one wavelength at 100Hz is around 11 feet, while at 10kHz the distance is reduced to about 1.3 inches. An important detail that needs to be understood in the design of acoustic spaces.


A means by which the laboratory measurements of the performance of a piece of audio equipment are modified to better take into account human aural perception. This generally delivers slightly better specifications. For example, "a-weighting" is a curve that is applied to the measurement of sound pressure levels that compensate for the way the human ear perceives loudness.

Whip Antenna

A single element antenna that can be directly attached to a wireless transmitter or receiver. The short flexible antennas found on handheld two-way radios and cell phones are examples of this type of antennas.

White Noise

A sound that contains every frequency within the range of human hearing in equal amounts. To many people white noise sounds as if it has more high frequency content, but this is because each successive octave has twice as many frequencies as the one preceding it. Pink noise is similar except that the white noise is filtered to reduce the volume at each octave. This is done to compensate for the increase in the number of frequencies per octave. Each octave is reduced by 6dB, resulting in a noise sound wave that has equal energy at every octave.


The low frequency driver in a multi driver speaker.

Word Clock

The accurate timing of digital audio data is crucial for sending data from one location to another. It is equally crucial when synchronizing multiple streams of audio data on multiple pieces of equipment. The function that makes sure each bit of data arrives when it should is called word clock. In addition word clock provides information about the start and end of each sample, and whether it belongs to left or right channel of a stereo signal. Digital interfaces such as AES/EBU and S/PDIF include word clock information embedded in their data steams, and the rate of the clock is derived from the sampling rate. Word clock can also be generated independently of any actual data. Dedicated word clock generators are often used as master clocks in a multi equipment facility or to improve the functioning (lowering jitter) of analog to digital and digital to analog converters.
(See AES/EBU, Jitter, S/PIDF)

Word Length

In digital audio, the term is used to define the number of bits a digital device uses to process audio. While sampling frequency determines the outer frequency limits that a piece of hardware is capable of processing, bit depth refers to the dynamic range that can be captured during recording. The number of possible "levels" that can be recorded at 16-bit is 65,536, while this figure jumps to 16,777,216 using 24-bit hardware. The human ear is very sensitive to these levels, and given properly implemented converter designs, 24-bit recordings will sound more "open" than 16-bit recordings. However, it is also true that a top of the line 16-bit converter could sound better than a very poorly implemented 24-bit converter. Although bits and sampling frequencies are important specifications, the kinds of filters used, and the integrity of the audio path prior to the converters is also very important as to how a particular converter will sound.
(See Floating Point)

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Yamaha's answer to Roland's GS system. Both systems are attempts to enhance the General MIDI protocol, providing additional banks of patches and further editing functionality.


A name originally trademarked by Cannon that refers to a type of connector. Used in audio for sending balanced signals and microphone feeds, an XLR connector consists of three pins housed in a barrel and often having locking components. The male side is for sends, and the female is always a receiving connector. Unfortunately manufactures have not standardized which pin, 2 or 3 is hot. Most equipment wants to see pin 2 hot, but there are exceptions, and it is important to have the correctly wired cable for it to pass signal.

XY Stereo

XY stereo set-up is a coincidence stereo technique using two cardioid microphones in the same point and angled at 90° to produce a stereo image. Theoretically, the two microphone capsules need to be at exactly the same point in space to avoid any phase problems due to the distance between the capsules. As this is not physically possible, the nearest approximation is to place one microphone on top of the other with the diaphragms vertically aligned. In this way, sound sources in the horizontal plane are picked up as if the two microphones were placed at the same point. However, channel separation is limited, and wide stereo images are not possible. But the XY stereo method is highly mono-compatible and is used in broadcasting situations where listeners might be listening to stereo audio on mono equipment.

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Y Cable

A cable used to split or combine two signals. Another use is to send a signal out of one side of the "Y" and return through the other, as when patching into an insert point of a console. There are occasions where "Y" cables should not, or cannot be used. One is for MIDI. It is impossible to combine two channels of MIDI using a "Y" cable. Combining two outputs of an amplifier is also not something that should be done. In general, "Y" cabling should be avoided except in the send/return scenario, or with propriety cables, such as Digidesign's MH069 cable, used for connecting two interfaces to a single DSP card.

Yagi Antenna

A type of directive antenna that provides moderate to high gain over a relatively limited frequency range. Commonly used in communications when the operating frequency is above 10MHz. This type of antenna is popular among Amateur Radio and Citizens Band radio operators. The driven element of the antenna is the equivalent of a center-fed, half wave dipole antenna, which in turn is surrounded by straight rods called reflectors and directors.

Yellow Book

Derived from the Red Book standard, the specification contains details for the CD-ROM format, which including track requirements, error correction and more.
(See Red Book)

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Symbol for impedance. Hi-Z, for instance means high impedance, while Lo-Z means low impedance.


A type of shock mount and windscreen for directional microphones, often used in outdoor environments with shotgun microphones. Also referred to as blimps due to the shape of the hollow, acoustically transparent basket that surrounds the microphone. Onto this basket various "muffs" can be added that increase the rejection of wind noise, but the more covering employed, the more high frequencies attenuation may occur.

Zipper Noise

A type of distortion that is heard from cheaper digital devices when changing certain parameters. It is caused by quantization, where under digital control changing values are spaced apart and stepped, as opposed to the analog domain, where such changes are continuous.

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