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Welcome to Sound On Sound's indispensible, regularly updated, explanations of technical terms from the fields of Recording, Audio Production, Music Technology, MIDI, Music Software, Audio Plug-ins, Mac and PC Computing, Live Sound, Acoustics, Electronics and more...

If we do not explain a particular term below, please email and we will add it to our next update.

Last updated: 01/02/24

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Anharmonic Distortion

Anharmonic distortion involves the introduction of frequencies not musically related to the source signal, usually through some form of modulation process, such as aliasing in digital equipment which is overloaded or has poor anti-alias filtering, or scrape flutter in analogue tape machines. 

Anti-alias Filter

A very steep low-pass filter used to limit the frequency range of an analogue signal prior to A/D conversion, so that the maximum frequency does not exceed half the sampling rate. (See A-D Conversion)


See Audio Over IP

App (Application)

Alternative term for a computer program.

Arming (Arm)

Arming a track or channel on a recording device places it in a condition where it is ready to record audio when the system is placed in record mode. Unarmed tracks won’t record audio even if the system is in record mode. When a track is armed the system monitoring usually auditions the input signal throughout the recording, whereas unarmed tracks usually replay any previously recorded audio.


A device (or software) that allows a synthesizer or MIDI instrument to sequence around any notes currently being played. Most arpeggiators also allow the sound to be sequenced over several octaves, so that holding down a simple chord can result in an impressive repeating sequence of notes.


Acronymn for American Standard Code for Information Interchange (pronounced 'askey'). An internationally recognised code used to represent computer keyboard characters.


Advanced Tranmission Line — a term coined by PMC Loudspeakers to describe the specific vented-cabinet design employed in all of their loudspeakers. (See Bass Reflex and Transmission-Line)


The time taken for a sound to achieve its maximum amplitude, or for an electronic device to reach the full extent of its action. Drums generally have a fast attack, whereas bowed strings typically have a slow attack. In compressors and gates, the attack time equates to how quickly the processor can reduce the signal level.


To reduce the signal amplitude or level. Normally specified in terms of (negative) decibels.

Audio Data Reduction

A system used to reduce the amount of data needed to represent some information, such as an audio signal. Lossless audio data reduction systems, (eg. FLAC and ALAC) can fully and precisely reconstruct the original audio data with bit-accuracy, but the amount of data reduction is rarely much more than 2:1. Lossy data audio reduction systems (eg. MPEG, AAC, AC3 and others) permanently discard audio information that is deemed to have been 'masked' by more prominent sounds. The original data can never be retrieved, but the reduction in total data can be considerable (12:1 is common).

Audio Frequency

Signals in the range of human audio audibility. Measured in Hertz and nominally between 20Hz and 20kHz.

Audio Interface

A hardware device which acts as the physical bridge between the computer’s workstation software and the recording environment. An audio interface may be connected to the computer (via USB, Thunderbolt, FireWire, Dante, AVB or other current communication protocols) to pass audio and MIDI data to and from the computer. Audio Interfaces are available with a wide variety of different facilities including microphone preamps, DI inputs, analogue line inputs, ADAT or S/PDIF digital inputs, analogue line and digital outputs, headphone outputs, and so on. The smallest audio interfaces provide just two channels in and out, while the largest may offer 30 or more.

Audio Over IP

Also known as AoIP — an audio transfer system which routes multiple audio channels over an Ethernet network. There is a wide range of systems operating in slightly different ways, few of which are compatible. Some require independent and exclusive networks, while others can co-exist with existing Ethernet traffic. Examples of proprietary AoIP systems include, Ravenna, Dante, and many more, but there are also a few generic systems such as AVB

Audio Random Access (ARA)

Jointly developed by Celemony and PreSonus in 2011, ARA relates to a data-exchange extension for DAW plug‑ins like AU, VST and RTAS, to pass information relating to an entire track, rather than just about a specific moment in time — such as pitch, tempo, rhythm etc. ARA v2 was announced in 2018 with an extended feature set including integrated undo synchronisation. Most of the popular DAWs are now compatible with ARA v2, but the only plug-ins that use it at the time of writing are Melodyne and Revoice Pro.

Audio Video Bridging (AVB)

Audio Video Bridging (AVB) is a a suite of IEEE technical standards intended to allow the low latency, time-synchronised transfer of audio and video data across standard IT Ethernet networks. It is a 'Layer 2' AoIP protocol, defined under the IEEE 802 standards. The AVnu Alliance certifies consumer and professional AVB equipment to ensure inter-operability. 

In essence, the AVB standard reserves for audio/video data traffic a certain amount of data bandwidth on a standard Ethernet network, and precise synchronisation of that data at the receiver is achieved using a 'generalised precision time protocol' (gPTP) which is also defined as part of the IEEE 802 standards.

In theory, AVB traffic can coexist within a standard IT network, although AVB-capable switches are required to reserve the necessary bandwidth and to ensure data synchronisation. Data is transmitted as a multicast (one sender, multiple listeners) within defined timeslots to avoid collisions. It is also categorised for priority with Class A (professional) traffic having a guaranteed latency of 2ms, whereas Class B (consumer) traffic has a guaranteed latency of 50ms.  


Auto-Tune was registered as a trademark of Antares in 1997 for its innovative automatic pitch correction processor.  Now largely used as a generic term for all such processes from a wide range of hardware and software manufacturers of pitch-correcting products.


A common facility on tape machines or other recording devices that enables specific time points to be stored and recalled. For example, you may store the start of a verse as a locate point ('marker') so that you can get the tape machine or DAW to automatically relocate the start of the verse after you've recorded an overdub.

Aux Return

Dedicated mixer inputs used to receive external effects into the mix. Aux return channels usually have fewer facilities than normal mixer inputs, such as no EQ and access to fewer auxiliary sends. (cf. Effects Return)

Auxiliary Sends (Auxes)

A separate independent output signal derived from one or more input channels on a mixing console, usually with the option to select a pre- or post-fader source and to adjust the contribution level. Auxiliary sends from all channels are bused together before being made available to feed an internal signal processor or external physical output via the corresponding Aux Master level control. Sometimes also called Effects ('FX'), Cue or Artist sends.


The alignment of a tape head which references the head gap to the true vertical relative to the tape path. (cf. 'Wrap' and 'Zenith').