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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: 04/08/20

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A resistive circuit for reducing signal level.


A control found on mixers to move the signal to any point in the stereo soundstage by varying the relative levels fed to the left and right stereo outputs.


A means of connecting two or more circuits together so that their inputs are connected together, and their outputs are all connected together.


A variable value that affects some aspect of a device's performance.

Parameteric EQ

An equaliser with separate controls for frequency, bandwidth and cut/boost.


Often used to descibe a multi-oscillator mono-synth which can be configured to allow the oscillators to be controlled independently from the keyboard, allowing two or more notes to be played simultaneously.


The combination of fundamental and overtones together are called particals. (cf. harmonic)


A circuit with no active elements.

Passive Loudspeaker or Monitor

A loudspeaker which requires an external power amplifier, the signal from which is passed to a passive cross-over filter. This splits and filters the signal to feed the two (or more) drive units.


An alternative term for a Program, referring to a single programmed sound within a synthesizer that can be called up using Program Change commands. MIDI effects units and samplers also have patches. (see also Bank)

Patch Cord

A short cable used with patch bays.

Patchbay (Patch Bay)

A system of panel-mounted connectors used to bring inputs and outputs to a central point from where they can be routed using plug-in patch cords. Also called a Jackfield.

PCI Card

Peripheral Component Interconnect: an internal computer bus format used to integrating hardware devices such as sound cards. The PCI Local Bus has superseded earlier internal bus systems such as ISA and VESA, and although still very common on contemporary motherboards has, itself, now been superseded by faster interfaces such as PCI-X and PCI Express.


Pulse Code Modulation - the technique used by most digital audio systems to encode audio as binary data.


The maximum instantaneous level of a signal.


The practice of removing all headroom to maximise the peak level of an audio signal on a particular medium. So all peak-normalised material will have the same maximum peak value, but the perceived loudness is likely to vary between different tracks. The technique became popular and commonplace with the advent of digital formats such as CD, where the signal level was typically engineered to reach 0dBFS. (See also Loudness-Normalisation, Mastering and Loudness Wars)


Pre-Fade Listen. A system used within a mixing console to allow the operator to audition a selected signal, regardless of the position of the fader controlling that signal.


The relative position of a point within a cyclical signal, expressed in degrees where 360 degrees corresponds to one full cycle. (Also see Polarity)


An effect which combines a signal with a phase-shifted version of itself to produce creative comb-filtering effects. Most phasers are controlled by means of an LFO.

Phono plug (RCA-phono)

An audio connector developed by RCA and used extensively on hi-fi and semi-pro, unbalanced audio equipment. Also used for the electrical form of S/PDIF digital signals, and occasionally for video signals.


The part of a guitar that converts the string vibrations to electrical signals. Also the stylus/cartridge assembly used to replay vinyl records.

Pink Noise

A random signal with a power spectral density which is inversely proportional to the frequency. Each octave carries an equal amount of noise power. Pink noise sounds natural, and resembles the sound of a waterfall. (cf. White Noise)


The musical interpretation of an audio frequency.


A special control message specifically designed to produce a change in pitch in response to the movement of a pitch bend wheel or lever. Pitch bend data can be recorded and edited, just like any other MIDI controller data, even though it isn't part of the Controller message group.


A device for changing the pitch of an audio signal without changing its duration.


A self-contained software signal processor, such as an Equaliser or Compressor, which can be ‘inserted’ into the notional signal path of a DAW. Plug-ins are available in a myriad of different forms and functions, and produced by the DAW manufacturers or third-party developers. Most plug-ins run natively on the computer’s processor, but some require bespoke DSP hardware. The VST format is the most common cross-platform plug-in format, although there are several others.

Plug-in Power

Consumer recorders, such as MP3 recorders, are often equipped with a microphone powering system called ‘Plug-In Power’. This operates with a much lower voltage (typically 1.5V) and is not compatible with phantom-powered mics at all.

Polar Pattern

The directional characteristic of a microphone (omni, cardioid, figure-eight, etc).


This refers to a signal's voltage above or below the median line. Inverting the polarity of a signal swaps the positive voltage to negative voltage and vice versa. This condition is often referred to (incorrectly) as 'out-of-phase'.

Poly Mode

The most common MIDI mode that allows an instrument to respond to multiple simultaneous notes transmitted on a single MIDI channel.


The ability of an instrument to play two or more notes simultaneously. An instrument which can only play one note at a time is described as monophonic.


A synthesizer that can play/sound more than one note at a time (eg. eight or 16 notes), each with an independent signal chain of oscillators, filters, and envelope generators.

Pop Shield

A device placed between a sound source and a microphone to trap wind blasts - such as those created by a vocalist’s plosives (Bs, Ps and so on) - which would otherwise cause loud popping noises as the microphone diaphragm is over- driven. Most are constructed from multiple layers of a fine wire or nylon mesh, although more modern designs tend to use open-cell foam.


A connection for the input or output of data.


A gliding effect that allows a sound to change pitch at a gradual rate, rather than abruptly, when a new key is pressed or MIDI note sent.


A signal derived from the channel path of a mixer after the channel fader. A post-fade aux send level follows any channel fader changes. Normally used for feeding effects devices.