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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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See Public Address System


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.

Parallel Compression

A method of controlling dynamic range in which the source signal is split, with one path being heavily compressed before being recombined with the original signal. The result is a form of 'upwards compression' in which low level signals are raised in level while high level elements are left unchanged. This technique preserves transients and is therefore particularlty popular for processing drum tracks. (Conventional downwards compression inherently modifies transients.)

Often known as New York Compression, and as London Compression! 

There is a full explanation of the technique here:


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

Parametric EQ

An equaliser with a bell-shaped frequency response curve, and separate controls for the centre frequency, the bandwidth (Q), and the amount of cut/boost. If a bell EQ omits the bandwidth (Q) control, it is known as semei- or quasi-paramteric.


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 channel signal, prior to the fader, and thus independent of the fader setting. Normally used to check the level of the signal through the channel to optimise the gain structure, or to confirm the presence of a signal before fading it up. (See AFL and Solo)

Phantom Power

Phantom Power is a standardised professional method of providing power to the electronics of some types of microphones via a balanced XLR connection. The relevant standard was first conceived in the early 1970s, and is now recognised as IEC 61938:2018. Several variations of phantom power are detailed in the document. 

Most professional systems operate with a nominal supply voltage of +48V DC, although there is an acceptable tolerance range of +/-4V (ie. 44 to 52V). This arrangement is described as the 'P48' format, and the phantom power supply is connected with the positive side going to each of the two balanced audio lines via individual 6k8 current-limiting resistors. The negative side is returned via the cable screen. In this configuration the maximum current available to the microphone is 10mA, providing up to 170mW of power. Most microphones draw around 4mA (or less) of current, but some models require more and a few need the full 10mA .

Battery-powered equipment often uses the P12 format, which uses a 12V power supply with 680 Ohm feed resistors allowing up to 15mA and 100mW of power. A newer addition to the specification, called P12L (low-power), uses 3k3 resistors to give 4mA and just 22mW of power.

At the other end of the scale is the new SP48 variation which uses the 48V supply voltage but connects via 2.2K feed resistors allowing up to 22mA and 520mW of power. 

Although rare, some manufacturers choose to provide non-standard supply voltages, such as 15 or 24V — something which seems prevalent on budget, compact, active PA loudspeakers. Some microphones are very tolerant of the supply voltage (many AKG mics can accept anything from 9-52V, for example), while others won't function correctly if the supply voltage falls too low.

Other microphone powering schemes are also available, including 'Plug-in Power' for consumer electret and lavalier mics, and Tonader (or A-B) power for battery-powered legacy professional equipment. 


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 plosive is the strong puff of air from the mouth which is generated when speaking or singing syllables with 'b's or 'p's. if a plosive blast reaches a microphone's diaphragm it can create a large unwanted low-frequency signal and distortion (see Wind-shield).


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

Plug-in (or Bias) Power is a method of providing power to the internal electronics of electret microphones, and is commonly used on consumer equipment. Plug-in Power is only ever provided on 3.5mm mini-jack input sockets as found on domestic sound recorders, 'phones, laptops etc. The format provides a low DC voltage of typically between 3 and 5V, with the positive side of the power supply connected to the unbalanced signal connection(s) in the mini-jack socket. So the tip connection for a mono input, or tip and ring connections for a stereo input. The negative return is via the sleeve connection.

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'.