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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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A sliding potentiometer control used in mixers and other processors.


A type of magnetic tape coating that uses iron oxide.


Field Effect Transistor. A solid-state semiconductor device in which the current flowing between source and drain terminals is controlled by the voltage on the gate terminal. The FET is a very high impedance device, which makes it highly suited for use in impedance converter stages in capacitor and electret microphones.

FET Compressor

A form of audio compressor in which an FET is used to provide variable signal attenuation. FET compressors are fast-acting in comparison to opto-compressors.

FET — Field Effect Transistor

A solid-state semiconductor device in which the current flowing between source and drain terminals is controlled by the voltage on the gate terminal. The FET is a very high impedance device, which makes it highly suited for use in impedance converter stages in capacitor and electret microphones.


The accuracy or precision of a reproduced acoustic sound wave when compared to the electrical input signal.

Figure of Eight — Figure-Eight

Describes the polar response of a microphone or loudspeaker that is equally sensitive both front and rear, yet rejects sounds coming from the sides. Also called Bipolar.


A container for stored digital data that usually has a meaningful name. For example, a Standard MIDI File is a specific type of file designed to allow sequence information to be interchanged between different types of sequencer.


An electronic circuit designed to attenuate a specific range of frequencies. (See low-pass, high-pass and band-pass.) The amount of attenuation depends on the filter slope which is typically either 6, 12, 18 or 24dB/Octave. 

Filter Frequency

The ‘turnover’ or ‘corner’ frequency of a high- or low-pass filter. Technically, the frequency at which the signal amplitude has been attenuated by 3dB.


A serial computer interface format based upon the IEEE 1394 standard and named FireWire by Apple (Sony’s i.Link format is also the same interface). FireWire is used for high speed isochronous data transfer, including audio and video. FireWire 400 (IEEE 1394-1995 and IEEE 1394a-2000) or S400 interface transfers data at up to 400Mb/s and can operate over cables up to 4.5metres in length. The standard ‘alpha’ connector is available in four and six-connector versions, the latter able to provide power (up to 25V and 8 watts). The FireWire 800 format (IEEE 1394b-2002) or S800 interface uses a 9-wire ‘beta’ connector and can convey data at up to 800Mb/s.


An effect which combines a modulated delay with the original signal, using feedback to create a dramatic, sweeping sound.

Flash Drive (see 'Solid-state Drive')

A large capacity solid-state memory configured to work like a conventional hard drive. Used in digital cameras and audio recorders in formats such as SD and CF2 cards, as well as in ‘pen drives’ or ‘USB memory sticks’. Some computers are now available with solid-state flash drives instead of normal internal hard drives.

Floppy Disk

An obsolete computer disk format using a flexible magnetic medium encased in a protective plastic sleeve.


A high-speed variation in replay speed causing rapid 'fluttering' pitch variations. See Wow and Flutter or Scrape Flutter

Flutter Echoes

Short time-span sound echoes which can be created when sound waves bounce between opposite walls in a small or moderately sized room. A shorter version of the ‘slapback’ echo whch can be experienced in a larger hall when sound from a stage is reflected strongly from the rear wall.

FM (Frequency Modulation)

A means of convenying information on a carrier wave by varying its instantaneous frequency. In an audio application, like FM radio, the wanted audio signal's amplitude is used to create corresponding deviations in the carrier wave's frequency.  A demodulator can detect these frequency deviations and convert them back to amplitude variations to recover the base-band audio signal. This form of modulation contrasts with amplitude modulation (AM) where the carrier wave frequency remains constant and its amplitude is varied to convey the wanted signal.


Front of House — often a term used to describe a PA system, providing amplified sound to the audience, as distinctly opposed to the 'monitor system' providing foldback to the musicians or performers.


A system for making one or more separate mixes audible to musicians while performing, recording and overdubbing. Also known as a Cue mix. May be auditioned via headphones, IEMs or wedge monitors (wedge-shaped loudspeakers placed on the floor).


The frequency components or resonances of an instrument or voice sound that doesn't change with the pitch of the note being played or sung. For example, the body resonance of an acoustic guitar remains constant, regardless of the note being played.


A procedure required to ready a computer disk or digital tape for use. Formatting organises the medium into a series of ‘electronic pigeon holes’ into which data can be stored. Different computers often use different formatting systems.

Fragmentation (cf. defragment)

The process by which the available space on a disk drive gets split up into small, sometimes unusable, sections due to the storing and erasing of files.


The number of complete cycles of a repetitive waveform that occur in 1 second. A waveform which repeats once per second has a frequency of 1Hz (Hertz).

Frequency Response

The variation in amplitude relative to the signal frequency. A measurement of the frequency range that can be handled by a specific piece of electrical equipment or loudspeaker. (Also see Bandwidth)


Frequency Shift Keying. An obsolete method of recording a synchronisation control signal onto tape by representing it as two alternating tones. (Also see timecode)

Fukada Tree

A 7-microphone array surround-sound, broadly equivalent to the stereo Decca Tree. Conceived by Akira Fukada when he worked for the Japanese state broadcaster NHK. The front Left, Centre and Right outputs are generated from a trio of mics arranged in a very similar way to a Decca Tree, with the left and right outriggers spaced 2m apart, and the centre mic 1m forward. The Rear Left and Rear Right channels come from mics spaced 2m apart placed and 2m behind the front outriggers. Instead of using omni mics like a Decca Tree, all five mics are usually cardioids, aimed 60 degrees outwards to maximise channel separation. These five mics are usually supplemented with an extra pair of omni outriggers placed midway between the front and rear mics.


The lowest frequency component in a harmonically complex sound. (Also see Harmonic and Partial.)


Shorthand abbreviation for Effects.