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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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Sample Multiplexing (see ADAT ).


Sony/Philips Digital Interface. Pronounced either ‘S-peedif’ or ‘Spudif’. A stereo or dual-channel self-clocking digital interfacing standard employed by Sony and Philips in consumer digital hi-fi products. The S/PDIF signal is essentially identical in data format to the professional AES3 interface, and is available as either an unbalanced electrical interface (using phono connectors and 75ohm coaxial cable), or as an optical interface called TOSlink.

Safety Copy

A copy or clone of an original tape for use in case of loss or damage to the original.


Either a defined short piece of audio which can be replayed under MIDI control; or a single discrete time element forming part of a digital audio signal.

Sample and Hold

(S&H) - Usually refers to a feature whereby random amplitude values are generated at regular intervals and then used to control another function such as pitch or filter frequency. Sample and hold circuits were also used in old analogue synthesizers to 'remember' the note being played after a key had been released.

Sample Rate

The number of times an A/D converter samples the incoming waveform each second.


The acronym stands for 'Serial Advanced Technology Attachment' and is a computer interface employed for connecting standard ATA hard drives to a computer motherboard. The SATA interface supersedes the PATA (parallel ATA) interface which has been used since the 1980s. A variant of the SATA interface, called eSATA (with the 'e' standing for 'external'), permits the connection of external hard drives. It uses a slightly different connector but is otherwise a very similar interface.

Sawtooth Wave

So called because it resembles the teeth of a saw, this waveform contains both odd and even harmonics.

Scrape Flutter

As analogue recording tape moves across the heads or other non-moving parts in the tape path it can vibrate at a high frquency (typically above 100Hz) due to a rapid stick-slip action, and this causes a form of intermodulation distortion. Often mechanical dampers and rollers are placed in the tape path to prevent scrape flutter.


A term taken from the practice of editing analogue tape where the tape was manually dragged back and forth across the replay head to locate the required edit point using an action similar to the cleaning action of 'scrubbing'. The term is now routinely used in DAWs and audio editing software platforms where the audio is played forwards or backwards at variable speeds, usually to locate an edit or cue point. A Jog Wheel is often used as the hardware controller for scrubbing.


Pronounced 'Skuzzy', it is an abbreviation for Small Computer Systems Interface. A now obsolete interfacing system for using hard drives, scanners, CD-ROM drives and similar peripherals with a computer. Each SCSI device has its own ID number and no two SCSI devices in the same chain must be set to the same number. The last SCSI device in the chain should be terminated, either via an internal terminator or via a plug-in terminator fitted to a free SCSI socket.


A device for recording and replaying MIDI data, usually in a multitrack format, allowing complex compositions to be built up a part at a time.

Session Tape

The original tape recording made during a recording session.


a mechanical isolator intended to prevent the transfer of vibrations which may be transmitted through a microphone stand from reaching a microphone where they would otherwise produce unwanted low frequency sound.


A very low resistance path that allows electrical current to flow. The term is usually used to describe a current path that exists through a fault condition. (See Open Circuit)


A high-frequency whistling or lisping sound that affects vocal recordings, due either to poor mic technique or excessive HF equalisation.


A part of an audio circuit that splits off a proportion of the main signal to be processed in some way. Compressors use a side-chain process to derive a control signals to adjust the main path attenuation.


An electrical representation of an audio event.

Signal Chain

The route taken by a signal from the input of a system to the output.

Signal-to-noise Ratio

The ratio of nominal or maximum signal level to the residual noise floor, expressed in decibels and often written as S/N.

Sine Wave

The waveform of a pure sinusoidal tone with no harmonics.

Single-ended Noise Reduction

A device for removing or attenuating the noise component of a recording or transmission system without pre-conditioning the signal. Most digital noise-reduction systems are of the Single-ended type.


The term 'slate' comes from the silent film practice of writing the scene, take and shot numbers with chalk on a slate and holding it up in front of the camera before the action starts, so that the film editor can identify the material. A role now replaced by the 'clapper-board' which adds an audio synchronisation marking facility as well. In an audio context, a slate is a verbal identification recorded just before each take to help identify it subsequently. This is normally achieved by using a talkback microphone routed to the main, group and/or direct outputs of a mixer. The console slate function often mixed a low frequency tone in with the microphone signal to help make locating the start of each take much easier when fast-winding the tape against the playback head. Each slate ident would be heard as a short, steady mid-frequency tone.


A device under the control of a master device. Often used to refer to synchronised recorders, or digital clocking devices.


see Switching Power Supply


The Society of Motion Picture and Television Engineers ( an American standards body. The term is also used to refer to a form of time code developed for the film industry but now extensively used in music and recording. SMPTE is a real-time digital code describing hours, minutes, seconds and film or video frames. Usually conveyed as an audible warble.


A term used to describe a cable used to carry multiple individual audio signals, typically between a stage and mixing console in live sound applications.

Solid-state Drive (cf. Hard Disk Drive)

A large capacity solid-state memory configured to work like a conventional hard disk drive, referred to as SSD. Some computers are now available with solid-state flash drives instead of normal internal hard disk drives. Also 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’.

Sound Card

A dedicated interface to transfer audio signals in and out of a computer. A Sound Card can be installed internally, or connected externally via USB2 or FireWire, and they are available in a wide range of formats, accommodating multiple analogue or digital audio signals (or both) in and out, as well as MIDI data in and out.

Sound On Sound

An early recording technique pioneered by Les Paul and others which was a simple form of overdubbing to build up a mix of sources. Also, the world's best recording technology magazine (see


The use of materials and construction techniques with the aim of preventing unwanted sound from entering or leaving a room.

Spaced Array

A means of arranging two or more microphone capsules such that they receive sound waves from different directions at different times - these timing differences being used to convey information about the relatice directions of those sound sources. The technique is usually used with omnidirectional microphones, although directional mics can also be employed. The best known form of spaced array is the Decca Tree. Mono-compatibility is often reduced because the timing differences between channels often results in comb-filtering colouration when the channels are summed to mono.

Speaker (also Loudspeaker and Monitor)

An accurate loudspeaker intended for critical sound auditioning purposes.


Unwanted sound picked up by microphones on one instrument from other nearby instruments.


Sound Pressure Level. A measure of the intensity of an acoustic sound wave. Normally specified in terms of Pascals for an absolute value, or relative to the typical sensitivity of human hearing. One Pascal is 94dB SPL, or to relate it to atmospheric pressures, 0.00001 Bar or 0.000145psi!


Song Position Pointer (MIDI).