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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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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 sample rate must be more than twice the highest frequency to be encoded — according to the Nyquist Theorem.

Sample Rate Converter (SRC)

(SRC) A digital processor or computer algorithm able to convert digital audio signals recorded at one sample rate to a completely different sample rate, eg. from 96kHz to 44.1kHz. In the case of a downward conversion, the appropriate anti-alias filtering is applied to ensure the new file doesn't contain any source componets above half the new sample rate. For an upward conversion, the upper regions of the bandwidth in the new sample rate will carry no information as there was none available in the source file due to the restrictions of its lower sample rate. Not all SRCs are as accurate as they should be, but the best are essentially a perfect and transparent process.


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.


Saturation is a mild form of dynamic and harmonic distortion typically associated with bringing 'warmth' and 'body' to a sound. The term relates to a process which can occur in transformers when the magnetic flux generated by the input signal fully magnetises the transformer core such that it cannot then accurately pass any larger audio signals, resulting in audio compression and harmonic distortion. A similar effect can occur with magnetic tape heads and tape itself. These saturation effects can now be emulated electronically and digitally, often with user controls to fine tune the effect characteristics. 

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.


The terms screening or shielding normally refer to a method of preventing external electromagnetic interference reaching sensitive electronic circuitry by encasing it within an electrically conductive enclosure, often referred to as a Faraday Cage.

The shielding works by distributing the electrical charges induced by an external electrical field in such a way their influence is cancelled out in the interior.

Often, the shielding enclosure is connected to ground, to drain away any induced currents, although this isn't strictly necessary.

Most electronic equipment is housed within a metal chassis, and most cables have an outer shield or screening layer in their construction, specifically to minimise the unwanted interference from external fields. 

This SOS article discusses the many variations of cable shielding technologies.


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.


Small Diaphragm Capacitor microphone — a microphone with a diaphragm diameter of between about 10 and 15mm 


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.

Shelf Equaliser

High and low shelf equalisers affect the high or low frequencies, respectively, raising  or lower the level of all frequencies in the corresponding band by the same amount. Consequently, the frequency response looks a bit like a shelf above or below the rest of the audio band. Sometimes also known as bass and treble tone controls.


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 which has a waveform defined by a mathematical function derived from a classic periodic oscillation, such as the movement of the tip of swinging pendulum. In a musical context, a sine wave contains only a single fundamental frequency, and  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.


Solo In Place (see Solo).


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.


Used in the context of filters and equalisers, the term refers to the gradient or steepness of the change in signal amplitude at the turnover frequency. First-order filters have a slope of 6dB/octave, while second-order is 12dB/octave and third-order is 18dB/octave. The steepest slope typically found in audio filters (ususally in synthesizers and loudspeaker crossovers) is 24dB/Octave (fourth-order). Shelf equalisers normally have 6dB/octave slopes.  


see Switching Power Supply