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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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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’.


A system used within mixing consoles to allow specific channel signals to be monitored in isolation. Solo differs from PFL and AFL in that it doesn't route signals to the monitoring system via a dedicated bus. Instead, it uses the console's main stereo output bus and works by muting all other channels, leaving only the channel currently being solo'd to feed the stereo mix bus. For this reason, it is often called a 'destructive solo' and the function is normally locked-out in broadcast desks when the 'red light' is turned on! As the Solo'd signal includes the effects of both the fader and the pan-pot, it is sometimes known as 'solo-in-place, or SIP. (See AFL and PFL).

Solo Safe

Large format consoles ofgten have a 'Solo Safe' function to prevent certain channels from being muted when others are solo'd. This would typically be used to maintain the signals from effects returns, for example, so that a solo'd channel can be auditioned with its related effects. (See Solo)

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).

Square Wave

A symmetrical rectangular waveform. Square waves contain a series of odd harmonics.


see Stereo Recording Angle


see Solid-state Drive.


In the context of electronic audio equipment, a stage is a functional block of circuitry that performs a specific task. For example, a 'four-stage' phaser effects pedal employs four all-pass filter circuits. An individual stage could be a preamplifier, an insert return buffer, a section of an equaliser, or a mix-bus amplifier, for example, and the process of optimising the signal level passing through each stage is called gain-staging

Stage Box

A connection box terminating a multicore cable (see Snake) which is usually placed on a stage for the easy connection of individual microphone cables.

Standard Midi File

A standard file format that allows MIDI files to be transferred between different sequencers and MIDI file players.

Standing Waves

Resonant low frequency sound waves bouncing between opposite surfaces such that each reflected wave aligns perfectly with previous waves to create static areas of maximum and minimum sound pressure within the room. (See also Modes and Modal Frequencies)

Star Mains Distribution

An arrangement of distributing mains power in project studios which minimises the risk of creating inadvertant ground-loops. In Star distribution a mains plug-board is plugged into the wall outlet, and if further sockets are required additional plugboards are plugged directly into the first board. in this way, mains current follows the most direct path back to the wall socket.

Star vs Daisy-chain graphic

This configuration is very different to the 'Daisy-Chain' approach, where additional plug-boards are connected to each other to form a chain. In this arrangement, current drawn by the device plugged into the last board has to flow through all the others, greatly increasing the risk of voltage drops along the earth path and thus leading to unwanted ground-loop noises.


When mixing complex audio material it is often useful to divide the tracks into related sections and mix those sections separately before combining the whole. In mixing film soundtracks, the material would often be grouped as a dialogue stem, a music stem, and an effects stem. Each stem might be mono, stereo or multichannel, as appropriate to the situation. In music mixing, stems might be used for the rhythm section, backline instruments, frontline instruments, backing vocals, lead vocals and effects - or any other combination that suited the particular project.

Step Time

A system for programming a sequencer in non-real time.


By convention, two channels of related audio which can create the impression of separate sound source positions when auditioned on a pair of loudspeakers or headphones.

Stereo Imaging

Stereo Imaging refers to the accuracy and quality of the spatial positional information being portrayed for individual sound sources within a stereo soundstage reproduced by stereo loudspeakers or headphones. 

Stereo Recording Angle

The angle over which sound sources can be captured by a microphone array. For a stereo array with a stereo recording angle of 90 degrees, sound sources can be placed ±45 degree relative to the array’s centre front axis, with a source at the extreme angle appearing fully left or right in the stereo image.

Sticky Shed Syndrome

A problem affecting some brands of analogue tape after a long time in storage. A breakdown of the binder causes the oxide to shed, and the tape tends to adhere to the tape heads and guides when played. A short term cure can be affected by baking the affected tape.


The practice of recording a time code signal onto one track of a multitrack tape machine to facilitate subsequent synchronisation.


Frequencies below the range of typical monitor loudspeakers. Some define sub-bass as frequencies that can be felt rather than heard.


Hidden data within the CD and DAT format that includes such information as the absolute time location, number of tracks, total running time and so on.


A subharmonic is a component of a periodic wave which has a frequency lower than the declared fundamental. As an example, a component with half the frequency of the fundamental would be the second subharmonic, and whereas the harmonic series are defined by the arithmetic multiplication of the fundamental frequency, subharmonics involve the arithmetic division of the fundamental frequency. Subharmonics can be generated by using special playing techniques in a few musical instruments (such as overblowing on some wind instruments), but are more often created artificially, if required.

Subtractive Synthesis

The process of creating a new sound by filtering and shaping a raw, harmonically complex waveform.


A specific type of efficient loudspeaker system intended to reproduce only the lowest frequencies (typically below 120Hz).


A sudden increase in mains voltage.


The use of multiple loudspeakers placed around the listening position with the aim of reproducing a sense of envelopment within a soundstage. Numerous surround formats exist, but the most common currently is the 5.1 configuration in which three loudspeakers are placed in front of the listener (at ±30 degrees and straight ahead), with two behind (at ±120 degrees or thereabouts), supplemented with a separate subwoofer.