Music Production Glossary

A handy A-Z of the abbreviations, acronyms and jargon used in music production.

Attack, Decay, Sustain, Release – The common parameters of an audio envelope
The process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy.
The science of sound, including its production, transmission, and effects.
a) The natural reverberation of sound within a space, also referred to as “Room Acoustics”.
b) The sounds of a given location or space
The level of sound pressure or voltage
Analog Audio
An electrical representation of sound waves where the instantaneous voltage of the signal varies continuously with the pressure of the sound waves.
Anechoic Chamber
A room free from reverberation or any other reflections.
To decrease the level of a signal
An adjustable resistive network that allows you to decrease the level of the microphone signal so that there is no overload of the mic preamplifier or the input transformer.
Audio Interface
A device used to convert analog audio signals into digital for editing and mixing in a digital audio workstation (DAW)
Beats Per Minute, a measurement used to express the tempo (speed) of a song.
Background Noise
Noise unrelated to a particular sound that is the primary object of interest
The front face of a loudspeaker, serves as the mounting surface for the tweeter, woofer and subwoofer.
The baffle also prevents sound from the front and the back of the drivers from colliding and causing noise interference.
The relative level of loudness of the various tracks that you are recording. Before studios were equipped with various sound processors the act of mixing a recording was simply called balancing and Mixing Engineers were called Balance Engineers.
Balance may also refer to the relative level of the left and right channels of a stereo signal
Balanced Audio
An audio signal of two equal but opposite polarity signals, on two conductors. Balanced cables reduce susceptibility to internal and external noise. Balanced connectors are usually three-pin XLR or 14 inch (6.35 mm) TRS jack connectors.
Bandpass Filter 
A filter that attenuates signals both below and above the desired frequency band.
The difference between the upper and lower frequencies in a continuous band of frequencies. It is typically measured in hertz.
The lower range of audible frequencies, 20-200Hz. The range of frequencies from 20-60hz is also referred to as “sub bass”.
Bi-directional Microphone
A microphone that is sensitive to sound coming from two sides, the front and the back, and all sounds coming from the sides are rejected. Also referred to as a “figure of 8” polar pattern.
Binaural Recording 
A 2-channel recording where two microphones are placed at two sides of a dummy head. This recreates the effect of the sound being received at each ear. This kind of recording is ideal for being heard on headphones.
Bit Depth
The resolution of an audio file on the amplitude axis of the waveform. The higher the bit-depth, the more dynamic range that can be captured. So a 24-bit system has a higher resolution than a 16-bit system.
The leakage of one audio source’s output into another audio source’s input. EG, a drum or cymbal’s sound bleeding into a guitar amp mic, or the output from a singer’s headphones leaking into the vocal mic. Also referred to as “spill”.
Boundary Microphone
A type of microphone designed to be mounted on an acoustically reflective surface.
A song section that is either percussive or instrumental and has a different structure from the verse or chorus.
A break section of a song consisting of just drums.
The amount of data recording software can handle at a time. Lower buffer sizes result in lower latency but the computer is more susceptible to glitches. Higher buffer sizes have longer latency but the computer is less susceptible to glitches.
CV or Control Voltage is an analog method of controlling synthesizers, drum machines and other similar equipment with external sequencers.
Early implementations were found in the Moog synthesizers of the 60s and 70s it was superseded by the MIDI protocol that was released in 1983.
Cardioid Microphone 
A directional microphone with a heart-shaped pattern of sensitivity.
Channel Strip
A chain of audio processors connected in series, usually includes a pre-amp, equalisation and pan. Some designs also offer other facilities including audio compression, de-essing, noise-gating and limiting.
May be a stand-alone unit or one of many units built into a mixing desk
Chorus (Effect)
An effect where the original signal is split into two signals and one is varied in time in relation to the original by use of a variable oscillator (the speed control). The second signal is also detuned by an amount determined by another variable oscillator (the depth control). It can produce the illusion of two instruments playing the same notes.
Chorus (Song Structure)
A section of song, usually repeated, that often contains or summarises the main message of the song.
Also referred to as the “refrain” or “hook”, although a “hook” can also refer to the melody in a verse.
A type of distortion that occurs when an amplifier is driven into an overload condition. Usually the “clipped” waveform contains an excess of high-frequency energy. The sound becomes hard and edgy.
A subjective term used to describe subtle types of alteration or distortion of sound. Colouration adds something not in the original sound. The colouration may be aurally pleasant, but it is not as accurate as the original signal.
Comb Filter
A filter implemented by adding a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced notches, giving the appearance of a comb.
An audio processor that reduces the dynamic range of an audio signal.
Condenser Microphone
A capacitor-based microphone that converts sound waves into an electrical signal. Requires power, either 48v “Phantom Power” or a dedicated power supply.
The attachment on the end of an audio cable that allows it to connect equipment together.
The most common connectors used in professional audio are XLR and TRS jacks.
Contact Microphone
A microphone that picks up vibrations through sold materials, rather than picking up sound waves travelling through the air like other microphones. Also know as a piezoelectric vibration transducer, they are most commonly used for guitars and other acoustic instruments.
One signal fading out, while another sound fades in simultaneously
Cycles per second
The frequency of an electrical signal or sound wave. Measured in Hertz (Hz)
An abbreviation of Digital Audio Tape, but often used to refer to DAT recorders (more correctly known as R-DAT because they use a rotating head similar to a video recorder). Digital recorders using fixed or stationary heads (such as DCC) are known as S-DAT machines.
DAW (Digital Audio Workstation)
A computer-based recording and editing machine used for processing and manipulating sounds.
DC Offset
Audio signals are conveyed electrically as an ‘alternating current’ or ‘AC’ signal. This might typically result in a signal voltage that varies, for example, between +3 Volts and -3 Volts, with a waveform that is more or less symmetrical about the 0V line. However, there are circumstances — often, but not always, as the result of a fault condition — where instead of alternating equally above and below zero volts, the signal voltage is offset, so it might now vary between, say, +4V and -2V. In this example it would have a DC-Offset of +1 Volt.
DC-Offsets are generally considered a bad thing, as they can result in audible clicks when editing the audio material, they can result in premature asymmetrical clipping (eg, positive peaks clipping before negative peaks), they can confuse level metering systems, and they can even cause damage to loudspeakers and headphones in some specific circumstances. 
As the DC-offset ‘signal’ effectively has a frequency of 0Hz, a DC-Offset can be removed with a high-pass filter set to a few Hertz (typically 3 or 5Hz, but anything with a turnover below 20Hz would get the job done).
Digitally Controlled Amplifier. The digital equivalent of a VCA often found in digital synthesisers and mixing consoles.
An abbreviation for ‘Direct Instrument’ or ‘Direct Inject’. Used when an electrical sound source (eg electric guitar, bass or keyboard) is connected directly into an audio chain, rather than captured with a microphone in front of a amp/loudspeaker.
DI Box
Direct Injection, or Direct Instrument Box. A device which accepts the signal input from a guitar, bass, or keyboard and conditions it to conform to the requirements of a microphone signal at the output. The output is a mic-level, balanced signal with a low source impedance, capable of driving long mic cables. There is usually a facility to break the ground continuity between mic cable and source to avoid unwanted ground loop noises. Both active and passive versions are available, the former requiring power from internal batteries or phantom power via the mic cable. Active DI boxes generally have higher input impedances than passive types and are generally considered to sound better.
A signal processor that works to remove the sibilance from sound recordings, usually vocals. It does so by reducing the dynamic range of the higher frequencies of the sound, 5-20khz.
The progressive reduction in amplitude of a sound or electrical signal over time, eg. The reverb decay of a room. In the context of an ADSR envelope shaper, the Decay phase starts as soon as the Attack phase has reached its maximum level.
Decibels (dB)
 A relative unit of measurement corresponding to one tenth of a bel (B), used to measure sound pressure levels. it is a logarithmic ratio.
A device intended to prevent the transmission of physical vibration over a specific frequency range, such as a rubber or foam block. Also called an Isolator.
The time between a sound or control signal being generated and it auditioned or taking effect, measured in seconds. Often referred to as latency in the context of computer audio interfaces.
The thin membrane in a microphone which moves in response to sound waves.
The bending of sound waves around an object which is physically smaller than the wavelength of the sound.
Digital Audio
A means of representing information (eg audio or video signals) in the form of binary codes comprising strings of 1s and 0s, or their electrical or physical equivalents. Digital audio circuitry uses discrete voltages or currents to represent the audio signal at specific moments in time (samples). A properly engineered digital system has infinite resolution, the same as an analogue system, but the audio bandwidth is restricted by the sample rate, and the signal-noise ratio (or dynamic range) is restricted by the word-length.
A mathematical construct in which a higher bit digital sample is converted to a lower bit sample such as a 24 bit to 16 bit. This is necessary because CD’s are produced using a 16bit file.
Doppler Effect
The change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
When the level of one audio signal is reduced by the presence of another signal, usually achieved using a sidechain compressor.
Dynamic Microphone
A microphone that works via electromagnetic induction, also known as a “moving coil microphone”.
A dynamic microphone works in exactly the same way as a loudspeaker, in reverse.
Dynamic Range
The difference between the loudest and quietest portions of audio, usually measured in decibels.
Combination of reverb and delay
A customizable parameter that alters a certain aspect of a sound over time
Equalization (EQ)
An effect where particular bands of the sonic spectrum are boosted or cut
A potentiometer with a sliding control. Usually used to control the level of channel on a mixing desk.
When the original signal is fed back into the circuit, a loop is created that regenerates until the circuit is overloaded.. The result can be undesirable as in squealing microphonic feedback or can be desirable as when a electric guitarist uses feedback in a musical context
A subjective measurement of sound quality, or more specifically the faithfulness to the original.
Used most commonly in domestic audio, IE HiFi (High Fidelity).
Fletcher Munson Curve
This shows how our ears are sensitive to equal loudness throughout the frequency range. For example, while listening to a song at a low volume, the person will perceive that the higher and lower frequencies will be less pronounced, whereas the mid-frequencies will seem louder.
a) A repetitive echo set up by parallel reflecting surfaces.
b) term used to refer to the fluctuations in speed of the platter of a record player when the speed increases.
Decreases in speed are referred to as “wow”
Monitor mix tailored to the needs of the performer
The number of times a signal vibrates each second as expressed in cycles per second (cps) or Hertz (Hz).The higher the frequency the higher the pitch.
Frequency Response
A graph showing how a microphone responds to various sound frequencies; It is a plot of electrical output (in decibels) vs. frequency (in Hertz).
The ratio of the signal level at the output of an audio device to the signal level at its input. Expressed in decibels (dB).
Short for “Go-Between”. A solid moveable acoustic barrier used to isolate sound sources.
The amount of room above an audio signal before distorting. The louder the sound, the less headroom it has. For example, if a sound is peaking at -5dB, it has 5dB’s of headroom.
Hypercardiod Microphone
A unidirectional microphone with tighter front pickup (105 deg.) than a supercardioid, but with more rear pickup
The input/output connections of a system.
IEM (In-Ear Monitor)
A foldback monitoring system, often used by musicians on stage with in-ear earpieces.
Inches Per Second. Used to describe tape speed
The provision on a mixing console or ‘channel strip’ processor of a facility to break into the signal path through the unit to insert an external processor. Budget devices generally use a single connection (usually a TRS socket) with unbalanced send and return signals on separate contacts, requiring a splitter or Y-cable to provide separate send (input to the external device) and return (output from external device) connections . High end units tend to provide separate balanced send and return connections.
Instrument Level
The nominal signal level generated by an electric instrument like a guitar, bass guitar or keyboard. Typically around -25dBu. Instrument signals must be amplified to raise them to line-level.
Isolation Room
A separate room or enclosure designed to provide acoustic isolation from external noise. Often used alongside a studio’s main live room to record vocals or drums, for example, without spill from other instruments.
Isopropyl Alcohol
A type of alcohol commonly used for cleaning and de-greasing tape machine heads and guides.
Jack Plug
A commonly used audio connector, usually ¼ inch in diameter and with either two terminals (tip and sleeve known as TS) or three (tip, ring, sleeve called TRS). The TS version can only carry unbalanced mono signals, and is often used for electric instruments (guitars, keyboards, etc). The TRS version is used for unbalanced stereo signals (eg for headphones) or balanced mono signals.
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 patchbay.
Jog Wheel
A hardware controller in the form of a rotary encoder which is often used to enable audio scrubbing in a DAW or audio editing platform.
An audio level metering format developed by mastering engineer Bob Katz which must be used with a monitoring system set up to a calibrated acoustic reference level. Three VU-like meter scales are provided, differing only in the displayed headroom margin. The K-20 scale is used for source recording and wide dynamic-range mixing/mastering, and affords a 20dB headroom margin. The K-14 scale allows 14dB of headroom and is intended for most pop music mixing/mastering, while the K-12 scale is intended for material with a more heavily restricted dynamic range, such as for broadcasting. In all cases, the meter’s zero mark is aligned with the acoustic reference level.
Light Emitting Diode. A form of solid state lamp.
Low Frequency Oscillator, often found in synths or effects using modulation.
The standard measurement of loudness, as used on Loudness Meters corresponding to the ITU-TR BS1770 specification. the acronym stands for ‘Loudness Units (relative to) Full Scale. Earlier versions of the specification used LKFS instead, and this label remains in use in America. The K refers to the ‘K-Weighting’ filter used in the signal measurement process.
The time delay experienced between a sound or control signal being generated and it being auditioned or taking effect, measured in milliseconds.
A rotating speaker used with Hammond B3 organs and electric guitars. As the speaker rotates, the Doppler effect comes into play such that as the speaker rotates toward the listener, the apparent tone of the instrument seems to rise slightly and the as it rotates away it decreases slightly. It is also accompanied by a slight raising and lowering of the apparent volume since at different points in time, the speaker is pointed some degree either toward or away from the listener.
An automatic gain-control device used to restrict the dynamic range of an audio signal. A Limiter is a form of compressor optimised to control brief, high level transients with a ratio greater than 10:1.
Line Level
A nominal signal level which is around -10dBV for semi-pro equipment and +4dBu for professional equipment.
A number of separate cables bound together for neatness and convenience. Also referred to as a “snake”.
Term used to describe perceived sound level. Sometimes erroneously referred to as “volume” (especially in domestic audio products) as volume is used to quantify a 3 dimensional space it is not suitable for describing sound pressure levels.
Loudness Wars
The practice of trying to make each new commercial music release sound subjectively louder than any previous release, on the misguided notion that louder is more exciting and results in more sales.
An electroacoustic transducer that changes electrical energy to acoustic energy, also simply called a speaker.
M-S (Mid-Side)
A specialist form of coincident microphone array which, when decoded to left-right stereo, creates an equivalent XY configuration. In the MS array one microphone is pointed directly forward (Mid) while the second is arranged at 90 degrees to point sideways (Side). The Mid microphone can employ any desired polar pattern, the choice strongly influencing the decoded stereo acceptance angle. The Side microphone must have a figure-eight response and be aligned such that the lobe with the same polarity as the Mid microphone faces towards the left of the sound stage. Adjusting the relative sensitivity of the Mid and Side microphones affects the decoded stereo acceptance angle and the polar patterns of the equivalent XY microphones.
Musical Instrument Digital Interface. A connecting specification that allows the communication and control of one device by another.
MTC (MIDI Time Code)
A format used for transmitting synchronisation instructions between electronic devices within the MIDI protocol.
Traditionally the sequencing of individual recordings to form a cohesive album of material, and to apply corrective equalisation and dynamics processing to ensure a consistent sound character and to optimise playback on the widest possible range of sound systems. Appropriate signal processing may also be applied to make the mastered material suitable for its intended medium (such as controlling transient peaks and dynamics and mono-ing the bass for vinyl records, etc).
A display intended to indicate the level of a sound signal. It could indicate peak levels (eg. PPMs or digital sample meters), average levels (VU or RMS meters), or perceived loudness (LUFS meters).
A transducer that takes an acoustic signal and converts into an electrical signal.
Loudspeakers used for critical sound auditioning purposes. Usually these loudspeakers have a flat or close to flat frequency response.
A single channel of audio.
One note at a time.
A synthesizer, sampler or module that can play several parts or different sounds at the same time, each under the control of a different MIDI channel.
A recording device capable of recording several ‘parallel’ parts or tracks which may then be mixed or re-recorded independently.
Nearfield Monitoring
Monitors used in mixing and mastering that are designed so that the listener is very close to the speakers. This allows the mixing or mastering engineer to listen at a lower volume and to hear more of the direct sound and less reflected sound from the walls and other surfaces.
A process carried out while a recording is not playing.
Omnidirectional Microphone
A microphone that picks up sound equally from all directions.
On/Off Axis
Directional microphones are inherently more sensitive to sound from one direction, and the direction of greatest sensitivity is referred to as the principle axis. Sound sources placed on this axis are said to be ‘on-axis’, while sound sources elsewhere are said to be ‘off-axis’
Open Reel
A tape machine where the tape is wound on spools rather than housed within a cassette. Also known as “reel to reel”.
Opto-electronic Device
A device where some electrical parameter changes in response to a variation in light intensity. For example, variable photo-resistors are sometimes used as gain control elements in compressors where the side-chain signal modulates the light intensity.
A circuit designed to generate a periodic electrical waveform.
Outboard Equipment 
Any signal processor that isn’t directly present in the DAW software or on the mixing console.
Recording new material to separate tracks while auditioning and playing in synchronism with previously recorded material.
Overheads –
Microphones, typically used when micing drum kits that are oriented about 3 feet or so above the cymbals. Can also be used to mic choirs, string sections or other acoustic ensembles. They are almost always used to produce a stereo image of what is being recorded
Pulse Code Modulation – the technique used by most digital audio systems to encode audio as binary data.
Pre-Fade Listen. A system used within a mixing console to allow the operator to audition a selected signal, regardless of the position of the fader controlling that signal.
PZM (Pressure Zone Microphone)
A type of boundary layer microphone.
A resistive circuit for reducing signal level.
Pan (Panorama)
The component on a mixer or in the recording software that allows the user to locate the track in the stereo or surround field.
Parameteric EQ
An equaliser with separate controls for frequency, bandwidth and cut/boost.
A circuit with no active elements.
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.
The maximum instantaneous level of a signal.
Phantom Power
A standardised professional method of providing power to the electronics of some types of microphones via a balanced XLR connection.
The relative position of a point within a cyclical signal, expressed in degrees where 360 degrees corresponds to one full cycle.
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.
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
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 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.
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’.
The ability of an instrument to play two or more notes simultaneously. An instrument which can only play one note at a time is described as monophonic.
Pop Shield
A device placed between a sound source and a microphone to trap wind blasts – such as those created by a vocalist’s plosives (Bs, Ps and so on) – which would otherwise cause loud popping noises as the microphone diaphragm is over- driven. Most are constructed from multiple layers of a fine wire or nylon mesh, although more modern designs tend to use open-cell foam. Also called a Pop Screen or Popper Stopper.
A gliding effect that allows a sound to change pitch at a gradual rate, rather than abruptly, when a new key is pressed or MIDI note sent.
A signal derived from the channel path of a mixer after the channel fader. A post-fade aux send level follows any channel fader changes. Normally used for feeding effects devices.
Work done to a recording, such as mixing or mastering. Sometimes called simply “post”.
Potentiometer (Pot)
A form of electrical potential divider in which the ratio of the upper and lower resistances can be changed either with a rotary control or slider (eg. a fader)
Power Amplifier
A device which accepts a standard line-level input signal and amplifies it to a condition in which it can drive a loudspeaker drive unit. The strength of amplification is denoted in terms of Watts of power.
Short for ‘pre-amplification’ : an active gain stage used to raise the signal level of a source to a nominal line level. For example, a microphone pre-amp.
An effects unit or synth patch that cannot be altered by the user.
The undesirable process that causes some magnetic information from a recorded analogue tape to become imprinted onto an adjacent layer. This can produce low level pre or post echoes.
A device designed to treat an audio signal by changing its dynamics or frequency content. Examples of processors include compressors, gates and equalisers.
Proximity Effect
Also known as ‘Bass tip-up’. The proximity effect dramatically increases a microphone’s sensitivity to low frequencies when placed very close to a sound source. It only affects directional microphones – omnidirectional microphones are immune.
The action of placing an already recorded track into record at the correct time during playback, so that the existing material may be extended or replaced.
The ‘quality-factor’ of a filter which defines its bandwidth and indicates a filter’s resonant properties. The higher the Q, the more resonant the filter and the narrower the range of frequencies that are allowed to pass.
Part of the process of digitising an analogue signal. Quantisation is the process of describing or measuring the amplitude of the analogue signal captured in each sample, and is defined by the wordlength used to describe the audio signal – eg. 16 bits.
Quantise (Function)
A means of moving notes recorded in a MIDI sequencer so that they line up with user defined subdivisions of a musical bar, for example, 16s. The facility may be used to correct timing errors, but over-quantization can remove the human feel from a performance.
An abbreviation for Random Access Memory. This is a type of memory used by computers for the temporary storage of programs and data, and all data is lost when the power is turned off. For that reason, work needs to be saved to disk if it is not to be lost.
Rack Mount
A standard equipment sizing format allowing products to be mounted between vertical rails in standardised equipment bays, 19″ Wide
An audio process that can be carried out as the signal is being recorded or played back. The opposite is off-line, where the signal is processed in non-real time.
Red Book CD
A term used to imply a standard audio CD. The name comes from the fact that the original specifications documents for the audio CD created by Sony and Philips had a red cover! Recordable CD-Rs are described as ‘orange book’ for similar reasons.
The way in which sound waves bounce off surfaces.
The time taken for a signal level or processor gain to return to normal. Often used to describe the rate at which a synthesized sound reduces in level after a key has been released. Also used to describe the time taken for a compressor top restore unity gain after a signal has fallen below the threshold. Also known as ‘recovery time .‘
The characteristic of a filter that allows it to selectively pass a narrow range of frequencies.
Short for Reverberation. The dense collection of echoes which bounce off acoustically reflective surfaces in response to direct sound arriving from a signal source. Reverberation can also be created artificially using various analogue or, more commonly, digital techniques.
Reverberation Time
The time taken for sound waves reflecting within a space to lose energy and become inaudible. A standard measurement is ‘RT60’ which is the time taken for the sound reflections to decay by 60dB.
Ribbon Microphone
A dynamic microphone where the sound capturing element is a thin metal ribbon diaphragm suspended within a magnetic field. When sound causes the ribbon to vibrate, a small electrical current is generated within the ribbon.
The rate at which a filter or equaliser attenuates a signal once it has passed the turnover frequency.
Room Modes
Acoustic resonances within an enclosed space or room. These occur at specific frequencies where the source sound is reflected from the room’s boundaries to reinforce and/or cancel with itself to create standing waves. This results in some areas in the room with very boomy or exaggerated pitches, and others where the pitch may be almost completely absent. The resonant frequencies involved relate directly to the sound wavelength and room dimensions, and is particularly prevalent at low frequencies.
Rotary Encoder
A hardware controller comprising a knob or dial which can be rotated in either direction without end-stops. A digital encoder of some kind attached to the shaft translates the movement into a digital code that can indicate both direction and speed of rotation to the controlling software of a device.
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.
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.
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.
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!
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.
Sawtooth Wave
So called because it resembles the teeth of a saw, this waveform contains both odd and even harmonics.
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.
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.
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 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.
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. Also known as Loom.
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.
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.
Square Wave
A symmetrical rectangular waveform. Square waves contain a series of odd harmonics.
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)
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.
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.
A specific type of efficient loudspeaker system intended to reproduce only the lowest frequencies (typically below 120Hz).
Sweet Spot
The optimum position for a microphone, or for a listener relative to monitor loudspeakers.
A system for making two or more pieces of equipment run in synchronism with each other.
The creation of artificial sound.
An electronic musical instrument designed to create a wide range of sounds, both imitative and abstract.
SysEx (System Exclusive)
A part of the MIDI standard that allows manufacturers to define their own specific message formats, commonly used to dump and load a specific product’s patch data.
A type of quarter-inch jack plug with three contacts (Tip, Ring and Sleeve), used either for stereo unbalanced connections (such as on headphones) or mono balanced connections (such as for line-level signals). Physically compatible in size with the TS (Tip, Sleeve) quarter-inch jack plug used for electric guitars and other instruments.
A system designed to enable voice communication between rooms.
The rate of the ‘beat’ of a piece of music measured in beats per minute.
Test Tone
A steady, fixed level tone recorded onto a multitrack recording, or passed over a signal connection to test the signal path and act as a reference when matching levels.
Referring to the tones that can be created by a synthesizer (see multi-timbral and bi-timbral)
The tonal ‘colour’ of a sound.
The term dates back to multitrack tape where the tracks are physical stripes of recorded material, located side by side along the length of the tape.
Triangle Wave
A symmetrical triangular shaped wave containing odd harmonics only, but with a lower harmonic content than the square wave.
see Valve
The colloquial term to describe a loudspeaker drive unit optimised for the reproduction of high frequencies. (See Woofer).
A 2-wire electrical signal connection where the signal conductor is surrounded by a screen which provides a 0V reference and also guards against electrical interference.
To play the same melody using two or more different instruments or voices.
Unity Gain
A condition where the output signal is the same amplitude as the input signal; the overall system gain is then x1 or unity.
Voltage Controlled Amplifier. An amplifier in which the gain (or attenuation) is controlled by an external DC voltage. VCA’s are used in a wide range of audio and musical equipment, such as fader-automation systems in large format mixing consoles, audio compressors, and synthesizers.
VCA Compressor
 VCA compressors tend to be fast-acting (at least in comparison to opto-compressors), a wide dynamic range, and low distortion.
VCA Group
Found in large mixing consoles. The fader levels of a number of separate channels assigned to the VCA group can be adjusted together by the VCA Group fader but without mixing their signals together. Usually referred to as a DCA Group in a digital console.
VU Meter
An audio meter designed to interpret signal levels in roughly the same way as the human ear, which responds more closely to the average levels of sounds rather than to the peak levels
Also known as a ‘tube’ in America. A thermionic device in which the current flowing between its anode and cathode terminals is controlled by the voltage applied to one or more control grid(s). Valves can be used as the active elements in amplifiers, and because the input impedance to the grid is extremely high they are ideal for use as an impedance converter in capacitor microphones. The modern solid-state equivalent is the Field Effect Transistor or FET.
Vari-Mu Compressor
An audio compressor that employs a valve (tube) as the variable audio attenuator. Mu is an engineering term for gain, so this is a variable-gain compressor. In essence, the side-chain signal continuously adjusts the bias o the valve to alter its gain appropriately. Vari-Mu compressors are fast and smooth, with low distortion.
The rate at which a key is depressed. This may be used to control loudness (to simulate the response of instruments such as pianos) or other parameters on later synthesizers.
Pitch modulation using an LFO to modulate a VCO
Vocal Booth
See Isolation Room
A signal processor that imposes a changing spectral filter on a sound based on the frequency characteristics of a second sound. By taking the spectral content of a human voice and imposing it on a musical instrument, talking instrument effects can be created.
The capacity of a synthesizer to play a single musical note. An instrument capable of playing 16 simultaneous notes is said to be a 16-voice instrument.
Wah Pedal — Wah-Wah
A guitar effects device where a bandpass filter is varied in frequency by means of a pedal control.
A subjective term used to describe sound, where the bass and low-mid frequencies have depth and where the high frequencies are smooth-sounding rather than being aggressive or fatiguing. Warm-sounding tube (valve) equipment may also exhibit some of the aspects of compression.
Watt (W)
Unit of electrical power named after its founder, James Watt.
A graphic representation of the way in which a sound wave or electrical wave varies with time.
A signal that has effects added
White Noise
A random signal with a flat (constant) power spectrum density, ie. equal power within any frequency band of fixed width. White noise sounds very bright
Word Clock
The precise timing of digital audio samples is critical to the correct operation of interconnected digital audio equipment. 
Wow & Flutter
A cyclical variation in replay speed which affects the pitch of the recorded material. Wow is a low-speed variation (nominally below 4Hz) which typically occurs once per revolution of the device and may be caused by an off-centre hole on a vinyl record, or a sticking tape on a reel-reel machine. Flutter is a higher speed variation (nomninally above 4Hz) and can often be perceived as a form of intermodulation distortion.
A specific way of mounting two directional microphone capsules such that they both receive sound waves from any direction at exactly the same time. Information about the direction of a sound source is captured in the form of level differences between the two capsule outputs. Commonly, the two microphones in an X-Y array are mounted with a mutual angle of 90 degrees, although other angles are sometimes used. The two capsules will have the same polar pattern, the choice of which determines the stereo recording angle (SRA). The X-Y configuration is entirely mono-compatible because there are no timing differences between the two channels.
A very robust and latching connector commonly used to carry balanced audio signals such as the outputs from microphones or line-level devices. Standard balanced audio interfaces — analogue and digital — use three-pin XLRs with the screen on pin 1, the ‘hot’ signal on pin 2 and the ‘cold’ signal on pin 3.
A form of adapter cable that passively splits the output of a source to feed two or more destinations. Y-leads may also be used in unbalanced console insert points, in which case a stereo jack plug at one end of the lead is split into two monos at the other for separate send and return connections. A Y-lead must never be used to combine signals.
The parameter of tape head alignment relating to vertical alignment head and whether it is leaning forward or back relative to the tape path
Zero Crossing Point
The point at which a signal waveform crosses from being positive to negative or vice versa.