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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 form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies at high sound pressure levels (notionally 100 Phons or about 87dBA SPL). Essentially, the filter rolls-off the low frequencies below about 20Hz and the highs above about 10kHz. This filtering is often used when making measurements of high-level sounds, such as when calibrating loudspeaker reference levels. (See also A-Weighting and K-Weighting.)


The physical construction which encloses and supports the loudspeaker drive units. Usually built of wood or wood-composites (although other materials are often used including metal alloys and mineral composites). Cabinets can be ‘sealed’ (often referred to, misleadingly, as an 'infinite baffle') or ‘vented’ in various ways (ported, bass-reflex, ATL, transmission line), the precise design influencing the bass and time-domain characteristics.

Cabinet Resonance

Any box-like construction will resonate at one or more frequencies. In the case of a loudspeaker, such resonances are likely to be undesirable as they may obscure or interfere with the wanted sound from the drive units. As resonance also involves the storing and releaseing of energy over time, cabinet resonances can result in 'time smearing', causing a sharp impulsive sound like a 'thud' to be reproduced as a prolonged 'boom'.  Cabinets are usually braced and damped internally to minimise resonances.


A passive, two-terminal electrical component which stores energy in the form of an electrostatic field. The terminals are attached to conductive ‘plates’ which are separated by a non-conductive dielectric. Capacitance is measured in Farads and the amount of capacitance depends upon the size of the plates and the spacing between them.  If a voltage is applied across the terminals of a capacitor a static electric field develops across the dielectric, with positive charge collecting on one plate and negative charge on the other. Where the applied voltage is an alternating signal, a capacitor can be thought of as a form of AC resistance that reduces with increasing signal frequency. The old-fashioned term is a ‘condensor’.

Capacitor Microphone

Also known as a 'condenser microphone'. This is a specific form of electrostatic microphone which operates on the principle of measuring the change in electrical voltage across a capacitor which contains a constant static charge. The capacitor is formed from two metal electrodes, one fixed (the back-plate) and the other a thin conductive membrane that flexes in response to sound pressure, and the static charge comes either from a DC-bias voltage or a dielectric material. (See also 'Back Electret', and 'RF Capacitor Microphone'.)


An alternative term for a transducer which converts acoustic sound waves into an electrical signal.

Carbon Microphone

(Also known as a Carbon Button Microphone). An obsolete form of microphone in which carbon granules are contained between two metal contact plates, one of which acts as the diaphragm and moves in response to sound waves. The microphone has to be biased with a DC voltage which causes a current to pass from one metal contact plate, through the carbon granules, to the other metal contact plate. The varying pressure exerted on the carbon granules by the moving diaphgram causes a varying resistance and thus a varying current which is analogous to the sound waves. Carbon Button Microphones were used in the very early days of sound recording and broadcasting, as well as in domestic telephones up until the 1980s when electret capsules became more commonplace.


A specific form of polar response of a unidirectional microphone or loudspeaker. It is an inverted heart-shape which has very low sensitivity at the back (180 degrees), but only slightly reduced sensitivity (typically between 3 and 6dB) at the sides (90/270 degrees).


A recordable type of Compact Disc that can only be recorded once and it can't be erased or reused. The CD-R’s technical characteristics are defined in the ‘Orange Book’

CD-R Burner

A device capable of recording data onto blank CD-R discs.

Chamber Reverb

A term widely used in artifical reverb systems to describe a reverberant space with a specific sonic character. Typically, a chamber reverb is generous and dense, but usually with greater focus and clarity, and less duration, than a Hall reverb. Histortically, a physical reverb chamber was a moderate sized room with tiled surfaces and often glazed pipes stood on end to increase the reverb density, in which one or more loudspeakers reproduced sounds which were picked up by one or more distant microphones.


A path carrying audio or data. In the context of a mixing console a channel is a single strip of controls relating to one input. In the context of MIDI, Channel refers to one of 16 possible data channels over which MIDI data may be sent. The organisation of data by channels means that up to 16 different MIDI instruments or parts may be addressed using a single cable.

Characteristic Impedance

If a cable is long relative to the wavelength of the signal it is conveying it is said to behave as a 'transmission line' and the signal is passed as an eletromagnetic wave along the cable. In this condition, the cable itself has a 'characteristic impedance' which can be thought of as the impedance measured at the input if the cable is infinitely long, and it depends on the cable construction — the materials and their geometries — rather than the length. It is necesary to terminate each end of a transmission line with the same impedance as its characteristic impedance. if this is not done the propagating wave will be reflected from the ends of the cable, and the reflected energy can interfere with the source signals.

The characteristic impedance of typical coaxial video and S/PDIF digital cables is 75 Ohms, while AES3 and RJ45 Ethernet cables is around 110 Ohms.


A term describing the process whereby a follower device attempts to synchronise itself with a master device. In the context of a MIDI sequence, Chase may also involve chasing events - looking back to earlier positions in the song to see if there are any program change or other events that need to be acted upon.


A slang term for an Integrated Circuit or IC.


Three or more different musical notes played at the same time.


An effect created by doubling a signal and adding delay and pitch modulation, intended to make a single source sound more like an ensemble.


A scale of pitches rising or falling in semitone steps.

Class-A / AB / D / G

Different electronic amplifier circuit topologies are identified as different classes. It's a topic that takes quite a lot of explanation, but a full desciption can be found here.

Click Track

An audible metronome pulse which assists musicians in playing in time.


When an audio signal is allowed to overload the system conveying it, clipping is said to have occurred and severe distortion results. The ‘clipping point’ is reached when the audio system can no longer accommodate the signal amplitude –either because an analogue signal voltage nears or exceeds the circuitry’s power supply voltage, or because a digital sample amplitude exceeds the quantiser’s number range. In both cases, the result is that the signal peaks are ‘clipped’ because the system can’t support the peak excursions - a sinewave source signal becomes more like a squarewave. In an analogue system clipping produces strong harmonic distortion artefacts at frequencies above the fundamental. In a digital system those high frequency harmonics cause aliasing which results in anharmonic distortion where the distortion artefacts reproduce at frequencies below the source fundamental. This is why digital clipping sounds so unlike analogue clipping, and is far more unpleasant and less musical.


The process of controlling the sample rate of one digital device with an external clock signal derived from another device. In a conventional digital system there must be only one master clock device, with everything else ‘clocked’ or ‘slaved’ from that master.


An exact duplicate. Often refers to digital copies of digital tapes.


A mic technique which involves placing a microphone very close to a sound source, normally with the intention of maximising the wanted sound and minimising any unwanted sound from other nearby sound sources or the room acoustics. In classic music circles the technique is more often known as 'Accent Miking'.


Essentially an internet communications network (either a Wide Area Network [WAN] or a private network) in which a data-centre performs a range of services such as data storage (cloud storage) or remote apps and programs (cloud computing). The term comes from the way network engineers used to draw system diagrams with a cloud symbol to simplify a very complex (and irrelevant) network of routers, switches, drives and cables into something that just showed the relevant external connection points.


An abbreviation formed from coder-decoder, implying a 'double-ended' processing system where a signal is encoded into a specific format before transmission or recording, and then decoded on reception or replay. An example of an analogue codec might be the Dolby A or Dolby B tape noise-reduction systems, while a digital codec might be something like the FLAC data-reduction system where redundant data is removed in the coding process and fully restored in the decoding process.


A means of arranging two or more directional microphone capsules such that they receive sound waves from all directions at exactly the same time. The varying sensitivity to sound arriving from different directions due to the directional polar patterns means that information about the directions of sound sources is captured in the form of level differences between the capsule outputs. Specific forms of coincident microphones include ‘XY’ and ‘MS’ configurations, as well as B-format and Ambisonic arrays. Coincident arrays are entirely mono-compatible because there are no timing differences between channels.


A distortion of the natural timbre or frequency response of sound, usually but not always unwanted.


A series of deep filter notches created when a signal is combined with a delayed version of itself. The delay time (typically less than 10ms) determines the lowest frequency at which the filter notches start.

Common Mode Rejection

A measure of how well a balanced circuit rejects an interference signal that is common to both sides of the balanced connection.

Compact Cassette

Originally conceived as a recording format for dictation machines in the early 1960s, it became a mainstream music release format in the form of the Musicassette. A plastic shell protected 3.81mm wide (1/8-inch) recording tape which ran at 4.75cm/s. A stereo track was recorded in one direction, and the tape could be turned over to play a second stereo track recorded in the opposite direction.


An encode-decode device typically employed to pass a wide dynamic range signal over a channel with a lower dynamic range capability. The source signal is compressed in the encoder to reduce the dynamic range, and subsequently expanded by the decoder to restore the original dynamics. The Dolby noise reduction codecs are examples of companders.

Compression Driver

A type of loudspeaker designed to feed sound into an acoustic horn, or flared opening. A compression driver is designed to work in a 'compression mode', where the air immediately in front of the transducer diaphragm is constrained by the throat of the horn to create a high acoustic impedance. The horn acts as an acoustic transformer to couple the high impedance area in front of the driver to the low impedance of the atmosphere, optimising the power transfer and increasing efficiency significantly.


A device (analogue or digital) which is designed to reduce the overall dynamic range of an audio signal either by attenuating the signal if it exceeds a set threshold level according, or by increasing the level of quiet signals below a threshold. The amount of attenuation is defined by a set ratio, while the speed of response (attack) and recovery (release) can usually also be controlled.


A device which can be instructed (or programmed) to carry out arithmetic or logical operations. Although mechanical 'analogue' computers do exist, most are now electronic and digital, and process digital data.