see Capacitor Microphone

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.

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.

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.

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.

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

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.

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

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.

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.