A grouping of electronic modules intended for sound processing. Such equipment usually incorporates a combination of oscillators (tone generators), filters, mixers, envelope generators, noise generators, reverberation units, etc. The term is now generally applied to digital sound synthesizers as well as their analogue antecedents. All analogue synthesisers use the principle of voltage control to determine the values of the various sound parameters.

Sequences of control voltages may be produced by a keyboard or by a sequencer where the voltages are pre-set and then generated in a fixed sequence. Digital synthesisers utilise techniques of digital sound synthesis using one of a variety of digital sound processing (DSP) techniques. Increasingly non-keyboard based synthesisers are being replaced by software-based systems on personal computers. [Truax, EARS]