Any grouping of electronic equipment intended for sound synthesis. Such equipment usually incorporates a combination of oscillators, filters, mixers, envelope generators, white noise generators, switches, reverberation units, etc. The term is now generally applied to digital sound synthesizers as well as their analogue antecedents.
All analogue synthesizers 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. The abbreviations VCO, VCA and VCF are used to describe voltage-controlled oscillators, amplifiers and filters, respectively.
Digital synthesizers utilise techniques of digital sound synthesis, ranging from those which implement specific synthesis algorithms, to those (called samplers) based on reproducing digitally sampled sounds, to those which are programmable and therefore can implement a variety of digital signal processing (DSP) techniques. Increasingly, however, stand-alone hardware digital synthesizers (other than keyboards and the like) are being replaced by systems implemented in software on general-purpose computers. (Source - Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)