Sample and Hold

A circuit or function in early synthesizers that enables the instantaneous value (voltage) of a waveform to be captured, and continues to output that value until the next sample is taken. This voltage is then used to control some other parameter in the synth such as a filter. Depending on how they are used, a sample and hold circuit can produce pretty random sounding fluctuations in one or more aspects of a sound. A good example of sample and hold applied to filter cutoff is at the beginning of the Emerson Lake and Palmer classic, Karn Evil 9.