A voltage-controlled amplifier driven by an envelope generator shapes a sound's loudness over time

A voltage-controlled amplifier (VCA) — Buchla’s Model 110 ‘voltage controlled gate’ — passes an audio signal at a gain set by an applied control voltage. On its own it is just a level control; the musical work happens when its control input is fed by an attack/envelope generator (Model 180), which produces a time-varying voltage (attack, then decay/duration). The VCA then imprints that contour onto the audio, turning a steady tone into a note with a beginning, body, and end. This VCA-plus-envelope pairing is how loudness dynamics are created in a modular synth; the same shape, applied elsewhere, becomes vibrato or filter sweeps.

Examples

Model 110 gates are ‘generally used in conjunction with a Model 180 attack generator to control the envelope of applied signals.’ Model 180 sets attack (.002–1 s), decay, and duration.

Assessment

Explain the roles of the VCA and the envelope generator in producing an amplitude envelope, and what you would hear from the VCA alone with no envelope patched in.