West Coast systems favour two-stage AD or AR slope generators over four-stage ADSRs

An ADSR envelope has four settable stages (Attack, Decay, Sustain, Release). West Coast systems favour simpler two-stage generators: AD (Attack-Decay) fires a rise-then-fall shape from a trigger with no sustain; AR (Attack-Release) rises and holds while the gate is held, then falls on release. These are often called slope or function generators. Their simplicity suits the percussive, non-keyboard-gated textures common in West Coast patching, and when their end-of-cycle output is looped back to their trigger they double as LFOs or oscillators. Where no sustain is needed, the ADSR’s sustain parameter is simply irrelevant.

Examples

An AD generator with a 2 ms attack and 80 ms decay, triggered on the beat, gives a tight percussive envelope for LPG plucks. Patch its end-of-cycle output to its own trigger input and it free-runs as an LFO.

Assessment

Give two musical situations where an AD generator is preferable to an ADSR, and one where the ADSR’s sustain stage is essential. What happens when an AD generator’s end-of-cycle output is fed back to its trigger?