Envelopes are built from named segments; sustain level is set by the designer but its duration by the performer

Envelopes are assembled from time/level segments (ramps): Delay (time from note-on to the start of attack), Attack (rise from minimum to maximum), Hold (plateau at maximum), Decay (fall from peak to sustain level), Sustain (a constant level held until note-off), and Release (fall from the current value to zero). Each segment except Sustain is a fixed, designer-controlled duration. Sustain is special: the designer sets its LEVEL, but its DURATION is controlled by the performer — it lasts exactly as long as the key is held. Classic ADSR uses only Attack, Decay, Sustain, Release; other envelopes add or drop segments.

Examples

ADSR on a pad: long attack (2s), short decay (100ms), high sustain (90%), long release (3s) swells in and hangs. A percussive hit: near-zero attack, short decay, zero sustain — sharp transient only, sustain duration irrelevant.

Assessment

Name the one segment whose duration is controlled by the performer rather than the designer, and state what the designer sets for it instead.