The same note can be a plucked string or a swelling pad — the pitch is identical, only its LOUDNESS over time differs. Attack, Decay, Sustain, Release: four numbers that turn one oscillator into a whole orchestra. Slide pluck → pad and ▶ play the shape.
The ADSR amplitude envelope. Four stages shape a note's loudness: ATTACK (rise to peak), DECAY (fall to the sustain level), SUSTAIN (held level while the key is down), RELEASE (fade after key-up). The same 440 Hz oscillator becomes a percussive pluck (fast attack, no sustain) or a slow pad (long attack, high sustain) purely by these numbers — timbre in time, not in pitch. The slider morphs between a pluck and a pad; a fail-loud self-check throws unless the envelope is continuous, the sustain level stays in [0,1], and the pluck's attack is shorter than the pad's. Press ▶ to hear the current shape on a fixed pitch.
A four-segment linear envelope on a pure sine; real instruments layer several time-varying envelopes (amplitude, filter, pitch). The envelope shape and its play-out are computed exactly.