What it changes in the music
Decay contributes to the difference between an initial accent and the continuing body. With sustain at zero, the sound can fade while the note is held. With higher sustain, a similar decay leaves a stable remaining level. A filter envelope can also use decay to soften the spectrum after an initial opening. Judge the destination, not just the knob name.
A small experiment
Hold one note with low sustain and vary decay. Then raise sustain without changing decay and listen for the continuing body underneath the onset.
Keep this distinction clear
Envelope decay is distinct from release after note-off and from a reverb’s decay-time control. They describe different parts of the signal path.
Related sound terms
Technical background
- Ableton Learning Synths — Interactive synthesis fundamentals.
- MDN: OscillatorNode — Waveform and oscillator behavior in Web Audio.
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