What it changes in the music
Sustain is generally a level parameter rather than a duration. At zero sustain, a held note can fade away after the decay stage. A higher value preserves more continuing body. Different instruments may implement envelope behavior differently, so test the patch with both held notes and the actual phrase. The interaction with note length can change its practical role.
A small experiment
Keep attack and decay fixed, hold a note and move sustain from low to high. Listen to the portion after the initial accent rather than the onset itself.
Keep this distinction clear
Sustain level does not specify how long you hold the note. Note duration, pedal behavior and the release stage contribute separately to when the sound finally ends.
Related sound terms
Technical background
- Ableton Learning Synths — Interactive synthesis fundamentals.
- MDN: OscillatorNode — Waveform and oscillator behavior in Web Audio.
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