Synthesis · glossary
ADSR
Also called ADSR envelope, envelope, attack decay sustain release, amp envelope
ADSR is the four-stage envelope that shapes a synth note over time: Attack (how fast it rises), Decay (how fast it falls to the sustain level), Sustain (the level held while the key is down) and Release (how long it fades after you let go).
An envelope is a shape a synth plays out once every time you press a note. ADSR names its four stages. Three of them are times and one is a level:
- Attack: the time from silence to full level after you press. Near 0 ms the note starts instantly; 1 to 2 seconds makes it swell in.
- Decay: the time to fall from that peak to the sustain level.
- Sustain: the level the note holds for as long as your finger stays down.
- Release: the time to fade to silence after you let go.
On volume, where it is called the amp envelope, these four settings alone can make the same saw wave play like any of these:
| Sound | Attack | Decay | Sustain | Release |
|---|---|---|---|---|
| Organ | 2 ms | any | 100% | 20 ms |
| Pluck | 1 ms | 200 ms | 0% | 150 ms |
| Punchy bass | 1 ms | 150 ms | 60% | 50 ms |
| Pad | 800 ms | 1 s | 80% | 2 s |
Sustain changes what decay does. With sustain at 100% the decay knob has nothing to do; with sustain at 0% the decay becomes the length of the whole note, which is how plucks, bells and drums work.
Send an envelope to a filter’s cutoff frequency and it shapes brightness instead of volume: a fast decay makes each note start bright and close down, the core of plucks and snappy basses. On FM synths, an envelope on the FM amount does the same job.
You meet ADSR on almost every synth and sampler, usually drawn as a line that rises, dips, holds flat and falls. In Gelato Synth, the Env page shows that curve with four upright faders for Attack, Decay, Sustain and Release, and attack goes down to 0.5 ms. ADSR explained has settings for more sounds, and making a pluck synth puts a short envelope to work.
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