ADSR envelope: attack, decay, sustain and release explained
An ADSR envelope shapes how a synth note changes over time: how fast it rises, how far it falls, the level it holds while you hold the key, and how long it fades after you let go. Here is what each stage does and settings for plucks, pads, basses and leads.
An envelope describes how a sound changes over time. On a synth, the ADSR envelope shapes each note from the moment you press a key to the moment it fades out after you let go. Most often it controls volume, but the same shape can move a filter's cutoff or the pitch.
The four stages
- Attack: the time for the level to rise from nothing to its peak after you press the key. A short attack gives a sharp start; a long one fades the note in.
- Decay: the time for the level to fall from the peak to the sustain level.
- Sustain: the level held for as long as the key stays down. It is a level, not a time.
- Release: the time for the level to fall to nothing after you let go of the key.
A piano shows the idea: its note starts almost at once and then fades away, even if you keep the key down, which on a synth is a fast attack, a long decay and a sustain at zero.
Where ADSR came from
Robert Moog built the envelope generator in the 1960s at the suggestion of the composer Herbert Deutsch. In 1965, after discussions with the composer Vladimir Ussachevsky, he built a new envelope module with four controls named T1, T2, ESUS and T3; ARP later simplified them into the ADSR form most synths use today. Some synths add stages, such as a delay before the attack starts, or a hold that keeps the level at its peak for a set time, as Kiln's DLY and HLD do.
Envelope settings to start from
| Sound | Shape |
|---|---|
| Pluck | Fast attack, short decay, sustain at zero, short release |
| Pad | Slow attack, high sustain, long release |
| Bass | Fast attack, high sustain, short release so notes stay tight |
| Lead | Fast attack, high sustain, medium release |
These are shapes to start from, not rules: a slow attack on a bass or a long release on a pluck can be exactly the sound you want.
Envelopes beyond volume
Route an envelope to a filter's cutoff and each note gets brighter on the attack and darker as it decays, a common way to shape plucks and basses. Route one to pitch for a quick drop at the start of each note, like Kiln's Knock, a pitch sweep into each note that many of its basses use. Most synths give the filter or pitch its own envelope, separate from the volume envelope.
Envelopes in Kiln
Kiln Synthesizer has four envelopes on its Motion page. ENV 1 shapes each note's volume; ENV 2 to ENV 4 do nothing until you route them in the modulation matrix. Each has DLY (a wait before the attack), ATK, HLD (time held at the peak), DEC, SUS and REL, plus attack and decay curves and a velocity amount. On Kiln's new 1.0 basses and leads, the Punch and Pluck macros shorten the amp envelope for you. The Kiln manual lists every range.
Questions
What does ADSR stand for?
Attack, decay, sustain and release, the four stages of the envelope.
What is the difference between decay and release?
Decay happens while the key is still down, falling from the peak to the sustain level. Release happens after you let go, falling from wherever the level is to nothing.
Why does my synth note click at the start or end?
An attack or release of zero can start or stop the sound abruptly. Lengthen either by a few milliseconds.
