Two synths can start from the same oscillator and sound completely different. What sets them apart, often, is not the raw sound but its shape over time: how the note appears, holds, then dies. That aspect is handled by the envelope, and its most common form has a name everyone runs into sooner or later: ADSR, for Attack, Decay, Sustain, Release. Understanding these four parameters means holding one of the most expressive levers in synthesis — at least as much as the choice of waveforms in subtractive synthesis.
What is an envelope for?
An oscillator left to itself produces a continuous, unchanging sound. But no real sound behaves that way: a plucked string starts loud and decays, an organ tone settles and holds as long as you press, a mallet hit cracks then dies. The envelope is the generator that reproduces this profile: it puts out a control voltage that rises and falls over time, and that voltage drives a parameter — most often volume, but just as easily filter cutoff or pitch.
The trigger is the note: on a keyboard, pressing a key starts the envelope (the gate opens), releasing the key ends it (the gate closes). On a modular, a gate or trigger signal plays that role, exactly the logic described in our article on MIDI and CV/Gate.
The four stages, one by one
Three of the four controls are times; only one, sustain, is a level. That is the key to never mixing them up again.
- Attack — the time the sound takes to go from zero to its maximum, the moment the note is played. Very short attack: the sound snaps, percussive. Long attack: it swells in, like a pad opening up.
- Decay — the time the sound takes to fall from the peak down to the sustain level, once the peak is reached. This is what gives the “pluck” of a note that snaps then settles.
- Sustain — careful, this is not a time but a level: the one the sound holds at while you keep the key down. Sustain at full: the sound holds at full power. Sustain at zero: the sound disappears after the decay, even if you hold the note — that is how you get a percussion or a pluck.
- Release — the time the sound takes to fall back to zero after you let go of the key. Short release: the note cuts off cleanly. Long release: it lingers, rings, melts into the next.
The musical gesture reads in that order: you press (attack then decay down to sustain), you hold (sustain), you release (release). Once you read it that way, setting an envelope becomes a direct conversation with the sound.
Volume, filter, pitch: one envelope, three destinations
Most synths offer at least two envelopes. The first almost always drives amplitude (volume): it sets the overall contour. The second is usually routed to the filter, and that is where synthesis comes alive. A filter envelope with a fast attack and a medium decay produces that “wah” that opens then closes the timbre on every note — the signature of countless acid basses and biting leads. Routing an envelope to pitch, finally, creates percussive pitch effects, widely used for electronic toms or kicks that “drop.”
So the same ADSR profile does not produce a single result: it all depends on what it controls. That is what makes the tool so central to sound design, from the most classic synth to the engine of a sampler, where the envelope shapes sample playback.
Three examples to practice on
| Target sound | Attack | Decay | Sustain | Release |
|---|---|---|---|---|
| Pluck / percussion | very short | short to medium | zero | short |
| Pad | long | any | high | long |
| Organ / held tone | short | short | maximum | short |
These three settings cover most of the repertoire. A pluck is a sustain at zero: the sound snaps then dies without the key having to be released. A pad is the opposite: long attack and release, high sustain, for a sound that settles and melts into the mix. Between the two, it is all a matter of degree.
Beyond ADSR
ADSR is only a convention, the most common one, not a law. Some synths simplify to AD or AR; others offer envelopes with more stages (DADSR with a delay, fully drawable multi-segment envelopes) or curves adjustable between linear and exponential, which changes the “feel” of the same attack a lot. On the most modern instruments, an envelope can modulate almost any parameter, from the FM modulation amount to a grain’s read position in granular synthesis. The principle does not budge: a shape over time, triggered by a note, sent to a destination. And that shape often comes to life inside a step sequencer, where every note retriggers the envelope.
My take
ADSR is the first real click in synthesis: the moment you stop turning knobs at random and start hearing why a sound snaps or lingers. The best exercise is still to take a flat organ patch and turn it into a pluck, then a pad, using nothing but the four sliders — in a minute, the ear grasps what ten pages of manual never explain. The classic trap is not really a trap, it is a pleasure: you spend hours fine-tuning a filter envelope. Good. That is exactly where a synth’s character lives.
