ADSR Explained: Attack, Decay, Sustain, Release (With Settings)

ADSR stands for attack, decay, sustain and release, the four stages of the envelope that shapes a synth note from the moment you press a key until it goes silent. Attack is how fast the note reaches full volume, decay is how fast it falls to the sustain level, sustain is the level it holds while your finger stays down, and release is how long it takes to fade after you let go. Three of the four are times and one is a level, and together they decide whether one saw wave comes out as a pluck, a pad or a tight bass.

How an ADSR envelope works

An ADSR envelope is a shape the synth draws once for every note. Pressing a key opens a gate and starts the attack; the envelope runs through the decay and parks at the sustain level for as long as the gate stays open. Letting go closes the gate and starts the release. The one on volume is the amp envelope; panels often label envelopes EG, for envelope generator.

Here is one note, held for two seconds:

The note lasts 2.5 seconds in all. Hold the key for four seconds and it lasts 4.5, because only the sustain stage stretches.

In 1965, after discussions with Vladimir Ussachevsky, head of the Columbia-Princeton Electronic Music Center, Robert Moog built an envelope module with four settings labeled T1, T2, ESUS and T3. ARP later renamed them attack, decay, sustain and release. Units vary (milliseconds on some synths, 0 to 127 on others), so treat every number here as a starting point. Some envelopes add a hold stage at the peak (AHDSR), and drums often get by with attack and decay alone (AD).

Attack and decay: how a note starts and settles

What attack does

Attack is the time from pressing the key to the peak of the envelope. Your ear leans on those first milliseconds to tell a plucked string from a bowed one.

• 0 to 5 ms: an instant start. Basses, plucks, drums, organs and most keys.
• 5 to 50 ms: a softer front edge, like a flute or a breathy lead.
• 50 to 200 ms: a short swell, like a brass player filling the horn.
• 200 ms to 2 s: a slow fade-in for pads, strings and drones.

A 0 ms attack can click at the start of every note, because the wave jumps from silence to full level in one step; 1 to 3 ms cures the click without softening the hit. A slow attack also makes notes arrive late. At 120 BPM an eighth note lasts 250 ms, so eighth notes through a 300 ms attack never reach full volume and drag behind the beat. Keep attack under about 20 ms for fast parts.

What decay does

Decay is the time the envelope takes to fall from its peak to the sustain level. What you hear depends on where sustain sits:

• Sustain at 100 percent: decay has nothing to do, because the peak and the sustain level are the same. If the decay knob seems dead, check sustain first.
• Sustain at 0: decay becomes the length of the whole note. Plucks, pianos, bells and drums work this way.
• Sustain in between: the note jumps above its held level for an instant, then settles. That small bump is what makes a bass or a clav feel punchy.

Sustain vs release: the pair beginners mix up

Sustain is a level and release is a time. The classic mistake is turning up sustain to make notes ring on after you let go. That ring is release; sustain only counts while a key is down.

The piano adds to the confusion. A piano note fades while you hold the key (zero sustain and a long decay, in synth terms), and its sustain pedal, which keeps notes ringing after you let go, acts more like a long release. A synth’s sustain pedal holds the gate open, so the release starts when your foot comes up.

Release starts from whatever level the envelope has reached when you let go, which is not always the sustain level:

• On a pad with a one-second attack, a 200 ms tap lets go long before full volume, so short taps come out quiet.
• On a pluck with zero sustain, letting go early hands the note to the release, so a release much shorter than the decay chops quick taps off. Set release close to decay, as in the guide to making a pluck synth, and a tap rings as long as a held note.

Under about 5 ms, release can click at the end of a note. Between 20 and 80 ms it is tight and clean, right for basses, organs and quick leads. At 1.5 to 3 seconds each chord hangs under the next, which is lovely on pads and bells and a mess on a moving bass line.

ADSR settings for bass, pads, plucks, leads and keys

Load an init patch (a blank sound with every control at its default), play a single saw wave, and try these amp envelopes.

For bass, a 40 to 80 ms release stops each note before the next one lands, leaving room for the kick drum. Full sustain gives a sub even notes; dropping sustain to 50 or 60 percent adds the punch. If the bass clicks, raise the attack to 3 to 5 ms. On a mono synth, legato (single-trigger) mode stops overlapping notes from restarting the envelope, which suits slides and robs a driving line of its punch. The 808 bass uses zero sustain, a long decay and a pitch drop; the synth bass recipes cover it.

For pads, keep the attack shorter than the time between chord changes. At 90 BPM a bar of 4/4 lasts about 2.7 seconds, so an 800 ms attack finishes its swell with nearly two seconds to spare. Change chords every two beats (about 1.3 seconds) and a 2-second attack never lets a chord reach full volume before the next one starts.

To copy an envelope from a sound you like, play one long note and listen in order:

1. The start. A hard hit means an attack under 5 ms; an audible swell means 50 ms or more.
2. The held part. If the note fades while the key is down, sustain is low and decay sets the length.
3. The level a held note settles at (sustain), then the tail after you let go (release).

Practice on the free online chord player by holding one chord on each of its three sounds: the Pad swells in and hangs on after you let go, the Pluck hits at once and fades even while you hold it, and Keys starts bright and turns rounder as it rings.

Beyond volume: envelopes on the filter, FM and pitch

Many synths have a second envelope for other targets, with an amount knob that sets how far it pushes that control from where you set it.

Filter envelope. Aimed at the cutoff frequency, an envelope changes each note’s brightness over time. For the classic “bwow” bass, set the cutoff low (around 300 Hz), turn the envelope amount most of the way up, and give the filter envelope a 0 ms attack, a 200 ms decay and zero sustain while the amp envelope stays at full sustain. The volume holds and the tone closes. For brass, a 50 to 80 ms filter attack makes the brightness swell along with the volume. For plucks, make the filter decay shorter than the amp decay, so each note goes dark before it goes quiet.

FM envelope. In FM synthesis the modulator’s level sets the brightness, so an envelope on it gives each note a bright, clangy strike and a purer tail, the sound of FM electric pianos and bells. The Yamaha DX7 (1983) gives each of its six operators its own envelope, built from four rates and four levels, plus a seventh envelope for pitch. FM synthesis explained simply shows how ratio and amount work together.

Pitch envelope. A fast pitch drop turns a sine wave into a drum: one or two octaves over 30 to 60 ms gives a kick, and a smaller drop with a longer amp decay gives a tom. Stretch the drop across several octaves and a few hundred milliseconds for a laser zap.

In Gelato Synth, our synth for iPhone, the Env page shows the envelope curve with four upright faders for Attack, Decay, Sustain and Release (attack goes down to 0.5 ms), plus Punch, a fast pitch drop for kicks, toms and zaps. Envelope to filter on the Filter page and Envelope to FM on the FM page add the brightness moves above.

On any synth, set the amp envelope first, since every other envelope works inside it: a filter release longer than the amp release changes nothing you can hear.