How ADSR Envelopes Shape Sound

An envelope describes how a sound changes over the life of a note. Almost every synthesizer uses some version of the ADSR envelope, which has four stages: attack, decay, sustain and release. Together they answer the questions a player cannot avoid. How fast does the sound arrive? How quickly does it fall? How loud does it stay while the key is held? What happens after the key is released?

This guide goes deeper than a quick definition. It explains how each stage behaves, how curve shape changes the feel, and how to choose starting values for common sounds. Pair it with the subtractive synthesis article, because the same envelope can control loudness, filter cutoff or pitch.

What an envelope is

An envelope is a control signal that starts when a note begins and changes over time. It does not make sound by itself. Instead, it moves another parameter, most often the amplifier level, the filter cutoff or the pitch. The envelope gives the note its shape, while the oscillator gives it its tone.

The four stages run in order when a key is pressed. The attack rises from silence to peak. The decay falls from the peak to the sustain level. The sustain holds that level while the key stays down. The release falls from the current level to silence after the key is lifted.

Sustain is the only stage defined by a level rather than a time. It is a percentage of the peak. A sustain of 100 percent keeps the sound at full level, and a sustain of zero makes the envelope behave like a pure attack and decay shape, with the sound dying away even if the key is still held.

Attack: how the sound arrives

Attack sets the time it takes for the envelope to reach its peak after a key press. Short attacks create percussive sounds with a clear onset, such as plucks, keys and drums. Long attacks create sounds that seem to grow out of nothing, such as pads and strings.

Very short attacks, under a few milliseconds, produce a sharp click at the start of the note. That can be useful for percussion or for emphasizing rhythm, but it may sound harsh on sustained tones. Attacks of around 10 to 50 milliseconds soften the start without making the note feel late.

Long attacks can delay the perceived timing of a note. If a pad with a two-second attack is played in time with drums, the chord will seem to arrive after the beat. This is intentional in some styles and a mistake in others, so check the timing against the rhythm.

Decay: the fall to sustain

Decay sets the time to move from the peak level down to the sustain level. Short decays give a quick drop that suits plucks and stabs. Longer decays create a gradual settling, which is useful for piano-like tones and for bass sounds that need a strong start and a calmer body.

When the sustain level is at 100 percent, the decay has no visible effect, because the envelope never falls. That is a common reason a patch seems to ignore the decay control. Lower the sustain first, then adjust the decay to hear its effect.

Sustain: the level you hold

Sustain sets the level the sound holds while the key remains pressed. It is often the most important control for the character of a patch. High sustain keeps the note loud and full, which suits organs, strings and synth leads. Low sustain makes the note fade even while held, which suits plucks, bells and many percussive tones.

A useful way to think about sustain is that it sets how much of the sound's energy remains after the initial attack. A sustain of 50 percent means the note is half as loud as its peak during the held portion. Because perceived loudness follows decibels rather than linear amplitude, a 50 percent sustain (about minus 6 dB) sounds roughly two-thirds as loud as the peak, not half, but the direction of the change is still clear.

Release: the tail after the key

Release sets the time it takes for the sound to fade to silence after the key is lifted. Short releases stop the sound quickly and keep rhythmic parts tight. Long releases let notes ring out and overlap, which creates pads, atmospheres and sustained reverb-like tails.

Release is also a common source of mud. A long release on a bass line can blur one note into the next, and a long release on a lead can fill the mix with leftover sound. Match release length to tempo. A release shorter than the gap between notes keeps the rhythm clean, while a longer release can be used for effect.

Curve shape changes the feel

Most synthesizers do not move the envelope in a straight line. Many use exponential curves for decay and release, because exponential movement sounds more natural to the ear. Linear curves can sound abrupt, especially at the end of a decay. Some synths offer a choice, and switching between them can change a patch noticeably.

Attack curves also matter. A linear attack reaches the peak evenly, while a curved attack can start slowly and rise quickly, or start quickly and then slow down near the top. Trying both curves on the same patch is a fast way to learn how much the shape matters.

Starting settings for common sounds

The table below gives starting points, not fixed rules. Adjust each value while listening to the sound in context, and always remember that the tempo, the key and the other instruments affect how a patch feels.

Sound	Attack	Decay	Sustain	Release
Pluck or pizzicato	1 ms	200 to 500 ms	0 to 20 percent	100 to 300 ms
Synth bass	2 to 5 ms	150 to 400 ms	40 to 70 percent	50 to 150 ms
Organ	5 ms	Not important	100 percent	30 to 80 ms
Warm pad	800 to 2000 ms	500 to 1500 ms	70 to 90 percent	1000 to 3000 ms
Brass stab	20 to 60 ms	200 to 400 ms	60 to 80 percent	100 to 250 ms

Use these values as a map, not a recipe. A pluck with a sustain of zero will sound very different from a pad with the same release, and each setting interacts with the filter and the oscillator.

Using envelopes beyond loudness

The same ADSR shape can control the filter cutoff, the pitch or the level of an effect. A filter envelope with a short decay gives a bright attack that closes quickly, which is the classic synth bass sound. A pitch envelope with a very short decay can add a small upward or downward sweep at the start of a kick or a tom, giving it an impact that a static tone lacks.

When you connect an envelope to a parameter other than loudness, start with a small amount. Large values can make the sound unstable or cause unwanted sweeps. Listen to the patch with the envelope amount at several settings and choose the one that adds character without drawing attention to itself.

Common mistakes

The most common mistake is trying to fix a patch with the envelope when the oscillator or filter is the real problem. If the sound is too thin, a longer envelope will not add harmonics. Check the source first.

Another mistake is ignoring the release on repeated notes. A patch that sounds clean on a single note can smear badly in a sequence. Play the patch with the rhythm of the track before you finish it.

Finally, avoid using very long attacks on sounds that need rhythmic precision. A slow attack is excellent for pads but can make a lead or bass feel late. Choose the envelope that serves the musical role of the sound.

Key takeaways

An ADSR envelope describes how a note changes over time. Attack sets the onset, decay sets the fall, sustain sets the held level and release sets the tail.

Sustain is a level, not a time, and it often has the largest effect on the character of a patch. Start there when a sound feels wrong.

Use the envelope to shape the sound in context. Match attack and release to the tempo, and listen to the patch with the rest of the track before deciding it is finished.