ADSR Envelope

What it means

The ADSR envelope is a control curve used in electronic sound synthesis that defines how a sound parameter—usually volume—changes over time. Its name comes from the four phases it moves through: Attack, Decay, Sustain, and Release.

During the attack phase, the value rises from zero to a peak as soon as a key is pressed. During decay, it falls from that peak to a middle sustain level. Sustain itself is not a duration but a level: as long as the key is held, the sound stays at that height. Only when the key is released does the release phase begin, during which the value fades back down to zero.

In the notation

The ADSR envelope has no place in conventional music notation. Synthesizers and music software display it as a graphic curve or as four knobs controlling the attack, decay, and release times along with the sustain level.

Musical use

An ADSR envelope can imitate the behavior of many acoustic instruments or shape entirely new sounds. A fast attack with a short decay and low sustain produces percussive sounds, like a piano or drum, where the tone dies away quickly after being struck. A slow attack with a high sustain instead produces soft, swelling pad sounds typical of strings or synth pads.

The envelope often shapes not only volume but other parameters too, such as filter cutoff or pitch, adding further movement to a sound. Modern synthesizer software often offers extended envelopes with additional stages, but the four-phase ADSR model remains the most common basis for shaping a sound.

Performance practice

When programming your own sounds, it helps to think of the four phases as modeling a real instrument: how quickly the tone begins, how quickly it fades after being struck, how loud it stays while held, and how long it lingers after release. Adjust each control on its own and listen closely to the instrument character that emerges.