What is ADSR?

ADSR refers to the four stages of an envelope, which are Attack, Decay, Sustain, and Release.

Attack describes the amount of time the envelope takes to reach the maximum volume. This could be instant or a gradually rising sound.

Decay relates to the amount of time the sound takes to drop from the maximum volume down to the sustain stage.

Sustain is the level of volume that the note is held at, it is not a measure of time and could, therefore, be maintained indefinitely.

Release describes the amount of time it takes for the sound to drop back to zero after key release or the sustain has ended.