ADSR (Attack, Decay, Sustain, Release) is a term used to describe the shape of sounds over time (see also envelope).
- Sounds that begin very quickly (for example a click) can be described as having a fast attack. Sounds that begin more gradually can be described as having a slow attack (for example: the sound of an apporaching car). Removing the attack of a sound can significantly affect what we hear (bell example).
- The Decay of a sound is the time which it takes for the attack portion of the sound to reach a steady Sustain.
- The sustain of a sound is how long it continues to vibrate and sound. A click has very little sustain, while a bell often has a long sustain. The sustain portion of a sound can be isolated and looped to extend sounds or to create new and steady sounds.
- The release of the sound is the way in which the sound finally ends.
Affecting the envelope of a sound can greatly change the characteristic of a sound. When sounds are reversed their envelope is also reversed, and it is often this that leads to the greatest difference in sound quality (sound example).
When creating new sounds on a synthesiser it is often possible to control the shape of ASDR envelope, and when composing with recorded sounds it is often very useful to imagine the ADSR envelope shapes. Combining sounds with similar envelope shapes can help to link the sounds together (sound example), while contrasting sounds that have very diffrerent ADSR envelopes can create rich textures.