ADSR stands for attack, decay, sustain, and release and is used to model the timbre of an instrument. The timbre or tone quality is determined by various factors such as the way the sound is produced and the material of the instrument. Different families of instruments have their own characteristic ADSR profiles. The attack refers to the phase in which the sound is initiated. This could be the fast attack of a strum on a guitar or the slower one of a pipe organ. The decay phase occurs immediately after the attack impulse and describes how rapidly the sound dies. Some instruments like a drum have extremely fast decay and the sound is virtually nonexistent after the attack. The sustain profile of an instrument refers to how long the sound resonates for when it is played. String instruments such as a violin have an extremely long sustain because the violin’s sound box is receiving constant vibrational energy from the bowed string. Finally, the release phase describes how rapidly the sound fades away once the instrument is not being played.
