An “ASR” envelope stands for Attack, Sustain, and Release, which are three stages of an envelope generator used to shape the amplitude or other parameters of a sound over time. The ASR envelope is a simpler version of the more common ADSR (Attack, Decay, Sustain, Release) envelope, with the Decay stage removed. The three stages of the ASR envelope are:
- Attack: This is the first stage, during which the control voltage rises from its initial value (usually zero) to its peak value. The attack time determines how quickly this rise occurs, with shorter attack times producing a faster, more immediate onset of the sound, and longer attack times creating a slower, more gradual increase in amplitude or other parameter.
- Sustain: This is the second stage, during which the control voltage remains at its peak value for as long as the note is held or the gate signal is active. Unlike the other stages, the sustain stage does not have a specified duration; instead, it is determined by the length of the gate signal or the amount of time the note is held.
- Release: This is the third stage, during which the control voltage falls from its peak value back to its initial value after a note is released or the gate signal is deactivated. The release time determines how quickly this decrease occurs, with shorter release times producing a faster, more abrupt fade-out of the sound, and longer release times resulting in a slower, more gradual decay.
By adjusting the attack, sustain, and release parameters, a musician can shape the dynamic characteristics and articulation of a sound, offering a range of expressive possibilities. ASR envelopes are suitable for various types of sounds, including pads, leads, and plucked or struck instruments, where the sustain portion of the sound is determined by the length of the gate signal or the duration of the held note.
