attackdecaysustainrelease

Attack-decay-sustain-release (ADSR) envelope is a fundamental concept in subtractive synthesis and digital audio production. It describes the time-based shaping of a sound’s amplitude, and sometimes other parameters, in response to a note being played and released. The envelope has four stages: attack, decay, sustain, and release.

Attack is the time it takes for the sound to reach its maximum level after a key press. A short attack yields an immediate onset, while a longer attack produces a gradual swell. Decay follows the attack and defines how long the level drops from the peak to the sustain level. Short decay creates a quick transition; longer decay smooths the drop. Sustain is a level rather than a time parameter and determines the amplitude held while the key remains pressed. The sustain level sets the ongoing height of the sound during the note’s duration. Release is the time it takes for the sound to fade from the sustain level to silence after the key is released. A longer release yields a lingering tail, while a shorter release cuts off more abruptly.

ADSR envelopes are commonly used to control amplitude, but they can modulate other parameters such as filter cutoff or pitch, shaping the instrument’s timbre over time. They are essential for creating a wide range of sounds—from percussive, quick-onset notes with short releases to lush pads with long attack and release. Some synthesizers include variations or additional stages (e.g., AR, ASR, or expanded envelopes) to alter the envelope’s behavior.