ADSR

ADSR stands for Attack, Decay, Sustain, and Release. It is a type of envelope generator used in many electronic synthesizers and samplers to shape how a sound's level evolves over time. By controlling amplitude (or other parameters) with an ADSR, musicians can create a wide range of sounds, from sharp plucks to smooth pads.

Attack is the time it takes for the level to rise from zero to its peak after a note begins. Decay is the time for the level to fall from the peak to the sustain level. Sustain is the level kept while the note is held. Release is the time for the level to fall to zero after the note is released. Values are usually expressed in milliseconds or seconds, and the curves can be linear or exponential, affecting how quickly each stage progresses.

In synthesis, the ADSR commonly controls the amplitude via a voltage-controlled amplifier, but the same envelope can modulate other parameters such as a filter cutoff, vibrato depth, or modulation depth. The sustain level is a steady state level during the note’s on time, while the attack and release phases determine how quickly the sound enters and exits that state. Short attack and release times yield percussive sounds; longer times produce smoother, faded endings.

Implementation notes: the envelope is typically triggered by a gate or note-on signal and terminated by a note-off signal. Some instruments offer alternative curves or additional stages (for example, variations like DADSR or multi-stage envelopes), but ADSR remains a foundational model in many devices.