ADSR Envelopes Explained: 4 Stages of an ADSR Envelope

An envelope is a term used to describe the evolution of a sound in a piece of music. Envelopes are fed through an envelope generator, the component within an analog synthesizer (synth) or plugin in computer software that signals when and how a sound should change. The envelope defines the trajectory and modulation of a sound, while the envelope generator controls the behavior of the envelope.

An ADSR envelope is a type of envelope control mechanism commonly found in the synths and samplers used in electronic music. ADSR stands for the envelope's four stages of modulation: attack, decay, sustain, and release. These stages control the level of the sound from the moment you press a key or advance a music sequencer.

In music production and sound design, ADSR envelopes are typically used to control the loudness of a sound. ADSR envelopes typically produce a sound that takes the shape of a waveform—rising in the attack stage, slightly declining during the decay stage, plateauing during the sustain stage, and finally falling at the return stage.

An ADSR envelope features these four stages.

1. 1. Attack: The attack phase begins the moment a key is pressed. This phase determines how quickly a sound reaches full volume before entering the decay phase. On an analog synth, this phase is typically instantaneous. Some modern synthesizers—like MIDI pad controllers—allow for the attack time to be delayed.
2. 2. Decay: The decay phase determines the length of the drop from the peak level to the sustain level of a sound. The decay time can often be altered to change the overall sound. For instance, a short attack and a long decay will produce a sound that reaches maximum amplitude quickly and falls slowly to the sustain level.
3. 3. Sustain: The sustain phase does not specify a length of time. Instead, it determines the volume of a sound for the entire hold time between the decay and release phases.
4. 4. Release: The final phase determines the speed at which a sound ends from the moment you release the key. Depending on the desired sound, the release time can be short or long.

Using an ADSR envelope generator, you can alter the stages of the envelope to make even more complex sounds.

1. 1. Long attack, long release: By lengthening the attack and release times, you can create rich, lush tones.
2. 2. Short attack, short release: By shortening the time of the attack and release phases, you can create percussive, staccato sounds.
3. 3. Long release time: Give your sounds a tail by lengthening the time of the release phase. This comes in handy when building sounds to mimic percussive instruments like snares or hi-hats.
4. 4. Short sustain, long decay: Highlight the peak levels of a waveform by shortening the sustain and drawing out the decay.

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