What is an envelope curve


Envelope, ADSR model

The overall volume curve of a tone is called the envelope and can be represented graphically similar to a vibration image. The course of time is shown on the horizontal axis, the volume (amplitude) on the vertical axis.

The so-called ADSR model has proven itself for a schematic, simplified representation of the envelope curve. It divides the volume curve into 4 phases:

- Attack is the phase from the triggering of the event (e.g. by pressing a key) until the maximum volume is reached.

- Decay is the phase in which the sound drops from the volume maximum to the volume of the sustain phase.

- Sustain is the phase in which the sound maintains a constant volume. The length depends, for example, on how long the key is held. Therefore the sustain value is not a time value, but a volume value.

- Release is the phase in which the volume drops from releasing the key to zero.

This model is often used for sound synthesis on programmable synthesizers. All 4 phases can be regulated separately. The ADSR model is also used for other components of sound programming, e.g. filter setting and even pitch.