Envelope is widely used in synthesizers, not only generate sound, it can also modulate almost everything in synthesizers, an example is LFO.
Here we are only going to talk about the basic of synth envelope.
What is Synth Envelope?
Just like sound envelope, synth envelope can also be divided into 4 sections, Attack, Decay, Sustain and Release. When you press the key on a keyboard or trigger a signal, it will generate a wave that goes through each stage.
The time of a wave going from zero (key pressed or triggered) to its maximum amplitude.
The time of a wave drop from its maximum amplitude to sustain level.
The level of a wave when its amplitude is stabilized. The sustain time depends on how long you hold the key, sustain stage can last forever if the key is being held. Note that the parameter of sustain is level, not time.
The time of a wave drops from sustain level to zero after the key is released.
Not all envelopes look like the envelope we just talked about, besides ADSR, some synths will have more controls.
Sustain time can be a positive or negative value when the time is a positive value, it’s called “Rise time”, and when the time is a negative value, it’s called “Fall time”.
The time of a wave rises from sustain level back to its maximum level.
The time of a wave falls from sustain level to zero. If the key is released before the level fall to zero, then it will go to the release stage, so the setting of release time will still have an effect.
The time of a wave stabilized at its maximum amplitude before decay. Some synths will show AHDSR, instead of ADSR, the “H” is the hold time.