Topic summary
sustain
Extracted from the Wikipedia article Envelope (music).
Other envelopes
Some systems use only attack or release stages, or add additional stages. The Korg MS-20 adds a "hold" stage, which can be used to sustain a note after releasing a key, similarly to a sustain pedal. It also adds a "delay" stage, which allows the user to set a time before the envelope initiates. Yamaha created an envelope that removes the sustain stage and adds "initial" and "after" steps for the attack.