Simple Synth

Envelope describes how a sound changes over time.

• Attack: Time taken for initial run-up of level from nil to peak, beginning when the key is pressed.
• Decay: Time taken for the subsequent run down from the attack level to the designated sustain level.
• Sustain: Level during the main sequence of the sound's duration, until the key is released.
• Release: Time taken for the level to decay from the sustain level to zero after the key is released.