The Keyboard - Arturia KORG MS-20 V User Manual

MS-20 EG1: Delay, Attack, Release
EG1 has three stages: Delay, Attack, and Release. The Delay time is just what it sounds like:
a time delay between pressing a key and the start of the Attack.
MS-20 EG2: Attack, Decay, Sustain, Hold, Release
EG2 has five stages: Hold, Attack, Decay, Sustain, and Release. The Hold time is an added
time that the envelope stays at the Sustain level between when the key is released and
when the Release stage begins.

8.2.2. The keyboard

The usual way we start and stop a note is to play the keyboard. On an analog synthesizer,
the keyboard sends at least two signals: a control voltage to set the frequency of the VCOs
(so they play the right pitch), and a gate signal that opens when the key is pressed and
closes when it's released. When we play a note, the attack and decay happen, followed by
the sustain. When we let go of the key, then the release happens. These signals shape the
volume of a note (starting and stopping it) and its tone over time (to simulate the behavior
of acoustic instruments, etc). Naturally, on KORG MS-20 V, these signals come from a MIDI
controller.
121 Arturia - User Manual KORG MS-20 V - The Basics of Subtractive Synthesis