So these are the most common parameters that you will find on the envelopes of almost any synthesizer.
Nevertheless, there are some synths that include other controls. These aren’t that common, but it’s important to know that they exist.
First, we have the hold control. This parameter is between the attack and the decay, and controls how much time the sound will stay at its maximum value before decaying, and it will keep playing even if we release the note.
This is mostly found in older synthesizers such as the Korg MS-20, but some modern VST plugin software such as Serum also include it. The envelopes that include this hold option are called AHDSR
Also, although this is even less common, some synths have a delay parameter. This one goes before the attack, and determines the length of silence between pressing a note and the attack.
The envelopes that include this delay option (such as the Prophet ’08) are called DADSR. Some synths even go further and include both hold and delay controls and have a DAHDSR envelope (such as Image Line’s 3xOsc included in FL Studio, which is surprising due to its general simplicity)