Everything in here is voltage going somewhere

A gate arrives. A voltage starts moving. That movement is the envelope, and almost everything else — the timbre, the dynamics, the sense of physical attack — follows from how that voltage travels through four distinct phases. People talk about envelopes as if they were shapes drawn on a screen, but a hardware envelope generator is not drawing anything. It is charging and discharging capacitors through variable resistances, and the shape you see on an oscilloscope is the electrical consequence of those physical events, not a target the circuit is trying to match.