This is a looping, retriggerable ADSR envelope generator. The main circuit design is from the Kassutronics blog. Unlike many envelope generator designs, it uses op amps with diodes as “precision rectifiers” to prevent the problem where the release slows down drastically below 700 mV, taking tens of seconds to get to near 0 V. A push button allows manual gating. There is an inverted output and an indicator LED. For my version I added two features: A retriggering input, allowing multiple Attack-Decay cycles during the Sustain phase, and a looping mode in which Attack-Decay envelopes repeat themselves automatically as long as a gate is applied (gated looping) or continuously (ungated looping). Additionally there are switch selectable time ranges and the option of socketing the timing capacitors.