This module is based on the Aries 312 ADSR, which was originally sold as a kit in 1975 ($49.50). It is a nice early design that does not use CMOS (logic chips) or a micro-processor; instead it is discrete – meaning all transistors, diodes and passive components (capacitors & resistors). This was common in the 60s but became rarer and rarer as op-amps became cheaper.

ADSR stands for attack, decay, sustain and release, check wikipedia for a full description. An extra feature of this module is the separate trigger and gate inputs. The envelope will remain in the ADS stages whilst the gate is high and enter release when the gate stops. The trigger input allows you to retrigger the envelope whilst in the ADS stages. This allows you to set up complex envelopes which can be very interesting and allow your sounds to move away from the standard musical paradigms.