From the Oakley website:
This is a dual purpose module in a 2U width panel. Not only does it feature the classic four stage envelope generator with full voltage control, but it also has a high quality VCA onboard.
This highly useful circuit implementation hardwires the ADSR generator to the control input of the VCA. The signal at the VCA’s other input, the IN socket, will then be multiplied by the ADSR waveform. You can use any signal into this input, audio or CV. If you use CV, then the ADSR output level will be governed by the level of the CV. If you use audio, then the ADSR waveform will control the volume of that audio signal.
A typical use would have the IN socket being driven by the velocity CV from a midi-CV convertor. Thus the harder you hit the keys, the greater the ADSR output level. If you use this to control a filter sweep, this can create brilliantly effective touch sensitivity to your patch.
The circuit is configured so that if nothing is plugged into the IN socket, the module will behave as a traditional ADSR module. The output will rise to +5V at the attack peak.
The ADSR is operated by a gate signal, but can be triggered by slow rising CVs too, due to the built in schmitt trigger function. No additional ‘trig’ input is required.
This design features blisteringly fast minimum attack and decay times. And yet, the controls with their true exponential response allow you to adjust the times with ease.
Each CV input is controlled by a dedicated pot. This pot acts as a reversible attenuator, so that the gain of the input is anything from -1 to +1. This means that any inputted CVs can subtract or add to the times, or level, set by the ADSR pots. With any input knob set to its middle position, then that CV channel is effectively turned off.
Also on the module is an LED. This gives a visual indication of the output level of the internal ADSR waveform.
Input CV normalling, so that with one CV into the Attack CV input this CV is also connected to the Decay and Release CV inputs when those have nothing plugged into them. Release CV is normalled from the Decay CV, as part of this scheme.