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 also be triggered by slow rising CVs too due to the built in schmitt trigger function. No additional 'trig' input is required.

The ADSR/VCA allows for blisteringly fast minimum attack and decay times. And yet, the controls with their true exponential response allow you to adjust the times with ease.

Also on this module is an LED. This gives a visual indication of the output level of the internal ADSR waveform.