The rubber hits the road on this module with the Instant / Gate / Zero Crossing Detector switch and CV input. Normal operation happens in the Inst mode where the VCA will follow the CV signal as it is seen.
Things get more interesting when you enter Gate mode which causes the CV to be updated ONLY on a rising edge of the signal going into the Update G/ZCD jack. This jack has the In jack's signal normaled to it. Gate mode allows the Digital VCA to sample and hold a control voltage, very useful for pulling modulation data out of other sources. This mode uses a Schmitt trigger to ensure noisy signals can be used without causing multiple unintended updates.
The Zero Crossing Detector is the crown jewel of the Digital VCA. This little circuit only allows the VCA to be updated when the Input signal (or Update G/ZCD signal) is at 0 Volts. This eliminates popping and clicking normally associated with fast envelopes. It allows you to use a Gate signal directly as an envelope without annoying pops!
WMD would like to thank Suit & Tie Guy (STG Soundlabs) for the concept. STG Soundlabs will be releasing a 5U/MU format version of the Digital VCA.