The analog module based on a resistive optocoupler is designed to simulate the characteristics of natural instruments (violins, wind instruments, guitars, etc.). It is known that natural instruments tend to change the harmonic composition depending on loudness. The notes which are pressed more loudly have more harmonics, overtones.
LPG, which includes a controllable low-pass filter and voltage controlled amplifier, allows you to obtain a different cut of high frequencies, depending on the volume of notes.
It is also possible to work in VCA and filter mode.
In the filter mode the module gets access to the resonance and cut-off frequency control. The external CV has a sensitivity adjustment and a polarity switch - it aims to control the frequency of the filter. The scheme makes it possible to obtain a self-generation effect at high resonance values.
The controlled amplifier mode (VCA) allows you to get a processed non-distorted signal. CV is aimed at controlling the gain of the circuit.
The "ping in" input allows to get a short VCA pulse from the gate signals.