The idea of a voltage-controlled amplifier (VCA) is that an audio or control signal is patched to its input, and externally controlled voltage controlled via the Control Inputs jacks. This is useful for turning audio or control signals on or off, applying envelope volume curves to sounds, regulating the amount of modulation signals applied to audio signals, and more. The VM902 VCA very closely replicates the unique tone and overdrive characteristics of the original 902 VCA design.