The Full Form of VCA is‍ Voltage Controlled Amplifier.

A VCA is a processor that can alter the amplitude of a signal proportional to the control voltage applied to its amplitude modulation control input. In simple words it is just an amplifier whose output you can control with a control signal.

A voltage-controlled amplifier (VCA) has two kinds of inputs:

• Carrier (Signal Input)

This is the input where a bipolar signal comes in. Subsequently, it is the main signal and all the alterations are made to this signal.

• Modulator (Control Input)

Usually a Uni-polar positive signal comes in through this input, which makes alteration to the bipolar signal coming from the signal input.

A VCA is an amplifier, which usually accepts bipolar signal at its carrier or signal input and a uni-polar positive signal at its modulator or control input. Furthermore, the output signal is the instantaneous product of both of these signals. It is the multiplication of both the amplitudes at each instant in time.

A lot of VCA’s have gain knobs, available for setting to different values. A carrier signal can only pass through a VCA if either a positive bias is provided or a positive signal comes in through the control input. So when it is biased to 0 and no modulator signal comes in then no signal will be present at the output. It is for this reason usually a uni-polar positive signal is provided to the control input. In addition, if the sound needs to collapse frequently for certain effects, a bipolar signal is also sent.