So, "What's a Voltage Controlled Amplifier?" I hear you say, it's a specially designed type of amplifier in which the gain, or amplification it produces is controlled by a DC voltage applied to it's C.V. (Control Voltage) input, the higher the voltage, the higher the amplification, a Voltage Controlled Amplifier, or VCA, is typically used to control the dynamics, or loudness, of a signal in a Modular Analog Synthesizer, and to give the signal Attack, Decay, Sustain, and Release characteristics.