The Four Play by Behringer is a quad VCA with mixer function. Each of the VCAs can be crossfaded between linear and exponential characteristic, has its own level control, a level LED and of course signal and CV inputs and an output. In addition, each channel has a boost switch that boosts the signal by 6dB. Since the CV inputs and signal outputs are normalized, combinations are also possible: If audio signals are present at channels 2-4 and an envelope is applied to channel 2, the sum processed by the envelope is present at output 4. This leaves channel 1 free to control the intensity of an LFO with Velocity .