Side chain compression :

The audio signal (for example the total final mix) is supplied to the INPUT of the VC-SC, the OUTPUT of the VC-SC is connected to the DAW, Recorder or PA mixer. To the VC-SC Side-chain RETURN you connect a signal that must compress the total mix (for example a KICK drum to pump the final mix or maximize the average signal level without overload by the KICK drum). Place the Cutoff LP/HP switch in "Ext S-Chain" position. Then set the desired compression level using the pots such as RATIO, THRESHHOLD, CUTOFF etc.