The EMG VMC is and active variable mid control EQ Circuit for bass and guitar. Rotate the upper control of the stacked pot clockwise for boost, counterclockwise for cut. Leave it in the center detent position for a flat response. Rotate the frequency knob on the bottom to sweep through the mid-frequency band (from 100 Hz to 1000 Hz) for even more tonal options. The VMC can be used in combination with the EMG BT (Bass/Treble) controls as well as any of the other EMG accessories.