It's a voltage controlled envelope filter with 3 modes: Up Sweep, Down Sweep and Sample and Hold. The Range knob, in combination with pick attack, controls the sensitivity and reaction time of the envelope and thus the width of the frequency sweep. The higher the Range and harder the attack equals a faster reaction time and higher frequency sweep and vice versa. In the Sample and Hold mode the filter is controlled by random voltage and the Range controls the speed. The filter can be cross faded between high pass (counter clockwise), band pass (center) and low pass (clockwise) for a wide variety of voices. The Resonance control goes from zero to the brink of oscillation and adds more body and ring to the filter voice. The new v2 version features EarthQuaker Devices’ new Flexi-switch which allows for latch or momentary operation.