The envelope follower opens and closes the lowpass filter. The moogerfooger filter is also a resonant filter. As you turn up the resonance, the overtones near the cutoff frequency are boosted. The moogerfooger filter's control parameters are signal mix, cutoff frequency, resonance amount, and envelope amount. All of the Lowpass Filter's parameters can be controlled with expression pedals or external control voltages as well as by rotary panel controls.
Panel switches select filter mode and envelope follower speed.
MIX rotary control, which crossfades continuously from unfiltered to filtered audio. ENV , a LED that indicates the strength of the envelope voltage.