The Amount knob determines how much the envelope varies the filter. When the knob is counterclockwise, the envelope signal has no effect on the filter. When the knob is fully clockwise, the envelope signal opens and closes the filter over a range of five octaves.
The Smooth/Fast switch determines how closely the envelope tracks the loudness of the input signal. Some sounds (like guitar chords) have long, rough envelopes, and often sound better with less dramatic changes in the filter. Other sounds (like bass or snare drum) are quick and sharp, and sound great when the filter closely tracks their attack.
The Mix control blends the original input signal with the filtered signal. Use it to get any mixture of filtered and unfiltered sound.
Cutoff opens and closes the filter. Turned counterclockwise, fewer high frequencies pass through the filter. Turned clockwise, more high frequencies pass.
Resonance changes the way the filter sounds. At low resonance, low frequencies come through evenly. At high resonance, frequencies near the cutoff frequency are boosted, creating a whistling or vowel-type quality. When resonance is maxed out, the filter oscillates and produces its own tone at the cutoff frequency. This oscillation interacts with other tones as they go through the filter, producing the signature Moog sound.
The 2-Pole/4-Pole switch selects whether the signal goes through half the filter (2-pole) or the entire filter (4-pole). 2‑pole is brighter, while 4-pole has a deeper, mellow quality.
The Drive control sets the input gain. Use it to adjust the input to the filter and envelope follower for desired impact.
Bypass glows either red (bypassed) or green (not bypassed) to show whether or not the effect is in the signal path.