This is the classic Moog filter that changed the sound of electronic music.

Reach out and sweep the filter with the CUTOFF knob. Or use the ENVELOPE section to do it automatically. Or plug in one or more expression pedals or control voltages to do it. Or do all three. This is the best-sounding, most playable filter you can have!

What is a Moogerfooger MF-101 Lowpass Filter?

A lowpass filter removes high frequencies from a tone. It makes the tone sound much more mellow or muted. The lower the cutoff, the more muted the tone sounds. Imagine a window shade. As it is pulled down, it cuts out the higher light, then the light from the middle of the window, then finally all the light. A lowpass filter does the same sort of thing to the sound spectrum.

The moogerfooger filter is a direct descendant of the original Moog modular synthesizers. It contains two complete modular functions: a voltage-controlled lowpass filter and an envelope follower.

The envelope follower tracks the loudness contour (envelope) of a sound, and produces a voltage that follows the dynamics of your playing. Every time you play a note, the envelope voltage goes up and then down. The harder you play, the higher the envelope voltage goes. The envelope follower opens and closes the lowpass filter. Think of the envelope voltage as an invisible hand that turns the CUTOFF knob up and down every time you play a note. Since the envelope follows the dynamics of your instrument’s signal, you actually play the filter as you play your instrument.

The moogerfooger filter is also a resonant filter. As you turn up the resonance, the overtones near the cutoff frequency are boosted. Resonance gives the moogerfooger filter the same classic Moog filter sound as the Minimoog^“! and Moog modular synthesizers.

The moogerfooger filter 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. 1/4″ jacks are provided for audio input and output, pedal/control inputs and envelope follower output.

Moog MF-101 main features include:

• CUTOFF rotary control, which varies the filter’s cutoff frequency over an eight-octave range.
• RESONANCE rotary control, which varies the shape of the filter’s response, from pure lowpass to actual oscillation.
• ENVELOPE AMOUNT rotary control, which adjusts the amount that the input signal’s envelope sweeps the filter cutoff frequency.
• MIX rotary control, which crossfades continuously from unfiltered to filtered audio.
• DRIVE rotary control, which adjusts the gain of the audio input.
• SMOOTH-FAST rocker switch, which chooses between smooth and fast envelope follower response.
• 2-POLE 4-POLE rocker switch, which chooses between 2-pole (bright) and 4-pole (deep) filter frequency response.
• LEVEL, a three-color LED that is used to set the DRIVE control.
• ENV, a LED that indicates the strength of the envelope voltage.
• BYPASS, a two-color LED that tells whether the filter is on or bypassed.
• ON/BYPASS, a rugged, smooth-acting stomp switch.
• AUDIO IN 1/4″ phone jack – accepts any instrument-level or line-level audio signal from -16 dBm to +4 dbm.
• AUDIO OUT 1/4″ phone jack – -4 dBm nominal output level.
• CUTOFF, RESONANCE, AMOUNT, MIX, all of which are stereo 1/4″ jacks that accept moogerfooger EP1 (or equivalent) expression pedals, or control voltages from either two-circuit or three-circuit 1/4″ jacks.
• ENVELOPE OUT jack – delivers the Envelope Control voltage for use by other voltage-controlled devices.
• +9V POWER INPUT jack
• CASE: Black panel with hardwood sides – classic analog appearance.
• DIMENSIONS: 9″ x 6″ x 2-1/2″
• NET WEIGHT: 2 lb