Moog Music MF-101 Lowpass Filter - Manual (Page 5)

Your MF-101 also contains a classic envelope follower. An 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 signal follows the amplitude (loudness) of the sound which it represents.
The envelope follower output 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.
TOURING THE PANEL FEATURES
The Filter Section
Let's look at the Filter section first. The two control knobs are CUTOFF and RESONANCE.
The 2-POLE 4-POLE switch selects the filter’s operating mode. All three of these affect
the sound of the filter.
The CUTOFF knob opens and closes the filter. As we said above, the filter lets through
the low overtones and cuts off the higher overtones. As the filter closes, more and more
of the high overtones are cut off. The CUTOFF knob is calibrated in Hz. (vibrations per
second). The cutoff frequency is about 15 Hz when the knob is counterclockwise, 500
Hz (about an octave above middle C) when the knob is in mid-position, and 12 kHz,
(12,000 vibrations per second) when the knob is clockwise.