Two kind of filters selectable through dedicated toggle button.
Self-Oscillation possible with 24dB filter, when you see the LED start to become brighter (up S.O. label) as long you turn RES knob clockwise, you can use such switch to mute the input signal and use the Sine waveform from the filter.
KBD TRACK (Keyboard Tracking) allows the value of the note played on the keyboard to also affect the Cutoff frequency of the Filter : In the 1:1 position, the value of the note played on the keyboard will affect the Cutoff frequency at full value. ; In the 1:2 position, the value of the note played on the keyboard will affect the Cutoff frequency at half of its full value ; In the OFF position, the keyboard Tracking is off, and the value of the note played on the keyboard will have no effect on the Cutoff frequency.
You can use the filter itself like a Sine wave oscillator patching the output to the input, rising the Resonance to max and then turning on the S.O. switch, KBD Track to vary the pitch and cutoff for frequency.