- Input Level
- controls input volume. The Input Level control goes straight into all four filter tubes.
- Filter CV Sweep
- if nothing is plugged into the Filter CV In jack, this control can be used to sweep all 4 filters simultaneously. The usual effective range is from about 9 o'clock to 3 o'clock on this knob.
- Tune (4x)
- each filter is independent of the others, except for their signal inputs, signal outputs, and the Filter CV Sweep. Each filter may be tuned to a different point on the one-octave range of the filter, using its own TUNE knob. The panel around the Tune knobs is marked to indicate the approximate location of each equal-tempered major division within that 1-octave range. The range is from F2 to F3. The Tune controls set the lowest sweep point for that filter; the Filter CV Sweep still affects all the filters in parallel (they can still sweep from that setting up to the maximum, approximately the F3 note).
- Resonance (4x)
- each filter may also have its "ringing" or resonance effect set independently. This is the "sharpness" or "peakiness" of the bandpass peak. By turning Resonance for a filter fully counterclockwise, that filter is effectively removed from the circuit. At approximately the 10 o'clock point on the Resonance knob, that filter will start to oscillate, or generate its own tone. This first becomes apparent at the midpoint settings of the Tune or Filter CV Sweep controls. Turning Resonance fully clockwise forces that filter to oscillate strongly--this allows its use as a signal source, or allows it to cross-modulate with any input signal.
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