So this is a right weirdo! Coming from a want for a smaller filter for some voices, this, an oscillator and an envelope generator can be put together to be a small synth voice with distortion and uniquely strange characteristics.

The filter has different behavior depending on where the oscillator is in the offset. It’s well suited for unipolar waveforms (all in + territory as in the #1222 Performance VCO) but still works great with bipolar ones.

Starting from the LM13700 data sheet lowpass filter, the circuit has been pushed, tweaked and expanded to produce some very funky sounds indeed. It’s full of character and you can even get it to step and stuff. It’s proper odd.

Its a funky filter that sounds completely different depending on wether you put unipolar or bipolar waveforms into it (you can bounce between with the Shelf switch to increase its characteristics)