Dual filter, for metal heads

The Spectral Devastator features a brand new filter core, designed by FSS through finding ways to implement voltage control for a resonant active filter. The method of CV involves passing the audio input through the CV stage, but whilst the CV implementation is non-linear, distortion and waveshaping of the audio occurs, particularly with high resonance. This circuitry also results in a filter that self oscillates not sinusoidally, but with a sawtooth-like waveform.

http://www.futuresoundsystems.co.uk/fil2.htm