Six parallel filters (lowest LP, highest HP, the rest is BP). Left two knobs control the levels of individual filter outputs (central spot of the mix and spread/focus). Right two knobs control the resonance of individual filter outputs (central spot and spread/focus).
"Spread" knob moves filters frequencies closer/apart. Big knob sets frequency of the first/lowest filter (other frequencies are calculated based on this and "spread" parameter). There is a switchable internal noise generator and bypass switch.