The "Dual Filter" is not, simply, a stereo multi-mode filter, in the conventional sense. The "left" filter channel and the "right" filter channel are not treated equally, which might cause some confusion, initially. What does this all mean?
1) The "right" filter channel's cutoff frequency control is multiplied from the "left" channel's cutoff frequency using the "Dual Mod" and "Mod Range" knobs. The "Dual Filter"'s "Cutoff" knob will then sweep through the left and right channel frequencies, but with the right channel's frequency augmented by the multiplier's controls (again: "Dual Mod" and "Mod Range"). Experimentation with these controls will soon give you an impression of what this device is all about.
2) What is this device all about? The "Dual" bit of this device is what makes it special. By shifting the left and right frequencies away from each other, a spatial aspect to any input-sound can be achieved, in tandem with the device's filtering properties. The sonic result is somewhere between a filter and a stereo phaser. The "Dual Filter" will give you a new and unique tool to mutate your sounds with. It can be smooth and subtle, or harsh and distinctive.
3) Each of the devices's three filter-types can be mixed freely with the others, including: lowpass, highpass, and bandpass. In addition, there is a "Crossfade" control that flips the Left to Right and Right to Left channels.
4) Although a filterbank at its heart, the "Dual Filter" really needs to be "played" to enjoy is full sonic potential. It has been designed to be performed on, like a synthesizer without its own oscillators... in this way one can control the filter's envelope, LFO triggering, keyboard following, velocity, and aftertouch, using a MIDI-controller keyboard. Use an SFP synth, or sampler-module, in the usual fashion and then plug the synth/sampler's output(s) into the "Dual Filter"'s inputs... you can then match the "Dual Filter"'s MIDI-channel with the synth/sampler's MIDI-channel, thus the "Dual Filter" becomes an extension of the original sound-source module.
5) The "Dual Filter" can also be used as a stereo effect insert, or as an XTC plug-in, in your favorite VST-compatible software. However, functionality, in these modes, is limited to the direct filter control knobs and the LFO because there is no MIDI-keyboard control possible. The functioning surface parameters can still be automated in the usual fashion.