Each of the 15 voices has a multimode Filter section. Each filter is disabled by default and can be enabled by clicking the power button in the top left corner of the filter module.
There are three filter modes available: Low Pass, Band Pass, and High Pass. In addition, there is a toggle selector for Gradual and Steep slope control (12 and 24 dB/octave respectively).
The Freq knob controls the filter cutoff frequency. The Reso knob controls the resonance of the filter by boosting the cutoff frequency. You can also click + drag on the filter graphic to adjust the cutoff and resonance (drag left/right to adjust the frequency and up/down to adjust resonance).