Fomp is an LV2 port of the MCP, VCO, FIL, and WAH plugins by Fons Adriaensen. The auto-wah, is basically a combination of an envelope follower and a resonant lowpass filter. For increasing level both the frequency and the bandwidth of the filter will increase. How much is controlled by 'Drive'. For a normal wah, use a pedal to control 'Frequency' and set 'Drive' to zero.