I like to use white noise (file in first post), since it is a more consistent signal than any guitar playing.
I match the heel and toe positions and then the reduction of resonance seemingly all wah pedals have in the high register. I mostly use my ears, but also use a spectrum analyser to confirm.
Yeah, whatthehell i'll give it a try this weekend!
Yes resonance has to dip towards the opening of the filter to sound right i guess to not peak through like an ice pick (mental image of moog filter in head :-))