wah vs svf triggered filter

[idy]

So I realize I'm not clear what I'm really hearing... does a wah sweep a band pass filter across the spectrum, heel to toe? And then a mutron/meatball etc. SVF, in bandpass mode, are we hearing a frequency being swept or is it playing with the gain to a filter that stays at the same frequency? Or are those LDRs changing the frequency of the filter?
Confused.

[ElectricDruid]

Both wahs or mutron/meatball/autowahs sweep a bandpass filter across the spectrum. Sometimes a lowpass filter with a resonant peak is used instead, since it removes less bass and gives a more "meaty" sound.

All the sonic differences come because there are a lot of different ways to do the filter, and many of them don't give the same amount of resonance across the sweep. Some go from high res at low freqs to low res at high freqs, and some do the opposite. SVFs are one of the "keeps the resonance the same" options, and that has a particular sound too. People have built wahs based on inductors, Twin-T circuits, SVFs with OTAs, SVFs with vactrols, etc etc - you name it, it's been tried!

As far as I know, nothing works by altering the gain of the filter (unless that's a side effect) - the *aim* is always to sweep the frequency, and that *is* what those LDRs are doing!

[Mark Hammer]

+1

I will say, however, that some kinds of bandpass filters have an interesting relationship between gain and resonant frequency.  If you increase the feedback resistance in a simple op-amp bandpass, like that used for the Dr. Q, Nurse Quacky, Phuncgnosis,or EHX Bass Balls, you increase the gain (and of course output level), but you also move the resonant frequency  downward.