After a recent experience at a hall with a resonant frequency which doubled my volume near B/C, I've thought about getting a pedal with a variable notch filter to hunt down the offending frequency. A variable Q seems useful and of course attenuation level of the filter. Seems I don't encounter this situation enough to really worry about it or make too much of an investment. Too bad I got rid of the beringer DEQ I had.... While I'm at it may as well have a variable HPF thrown in. Anybody know of an analog pedal or circuit plan with this functionality?