I recently filmed a live performance where there was a 45 second interval of feedback from one of the microphones during one of the songs. When I went to try to remove the feedback squeal during post production, it took me a long time to find the frequency of the feedback sound. I basically kept trying a digital notch filter at various frequencies until I found a frequency where the feedback started to be diminished. Once I was close, it still took me a while to hone right in on the exact frequency so that I could notch it out. This process would have been much easier if I had a spectrum analyzer that would have allowed me to see the frequency of the offending signal. I'd want one that could look at a .wav file and give me the amplitudes of the various frequencies in the interval of interest. Does anyone have a recommendation for some software that provides this function? Or another recommendation for how one would solve this problem?

Bias' (http://www.bias-inc.com/) SoundSoap might make the job a bit easier if you are a Mac and Peak user. (A stand-alone Mac OS-X version is promised.)

For PC users, Sound Forge has a spectrum analyzer.

I've used SoundSoap and found it very effective at removing all kinds of extraneous repetitive noises.