I'm not sure what level you're looking for, but I found this really good: http://www.mikeash.com/pyblog/friday-qa-2012-10-26-fourier-transforms-and-ffts.html ht

I'm not sure what level you're looking for, but I found this really good: http://www.mikeash.com/pyblog/friday-qa-2012-10-26-fourier-transforms-and-ffts.html http://www.mikeash.com/pyblog/friday-qa-2012-10-26-fourier-t...