non-cypher related question on audio analysis

Anyone got pointers to decoding audio tones? An intro book, source code, newsgroup, mailing list, somebody I can take to lunch? I'd like to sample audio with my SGI, and suck out various simple tones and combinations of tones. (DTMF, single pitch variant tones, etc.)

I've got a good book on DSP by Rabiner and Gold. There are a few DSP newsgroups where the local experts hang out. Also the modem design groups. After you know something, remember this: The FIR filter is the same mathematically as a FFT, multiplication by a filter window function, and an inverse FFT. As I recall, you can process multiple FIR's in parallel. All the DSP manufacturers come with lots of example source code for standard filters (FFT, FIR, IIR, etc.). Eric