non-cypher related question on audio analysis

[Eric Hughes]

>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