This is only the tiniest bit related to crypto, but that doesn't seem to be much outside the criteria for submissions to this list.. :-) 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.) thx. -- J. Eric Townsend jet@nas.nasa.gov 415.604.4311 NASA Ames Numerical Aerodynamic Simulation | play: jet@well.sf.ca.us Parallel Systems Support, CM-5 POC | '92 R100R / DoD# 0378 PGP2.1 public key available upon request or finger jet@simeon.nas.nasa.gov
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
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.
you can do two FFT's by using the fact that: FFT( x(t) + j y(t) ) = Z(w) then X(l) = 1/2 ( Z(l) + Z*(N-l)) and Y(l) = 1/2j (Zl) - Z*(N-l)) Where x(t) <-> X(w) y(t) <-> Y(w) N is the length of both arrays j is sqrt(-1) Z* is the conjugate of Z (a+jb <-> a-jb )
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Eric Hughes -
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Timothy Newsham