> My project uses a PIC12C509 to monitor sensors and then outputs various
> simultaneous tones.  The tones are recorded on audio tape using a compact
> cassette recorder.

You may be able to save yourself some trouble if you record DTMF tones (if
that is enough) and then play it back through a DTMF decoder. You may be
able to find something on the web that will decode DTMF tones directly from
a .WAV file.

> Can anyone tell me the
> principles of software filtering or point me to web sites that may help?
I
> also need to know  about the file format of a WAV file. Can anyone help
> please?

For .WAV files; If you want lots of words, look for "Multimedia Programming
Interface and Data Specifications 1.0" by IBM and Microsoft. I think I got
it from Microsofts web site. If you want it in a simpler form, try
http://www.lightlink.com/tjweber/StripWav/Canon.html. It is a pretty simple
file format.

For learning DSP (now you're in the deep end), try
http://innet.com/~condor/wghome.html as a starting point and follow a few
links.

Steve.

======================================================
  Very funny Scotty.  Now beam down my clothes.
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680                email: steveb@kcbbs.gen.nz
New Lynn, Auckland           ph  +64 9 820-2221
New Zealand                  fax +64 9 820-1929
======================================================