Hi,

I am trying to implement an IVR functionality as a part of Windows
application. I don't want to use TAPI.

So, I am looking for a source code detecting DTMF signals within a PCM
audio stream.

Can anybody help me on this? Any references?

Thanks in advance,
Mark

m...@mail.com (Mark) wrote in message news:<a...@posting.google.com>...
> Hi,
> 
> I am trying to implement an IVR functionality as a part of Windows
> application. I don't want to use TAPI.
> 
> So, I am looking for a source code detecting DTMF signals within a PCM
> audio stream.
> 
> Can anybody help me on this? Any references?
> 
> Thanks in advance,
> Mark

To demodulate multiple tones, you need to use a simple FFT.  This can
be done by analyzing only the real part of the signal for instance. 
You will find plenty of info at www.analog.com or www.ti.com.  The
first step however, is to linearize the data and undo any Mu or A law
encoding.

Cheers,

Herman
http://www.AerospaceSoftware.com

m...@mail.com (Mark) wrote in message news:<a...@posting.google.com>...
> Hi,
> 
> I am trying to implement an IVR functionality as a part of Windows
> application. I don't want to use TAPI.
> 
> So, I am looking for a source code detecting DTMF signals within a PCM
> audio stream.
> 
> Can anybody help me on this? Any references?
> 
> Thanks in advance,
> Mark

Here are some references on the Goertzel real mode FFT:
http://www.isip.msstate.edu/conferences/dsp95/paper_dtmf.pdf
http://www.embedded.com/story/OEG20020819S0057

You can also find PCM Mu/A law and DTMF schtuff on my site here:
http://www.aerospacesoftware.com/contents.htm

Cheers,

Herman

Thanks, Herman.
Your answer was very helpful.

Mark