This is possibly more of linux-isdn@vger.kernel.org list thing,
than linux-kernel per se.
On Thu, Dec 12, 2002 at 11:45:26AM +0100, Roy Sigurd Karlsbakk wrote:
> hi
>
> it seems isdn4linux detects DTMF tones from normal speach. This is rather
> annoying when using i4l for voice with Asterisk.org. This is tested on all
> recent kernels
>
> see thread "[MGCP] Asterisk/D-Link phones generates ugly DTMF tones!!!" at
> http://www.marko.net/asterisk/archives/ for more info.
Quick reading of drivers/isdn/isdn_audio.c(*) shows that it does use
fixed-point Görtzel (Goertzel in english) algorithm for detecting
tones, but it does _not_ do comparison of received overall signal
power vs. detected DTMF tone powers.
When there is signal power outside the DTMF channels, signal should
not be detected. Also, DTMF tone powers should be roughly equal,
and exactly two tones should be present for valid detection.
http://www.numerix-dsp.com/goertzel.html
Adding those power tests should be fairly trivial, but I leave it
to Somebody Else...
(*) kernel version I looked upon was 2.4.16-0.11custom -- some RH kernel
> roy
> --
> Roy Sigurd Karlsbakk, Datavaktmester
> ProntoTV AS - http://www.pronto.tv/
> Tel: +47 9801 3356
/Matti Aarnio
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This archive was generated by hypermail 2b29 : Sun Dec 15 2002 - 22:00:24 EST