lkml.org 
[lkml]   [2003]   [Jan]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Asterisk] DTMF noise
Mark Spencer wrote:

> The DTMF detector in the linux kernel is fairly simplistic and doesn't do
> many relative energy tests. The Zapata library has a much better tone
> detector, but it is FP, and so would have to be made fixed point. If
> nothing else, it may provide some lessons for the ISDN folks.

I remember that a good DTMF decoder can be very simplistic: DTMF was designed
for that.

The idea is:

- separate the high tones from the low tones.
- amplify clip the high band and the low band separately
- run the tone decoders on the clipped signals

The clipping stage would make sure that only relatively pure tones will trigger
the detector.

See also http://groups.google.com/groups?selm=7462%40accuvax.nwu.edu


Thomas

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:32    [W:0.087 / U:2.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site