[Freeswitch-dev] Detecting in-band DTMF Digits in Openzap?

Moises Silva moises.silva at gmail.com
Thu Aug 20 10:03:30 PDT 2009

I discussed with Mike Jerris some days ago, and as I pointed out we need to
be able to tell the duration of the DTMF. At this point libteletone does not
help with that (AFAIK), so we need to investigate and fix it. Just haven't
found the time to do it. Help is welcomed :-)

On Thu, Aug 20, 2009 at 1:58 AM, Alex Green <alexg at etherstack.com> wrote:

> Any thought on the email below? I would imagine that passing an analog
> call through freeswitch is not too uncommon a use-case...
> >     4.: Potential bug:
> >     DTMF digit detection *eats some audio* each time a digit is detected.
> If
> >     the device is connected directly to free switch this is not a
> problem.
> >     If a device makes a call through freeswitch (to let's say phone
> banking)
> >     a digit that is held down may be detected as 3 digits (sometimes
> more)
> >     due to the consumed audio. This can be heard on the other side of
> >     freeswitch as a start-stop at the start of the DTMF.
> >
> >
> > Indeed ZAP_CHANNEL_SUPRESS_DTMF causes zap_channel_read to memset the
> > read data each time a digit hit is found. The problem is that there is
> > no DTMF_START and DTMF_END events and the DTMF length is lost, we just
> > have a plain DTMF event for the start. Not sure about how to use
> > libteletone to detect the DTMF end though.
>  >
> DTMF suppression is mangling the digits.
> It took me a while to get to the bottom of this, but it turns out to be
> very easy to reproduce. Take Freeswitch with an FXS port and a handset.
> Dial 1000 on the handset and answer the call on a SIP client. Now hold
> down a digit. You will notice that the digit has a wobble at the start.
> This is the symptom.
> Commenting out the DTMF suppression code, changes the behaviour but does
> not fix the problem. This is what baffled me for a while. I wrote some
> trivial code that bridges two analog channels by doing a
> zap_channel_read/write() from one to the other. Commenting out the
> memset() on line 2042 of zap_io.c produced perfect digits while
> uncommenting it produced the wobble. The obvious conclusion is that the
> dodgy digit suppression is being attempted somewhere else (like the SIP
> side?) and thus the wobble is being introduced at more than one place.
> This also explains why I (non scientifically) noticed that the more
> times the call passed through Freeswitch the more incorrectly recognised
> digits were reported at the final point.
> I imagine that a solution might be to just turn off DTMF digit
> suppression by default until it is fixed.
> Cheers, -alex
> > Anthony, Mike? care to comment about this one?
> >
> > --
> > Moises Silva
> > Software Developer
> > Sangoma Technologies Inc. | 50 McIntosh Drive, Suite 120, Markham ON L3R
> > 9T3 Canada
> > t. 1 905 474 1990 x 128 | e. moy at sangoma.com <mailto:moy at sangoma.com>
> _______________________________________________
> FreeSWITCH-dev mailing list
> FreeSWITCH-dev at lists.freeswitch.org
> http://lists.freeswitch.org/mailman/listinfo/freeswitch-dev
> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-dev
> http://www.freeswitch.org

Moises Silva
Software Developer
Sangoma Technologies Inc. | 50 McIntosh Drive, Suite 120, Markham ON L3R 9T3
t. 1 905 474 1990 x 128 | e. moy at sangoma.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.freeswitch.org/pipermail/freeswitch-dev/attachments/20090820/b9447dcb/attachment.html 

More information about the FreeSWITCH-dev mailing list