asterisk users - Jan 2006 - DTMF Simultaneous Inband and RFC2833 performedby Asterisk => Duplicate tones

> I have seen the following effect in Asterisk, though:  where 
> it converts 
> an inband DTMF (eg coming off a Zap channel) into an 
> indication, it mutes 
> the audio where that tone is.  But sometimes it leaves a 
> teeny bit of the 
> tone behind.
> 
> If you take such a call over say IAX to somewhere and then 
> back out a Zap 
> channel, you end up with the teeny remaining bit of the 
> original tone, 
> PLUS the regenerated tone.
> 
> If you are very unlucky a remote DTMF receiver can hear two digits.
The same thing can happen when a SIP "ATA" is configured to 
use rfc2833 but is also a little to lote with the filtering 
out of the DTMF. So sometimes it's not Asterisks fault at 
all ;-)

And then there's some IVR's that don't notice it at all, while
others
are totally unusable.


-- 
Andreas Sikkema                       BBned NV
Software Engineer                Planeetbaan 4
+31 (0)23 7074342            2132 HZ Hoofddorp

On Thu, 19 Jan 2006, Andreas Sikkema wrote:
> The same thing can happen when a SIP "ATA" is configured to 
> use rfc2833 but is also a little to lote with the filtering 
> out of the DTMF. So sometimes it's not Asterisks fault at 
> all ;-)
> 
> And then there's some IVR's that don't notice it at all, while
others
> are totally unusable.

Obviously we can't do anything about the ATA.

But I did have an idea for Asterisk...

Which is that when the DTMF detector spots DTMF in an audio frame, that it 
passes along on the channel a kind of "merged frame" which is both the
detected DTMF AND the actually audio.  Then, when the frame arrives at an 
application of a channel that wants the indication, it can use that.  On 
the other hand, if the frame arrives at a channel that needs to send 
inband DTMF, the indication can be ignored and the original audio passed 
on instead.

Steve