[asterisk-users] ConfBridge dtmf_passthrough=no doesn't have any effect. Bug?

Joshua Colp jcolp at digium.com
Fri Sep 28 10:33:02 CDT 2012

Markus wrote:
> Hi Joshua,


>> My suggestion is to take a step back further.
>> Just send incoming calls to the Read application and have it store the
>> received DTMF in a variable. Next step have it output what was received.
> Ok, good idea, here are the results of Read() and SayDigits():

<snipped results to make this email manageable>

How are you changing the DTMF for each provider? If you are merely 
changing it using dtmfmode in sip.conf this may or may not change how 
the provider side sends it. In the case of setting it to rfc2833 it 
causes RFC2833 to be negotiated in the SDP. Some equipment MAY change to 
using inband if it has not been negotiated.

>> If that works for all cases then Asterisk is recognizing DTMF fine. This
>> does *not* mean that the tone will be muted fully as my previous email
>> mentioned.
> I don't see any previous eMail from you on the list and there is nothing
> in the archives either. Could you re-send it, please? Maybe the info
> that I'm missing is inside that mail. :)

I think I wrote the email in my head, oops.

Essentially when doing conversion of inband DTMF to out of band DTMF it 
is possible for some parts of tones to get through unmuted. You have to 
strike a balance between detecting the DTMF early enough, not detecting 
other stuff as DTMF, and muting it. Some implementations may let some 
"leak" through. The only way to completely overcome that is to buffer 
enough audio and delay the stream.

>> You can further test if all cases check out by sending calls to Record
>> and playing back the audio to yourself. If you hear tones and Asterisk
>> also recognized the DTMF then it's not fully muted, or the hardware in
>> question is sending *both* inband and out of band, which is not
>> supported.
> Ok, here are the results of Record() and Playback():

<snipped results again, can be viewed in mailing list archives if anyone 
is curious>

> If I understand right, all my four DID providers are "broken"?

If the provider is doing the conversion their equipment should mute the 
inband DTMF as best it can and you should not hear it.

How much of the tone are you hearing?

Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at:  www.digium.com  & www.asterisk.org

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