[asterisk-users] DTMF tones in MixMonitor recording

Joshua Colp jcolp at digium.com
Tue May 1 04:34:56 CDT 2018

On Mon, Apr 30, 2018, at 11:23 PM, Patrick Wakano wrote:
> Hello list,
> Hope you are all doing fine!
> I have stumbled over some piece of dialplan code in which apparently they
> were trying to avoid recording the DTMF tones in the wav file. It is really
> messy and I am not sure if this really works. So after a bit of research I
> found this comment (
> https://community.asterisk.org/t/asterisk-dtmf-record/65040) in which it is
> said:
> *"Asterisk strips the DTMF from the audio stream when configured for
> inband, so internal stuff can react to the DTMF and so the other side does
> not hear the tone unless they are using inband (in which case it is
> regenerated)"*
> So my questions are, what are the cases in which Asterisk regenerates the
> DTMFs? Does it cause the recording to have the tone as well, or is it only
> transmitted to the other leg without being generated to the recording file?
> Also, what if one or both legs are RFC2833? From my tests the RFC2833
> events never show up in the recording, but I just want to confirm that this
> is always true.

If properly configured then Asterisk will always strip and regenerate the DTMF tone. You have to purposely misconfigure things to cause it to not get stripped. IE: DTMF is actually inband but you configure it for RFC2833. Since Asterisk wouldn't be listening to the audio stream, it would go right through and get recorded.

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

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