[asterisk-users] MixMonitor inserting extra 20ms packets of silence (1.4.43)

Tony Mountifield tony at softins.co.uk
Mon Sep 10 11:13:54 CDT 2012

I'm trying to diagnose potential causes of an issue with MixMonitor in 1.4.43
(I doubt it's very version-specific). I won't have hands on the kit until the
end of the week, but I have listened to some recordings. It doesn't happen on
every call - only sometimes.

Basically, it is a call from one SIP phone extension to another, and the
dialplan sets up MixMonitor on the calling channel before doing the Dial.

The call sounds fine to both parties in the call, but when listening back to
the recording, the speech is slowed down and broken - a bit like a robot or
dalek voice. Examining the recorded audio in Goldwave I can see that every 20ms
(the size of a SIP packet), an extra 20ms of silence is being inserted in the
recording file. This happens most of the time, punctuated by occasional bursts
of clear audio before it starts happening again.

Has anyone seen this kind of thing before? Better still, seen it and solved it?

The "SIP phones" are actually Soundwin ATAs.

There is no zaptel or dahdi timing source in the system.

Are there any known issues with MixMonitor that could cause this behaviour?

Any pointers would be appreciated - thanks!


Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

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