Call Recordings channels out of sync


Firstly apologies if there is an answer to this posted somewhere already, if there was my quick search didn’t find it but I’m new to Asterisk and may not be using the right terminology in the search.

I’ve been asked to look at a problem where voices are out of sync in a call recording. This is on Asterisk 1.2.13 (this is production so I can’t just slap the latest version in in the hope that the problem will go away) which is recording 2 half-duplex uLaw files which are merged externally (soxmix) to create a gsm file.

As far as I can tell one or other of the channels (it varies) is loosing data (based on the differing file lengths which always differ by a multiple of 160 bytes) I’m seeing differences of 1 to 50ish packets.

This appears to be causing time compression on one channel when they are mixed leading to the out of sync condition.

One channel is always VOIP the other could be either VOIP or POTS. neither the zaptel (TE405P/TE410P) card or the network is showing any indication of dropped packets, missed IRQs etc. so at a hardware level appears to be fine (as far as I can tell) which suggests the problem may be in Asterisk it’s self

Can anybody suggest how to start tracking this issue down, anything to help me get an handle/start point on it would be appreciated.

Again apologies if this is already answered but I’m parallel processing the research to save time.



This seems to be a tough one. I am a bit tired to look for an answer now. Try the asterisk users list ( or #asterisk on