On 13 Mar 2007, at 00:32, David Brazier wrote:
Hi All
I have a problem with IVR scripts which consist mainly of Playback of
audio files, driven from an AGI application. There are clicks
every few
seconds or more frequently that is audible on the remote end
(PSTN), but
not on the Asterisk recording of the call. If I record the remote end
and compare it to the local recording, it appears to be about 5%-7%
too
fast - i.e. if I synchronise the starts, the remote end finishes
sooner.
I can find points in the remote recording where parts of the waveform
have been missed out, leading to jumps in the waveform, which
correspond
to the audible clicks. These "jumps" seem like dropped packets,
and I'm
deducing that Asterisk is sending data slightly too fast (i.e. more
frequently than 50x160 sample per second) for the remote end, which
has
to drop data to keep up.
This is a VoIP-only set up - no Zap hardware. Thinking this was a
timing issue, I have installed Zaptel to get ztdummy, which is loaded
OK, but that hasn't made any difference. I have tried it with
different
VoIP providers and observed the same problem.
Behaviour has persisted from 1.2 to 1.4 and now 1.4.1. CentOS 4.4
(2.6.9 kernel), Dell 1950.
Any ideas how to progress? Is this a timing issue or am I wide of the
mark?
Thanks for any help
David
It would be interesting to see an ethereal trace of the packets going
to your PRI gateway. Ideally the packet capture would be done by
a separate system, so that the clock of your Dell won't also be the
'reference' clock.
Do you run NTP on that system. If you do, take a look at the
skew over a day or so and see if the Dell is running fast.
It might be worth investing in a low end digium card
just to generate a clock that is independent of your CPU
clock.
Tim Panton
www.mexuar.net
www.westhawk.co.uk/
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