[Freeswitch-users] Choopy one-way noise

[Christian Benke]

Hello!

On a box with a Sangoma A500 BRI card i have a serious audio quality
problem. The "outside"-leg of a call hears a choppy robotic noise,
it's difficult to understand the actual voice. I hope someone
recognizes this issue, as i have tried several approaches and so far i
neither know what causes the problem nor where it is caused exactly.

Here's a sample file(The noise is not very noticeable, it's the
oscillating hum you hear in the background, the short voice-sample you
hear is mine, but it's inbound so it's not affected):

http://poab.org/test1.wav

If the call is set on-hold or if there's a playback/moh, the quality
for the outside-leg is fine while there's no two-way-audio, so my
assumption was that it's some kind of problem with codecs or
transcoding. Capturing the RTP-Stream from the phone to the server
proved though that the quality is fine before it arrives at FS(There
are no audio problems on internal calls as well).

Here's what else i've tried without success:
- set disable-monotonic-timing to true
- started FS with the -rt Flag(As well as -waste and -heavy-timer)
- jitter "time_test" 100 100 responds with avg 130(Thats fine right?)
- rearranged the codec-settings of the phone(Sangoma SPIP 450) to give
A-law the highest priority
- high-precision-timer is available in the kernel according to dmesg
and /proc/timer_list (kernel is 2.6.32-5-686 on debian 6.0)

Sangoma's Support appears to be clueless as well, they didn't have
effective suggestions so far(Opened a ticket 2 weeks). Since i don't
have this problem with identical hardware without
Sangoma-Cards(SIP-Trunk instead), my first assumption was the card.
Probably an interrupt issue?

Any suggestions would be highly appreciated, i'm a bit at loss now and
only know more drastic next steps(Replacing ISDN-Modules or the whole
hardware).

Best regards,
Christian