I'm not sure where to check next, so I'm reaching out to those that
know this stuff better than I.
I've got Asterisk up and running, but I've still got an occasional
audio issue. Once in a while (maybe 1 out of every 20-30 calls), the
audio becomes heavily distorted, but only on the local side. The party
on the other end says the audio is fine. We can hear them, although on
these calls the remote party is quieter than usual. They can hear us
just fine. But when we speak, our side becomes heavily distorted. It
only happens when we speak. As long as we are not talking, the audio
is fine other than the remote party is not as loud as normal.
The distortion sounds a lot like what a speaker sounds like when it is
blown. Not quite static, not quite feedback, but very crackly and
metallic with pops and squeals. It drowns out all other sound on the
call. We hear it very loud, almost painfully and you have to hold the
handset away from your ear as you talk. The remote party says they
hear nothing at all wrong. It happens on both handset and speaker
phone, so it shouldn't be a speaker issue.
This never seems to happen on interoffice calls, only on calls going
out over our POTS lines. Also, if we put the call on hold or transfer
the call, usually the distortion is gone once the call is picked back
up (although it may come back, but not as bad). Flip side, sometimes a
good call that gets put on hold or transfered will have the issue when
the call is picked up again.
I've done rxgain tuning, although I can't be 100% sure I've done it
right. I followed the advice from
<http://www.mattgwatson.ca/2008/05/howto-tune-zaptel-dahdi-fxo-interfaces-on-asterisk-pbx/
>, but the levels he said to aim for cause me to need to raise my
lines to between +12 and +20 and when listening to the tone on a phone
sound as if they are starting to clip (although that could be correct
for all I know). I had been doing txgain tuning, but in my testing, I
found that either the values I was setting made no difference in the
audio levels or topped out the audio levels around 9000 instead of the
article's recommended 14844. As such, my txgain is currently set to 0
for all lines. Also it is worth noting that I was not able to turn up
a milliwatt test number for my local CO (I even asked a Verizon tech
who claimed they didn't have one in my CO and he didn't know the
number for one in the area, although he may have just been BSing me to
not give it out). The number I used is several states away, so I don't
know how much (if any) audio loss is present on the tone, thus it is
possible my rxgain may be too high for my lines. If anyone knows of a
milliwatt test number for northern NJ I'd be happy to repeat my tuning.
I am using Snom 370 phones (running the latest 7.3.23 firmware, but it
was happening with the 7.3.14 firmware as well). My Analog lines are
connected via a Sangoma A400DE. This is their 12 port card with
hardware echo cancel and PCI-E. The network is a dedicated network,
only the phones are on it, and all are connected to a netgear
10/100/1000 POE switch. The phones are using POE. The only devices on
the network that are not phones are the Asterisk server, a router to
get the network access to the internet (currently outbound only, I've
not yet allowed inbound access to the server) and my laptop for
configuring the server (although the issue happens even without my
laptop connected). So this likely is not caused by traffic killing the
network (won't rule it out, but it doesn't seem like a first guess).
Anyone know what is going on or can tell me where to go next to figure
it out?
Thanks for any
-chris
<www.mythtech.net>
