[Asterisk-Users] Zap X100P oscillation

[Whisker, Peter]

I find that if I drop the RX gain too much I start to lose DTMF decoding.

The Asterisk calls lose at least 3-6db end-to-end compared with a "normal"
call. If I bring the gain up, the symptoms sound exactly like yours.

The gain I am using is more like Rx=-2, Tx=0 but this is still quite quiet.
I guess that line impedance mismatch between US and European standards
accounts for some of the gain loss.

Peter

-----Original Message-----
From: Mike Benoit [mailto:ipso at snappymail.ca]
Sent: 28 June 2004 21:59
To: asterisk-users at lists.digium.com
Subject: Re: [Asterisk-Users] Zap X100P oscillation


I wonder if your issue and mine are related somehow. 

I have a asterisk server with 4 FXO cards in it, and when a call comes
in one ZAP channel, then dials out another, I hear what could be
described as a steam engine starting up. It starts off kinda slower/
quiet, then quickly (in about 2-4 seconds) completely over powers the
line. 

The only way I could stop it was by adjusting the gains.

rxgain=-8.5
txgain=4

Seemed to do the trick. As did:

rxgain=-6.5
txgain=1

An rxgain of even -8.0 or -6.0 in either case would result in this
"steam engine" sound. -8.5 or -6.5 would make it go away completely.

I'm using a CVS checkout from yesterday, and I tried with both
echotraining=800 and turning echo cancellation off completely. Neither
made any difference.

It would be really nice to be able to use a positive rxgain value. I
haven't tried with the echo app, but using just one FXO card works fine
with almost any rx/txgain value. As soon as the call utilizes two FXO
card at the same time, the "steam engine" sound occurs.


On Mon, 2004-06-28 at 16:26 +0100, Whisker, Peter wrote:
> Has anyone seen this problem before?
> 
> I have a server with a single X100P card. The audio level is a low, but if
I
> raise the gain to more than -2db (Rx + Tx) it starts to oscillate in an
echo
> test. Not at a high frequency but with a noise that is best described as a
> steam engine starting up. It then starts to clip and crackle. If I bring
the
> gain down to Rx=-2.0 and Tx=0.0 or lower then it settles down but it is
very
> very quiet.
> 
> I have tried the latest CVS Head with echotraining=800 set and also
complied
> with the aggressive echo cancelling, but nothing seems to help.
> 
> Ideas welcome!
> 
> Many thanks
> Peter Whisker
> 
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Mike Benoit <ipso at snappymail.ca>

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