David Caldwell wrote:
> Thanks to everyone for all your feedback regarding echo. Here's some
> feedback:
>
> Kris: My cable length from the analogue PTSN socket to the TDM400 is
> about 15-20m. I should be relocating the Astlinux server today which
> will cut the cable run down to about 2m.
>
> Yes, I'm in the UK and I'm initialising the TDM using zaptel.conf with
> the following entries: fxsks=1-6, loadzone=uk and defaultzone=uk. All
> the modules on the TDMs (I've got two with a total of six modules) are
> FXO (ie: accepting PTSN inbound) although I've only actually got one
> line out of six plugged in at the moment for testing. I don't know where
> I can alter the impedence setting if it's not automatically done when
> zaptel.conf is read - can you tell me where I do that?
>
> Thankyou for the link to ztmonitor. It works a treat after altering the
> permissions on it.
>
> I'll download and experiment with version 0.4.1 as soon as I get time.
>
> Canuck15: Yes, hardware echo cancellation is something we may consider
> if we can't improve the echo to everyone's satisfaction.
>
> Nik Middleton: I have also considered the handsets. I guess getting
> cheap handsets for testing is a false ecomony. However, the handsets we
> got (2 x Grandstream 102, a Zyxcel Prestige 2000 ATA with two old
> analogue phones connected and a Zyxcel wireless handset over a D-Link
> WAP) had good reviews from many people so we thought they'd be a safe
> bet. Still, handset quality (both ours and the remote end) is obviously
> a very, very important factor.
>
> Michael Knill: Yes, it had crossed my mind that if we are hearing echo
> then it must be caused at the far end. It's also crossed my mind that my
> cable run of a measly 15-20m is nothing compared to the run to the local
> exchange, etc. However, I want to rule out our internal cabling out of
> principle.
>
> Thanks for the link to the Cisco document - superb! Wish I'd seen it
> sooner...
>
> I've played with the gain levels and seen some improvement - but it
> seems to be a fine line (and a not always a compatible line at the
> moment) between clarity of call and loudness of echo. With ztmonitor
> kindly provided by Kris, this should be little easier to tweak now. I've
> set the gain and echo setting back to defaults for now.
>
> Wow! you guys have given me a lot to go on! I hope to have time to do
> some more testing soon - I'll let you know how it turns out.
>
> Have a good weekend,
>
> David.
>
David,
Try modprobe'ing wctdm like this:
modprobe wctdm opermode=UK
That should set the card to the proper impedance for the UK.
P.S. - I agree totally with the comment about the handsets. Most echo
can be traced back to improper gain settings in the handset...
--
Kristian Kielhofner
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