[asterisk-users] Echo issue

[CunningPike]

On Tue, Dec 8, 2009 at 7:37 AM, Noah Miller <noahisaacmiller at gmail.com> wrote:
> Hi -
>
>> I am having echo issues on our Asterisk box using a PRI circuit.  I was
>> using the software echo cancellation and that helped a bit but didn't solve
>> it completely.  So I went and bought a Digium echo cancellation module for
>> the TE121 card.  That made it even worst, getting more echo on external
>> calls and between internal extension to extension.  The echo doesn't happen
>> all the time, but enough to get complaints from our users.
>>
>> Completely fed up with the issue, I removed the module from the card.  Can
>> someone guide me on how to fix/tune/address the echo issues.
>
> You can likely eliminate most echo on a PRI by setting txgain and rxgain.
>
> Are you using dahdi or zaptel?  If Dahdi, what do your system.conf and
> chan_dahdi.conf look like?  If zaptel, what do your zaptel.conf and
> zapata.conf look like?
>
> When you say you have echo on calls that are internal extension to
> internal extension, are the endpoints using dahdi/zaptel or some voip
> technology (sip, iax, mgcp, skinny, etc)?  If voip, any echo is
> acoustically generated by the endpoints themselves.  On voip calls
> I've often had this happen when the endpoints are using headsets, or
> have gain levels set very high.
>
>
> - Noah
>

We found ourselves in a similar situation during our rollout and
solved it with a quad-span Ditech echo-cancellation appliance
(http://www.ditechnetworks.com/products/quad-2_echo-canceller.html).
It's a couple of grand, but after months of playing with software EC,
the hardware modules and every zaptel setting we could find, this
appliance removed echo like flipping a switch. The metrics we later
obtained from it clearly showed that we simply had tail on a long loop
to an old CO switch that exceeded the maximum 128ms that either
software EC or the hardware module could handle.

The side benefits are that we get all sorts of metrics from the
appliance, and we also get adaptive gain, which solved another problem
we had with trying to find gain settings that suited both
softly-spoken and strident users. The support from Ditech was
excellent and we haven't looked back.

CP