Voice echo

Unanswered Question
Aug 8th, 2007

I have a 2801 with a PRI card in it that is connected to a Telerad PBX. There are 12 voice channels setup and about 20 phones hanging off of the PBX.

The problem is that occasionally you hear the echo of your own voice for about 2-3 seconds then everything is fine. Then a minute or so later it will happen again.

There does not seem to be any pattern to it, and there can no other calls up or a bunch.

The echo happens only on the PBX side, not on the PSTN side.

Any ideas where I should start looking?

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hadbou Thu, 08/16/2007 - 06:04

Try any of these:

1) Reduce the level of the signal on output from the gateway to the PSTN by using a positive output attenuation value.

2) To reduce the level of the echo, use a negative gain on input to the gateway from the PSTN.

Increasing and decreasing signal levels affects the volume of the main signal as well as the echo. Ensure that you increase and decrease levels in small increments.

a.cruea1980 Thu, 08/23/2007 - 09:24

So you hear the echo, not the people on the other end of the line, right?

What you might try doing is tweaking the echo-canceling values first.

The thing to do is get a 7960 IP phone, call one of the numbers that IS echoing, use the 7960 to generate the testing tone, and go from there. Playing with your attenuation before you've identified a solid problem is a bad, bad, bad, bad, bad idea.

http://www.cisco.com/en/US/products/sw/voicesw/ps1860/products_tech_note09186a00800b4a71.shtml

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtml

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml

Before playing with attenuation, make sure your impedence on the lines is set properly, make sure your users really aren't echoing from the ear piece to the microphone, stuff like that.

If you're only hearing echo for about 2 to 3 seconds, though, it sounds like your echo-canceller just needs tweaked, because it is converging on the echo properly, just not fast enough.

davecisco Mon, 08/27/2007 - 08:25

The client calling the PSTN is hearing their own voice echo back to them. PSTN hears and sounds fine to the client.

The system is not using Cisco phones with CM, they have a 2801 router with a PRI card hooked up to a Telrad PBX.

So the fact that they are echoing back to them selves does that may you think that is it local to the PBX?

Thanks for the response I will look at the echo canceler.

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