[Asterisk-Users] UPDATE - Echo cancellation, when software doesn't cut it. Whats next?

[Mike Benoit]

Here's an update on my progress for all who are interested.

After carrying out many more hours of testing, the only thing that made
a significant difference was changing the mainboard/CPU of my asterisk
server.

My original Asterisk server was a Celeron 533 with 128mb ram. Now, keep
in mind, even with 5 channels in use at a time, the CPU usage was always
minimal, the load never went above 0.2 that I saw.

First I upgraded to a brand new Celeron 2.4Ghz with 128mb ram, and
immediately noticed an improvement in the echo. 

Incoming calls now have virtually no echo. I have to really try to hear
it. Outgoing calls still have echo, but after about 30 seconds it mostly
goes away during normal conversation. Still not 100% acceptable though.
However it is a huge improvement. 

The weird part though is this. Outgoing calls to cell phone numbers
(tried 3 different ones) have virtually no echo. Outgoing calls to land
line numbers do seem to have echo. 

I then downgraded my asterisk server to a P3-800 with 128mb ram, and I
didn't notice any difference from the Celeron 2.4. So in my case just
upgrading a Celeron 533 to P3-800 made a noticeable difference, but
anything more than that did not. What I did notice is
in /proc/interrupts, the P3-800 displays:

IO-APIC-level  wcfxo

Whereas I believe the older Celeron 533 displayed:

XT-PIC	wcfxo

So my guess is its not the CPU speed at all, just the way interrupts are
handled.

So the two questions remain. 

1. Why do incoming calls have nearly no echo (sound great), and outgoing
calls are bad during the first 30 seconds, and okay (but not good) after
that. 

2. Why do outgoing calls to cell phone numbers sound great?

Seeing as an outgoing call to a land line has echo, but the same land
line calling in has virtually no echo, does this point the finger at
Asterisk code having issues?


On Wed, 2004-06-30 at 16:36 -0700, Mike Benoit wrote:
> Over the last couple weeks I've tried everything I could get my hands on
> in an attempt to get rid of my echo problems. Using a CVS checkout of
> just yesterday, I've tried every echo cancellation routine in zconfig.h
> (including Mark2 w/Aggressive) , as well as the echotraining=800
> mentioned on this list just last week. 
> 
> While some things worked better then others, I would consider none
> acceptable solutions in my situation. Playing with rx/tx gain values
> just seemed to quiet the voice down and along with that the echo
> happened to be less noticeable. I could almost get the echo to disappear
> with a low enough rx/tx gain, but then the voice could barely be heard,
> or DTMF tones stopped working.
> 
> So whats the next step? 
> 
> I only get echo when dialing over the PSTN. Using Nufone to dial a PSTN
> number results in absolutely zero echo. Do I put in a request for a
> Telco technician to come out and take a look at the lines? 
> 
> One page on the Wiki says:
> 
> "Most of the telco's have technicians with the equipment necessary to
> help find the problem if the problem really is their outside plant.
> However, getting to that person can be a real challenge."
> 
> Any suggestions on ways to overcome the challenge of getting the right
> technician on the phone? 
> 
> Thanks.
> 
-- 
Mike Benoit <ipso at snappymail.ca>