[Asterisk-Users] Echo and crackle

[Joshua West]

Crackling is usually a sign of IRQ issues, as Mojo wrote.  Digium's full
documentation on solving IRQ issues are here: 
http://www.voip-info.org/wiki/view/Asterisk+PCI+bus+Troubleshooting

Regarding echo on POTS lines, I wish you the best of luck.  Fixing your
IRQ problems may reduce the delay enough that echo will not be noticed,
but we were unable to do just that with our previous system's
configuration (13 POTS lines).  After extensive testing, we finally
moved over to a T1 (ESF .. not an ISDN PRI).  Unfortunately, we still
experienced echo when calling or receiving calls from people/systems
using analog telephone lines.  Implementing a Ditech Communications
SX-24 T1 echo cancellation module inside the Gemini-T shelf solved our
problems.  Adios echo, no more users upset, etc.  This unit is however
no longer available from Ditech Communications
(ditechcommunications.com) as the product has gone end of life.

I recommend doing your best to remove the crackling first as the cause
of crackling could be also affecting echo.  There have been some people
reporting results of getting rid of echo on POTS lines by just tweaking
Asterisk/Zaptel.

If you get stuck on solving echo - or find its really hard to determine
if echo still exists - let me know.  I have a lot of good tricks up my
sleeve regarding exact measurement of echo using free software and a
little bit of analysis (with pretty pictures etc).  I should probably
put this info on the voip-info.org wiki... hmm...

-- 
Joshua West
Linux Infrastructure Engineer
Boston Engineering Corporation
http://www.boston-engineering.com



Mojo with Horan & Company, LLC wrote:
> I will agree that switching to the TDM card significantly helped my
> echo and sound quality, I would take a second to point out that
> interrupt sharing on your * server might cause crackling-like noises. 
> Try
>
> lspci -vb
>  and
> cat /proc/interrupts
>
> to see if you discern any hardware using the same irq the x101p is.
>
> Also run zttest in the zaptel source directory and see what the
> average number is.  s/b 100%, but I believe as low as 98% or
> thereabouts should have pretty acceptable call quality.  If it dips
> even lower than that regularly, or concurrently with the crackling
> sounds, then your server is probably working too hard on irrelevant
> processes or has irq sharing issues.
>
> Moj
>
> M.Hockings wrote:
>> We are running asterisk with a single POTS line for local calls and a
>> voip line for long distance.  Whenever we receive a call on the POTS
>> line it is more than likely, but not always, going to have
>> significant distracting echo.  In addition to that there is
>> occasional heavy crackle or static.  I have tried to follow the
>> guidelines at :
>> http://www.voip-info.org/wiki/view/Asterisk+echo+cancellation
>> but it does not seem to have made much difference.
>>
>> Currently we are using a X101P for the POTS line and a TDM401B
>> (TDM400P with one FXS port) for the conventional telephones.  From
>> what I have read, it may help to use an FXO port on the TDM400P
>> rather than the X101P for the POTS line.
>>
>> What is the "conventional wisdom" about the echo in this
>> configuration and what causes the crackle and how should I tackle
>> that?  I have tried rebooting/power-cycling the machine to reset the
>> hardware but it really hasn't noticeably helped.
>>
>> Is there anything else that I can try?
>>
>> Thanks,  Mike
>>
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