[asterisk-dev] Adding Octastic Soft-Echo to external SIP adapters

[Eric "ManxPower" Wieling]

critch wrote:
> On Mon, 2007-05-07 at 19:54 +0500, Vazir wrote:
>> PSTN (MY CALLING CARD CUSTOMERS) <---> CISCO AS5350 <---> 
>> VOIP SIDE (SATELLITE ~600mc roundtrip - 300 mc oneway!)
>>
>> So the echo is generated by the VOIP side. I can hear it 
>> very well is I switch off echo cancellation on the CISCO
> 
> If you hear the echo, it was produced on the other end. You audio went
> out and came back. So assuming you are on one side and your customers
> are on the PSTN, the echo happened on the PSTN and is supposed to be
> cancelled by the cisco before becoming voip. If you turn off the echo
> cancel on the cisco, it just digitizes what came back on the wire and
> sends the echo and all to you.

I usually explain "VoIP" echo like this:

When you are talking and in a small room you do not hear echo.  The echo 
is there, after all your voice is bouncing off the walls and coming back 
to you.  However, because the delay between you hearing your voice and 
the sound being bounced back off the walls is so short you do not 
actually perceive the echo.

When you are in a large room and are talking you hear echo.  There is 
NOTHING different about being in a small room .vs. a large room with 
regards to echo EXCEPT that in a large room the delay between you 
hearing your voice and you hearing the sound reflected from the walls is 
much greater and so you perceive the echo.