[Asterisk-Users] Are my expectations too high?

[Andrew Kohlsmith]

On Tuesday 23 May 2006 08:35, Dr. Michael J. Chudobiak wrote:
> Get an FXO card with hardware echo cancellation. I use the Sangoma
> A20002D (four FXO ports with echo cancellation). It definitely costs
> more, but the hardware echo cancellation makes a huge difference in call
> quality! Software echo cancellation doesn't really work...

While I agree that the Sangoma cards are good, your statement that "software 
echo cancellation doesn't really work" is ... incorrect.

Software echo cancel works very well if it's done correctly, if your audio 
levels are where the canceller's "sweet spot" is, and the tail is not longer 
than the longest tail that the canceller's designed to work with.  Most 
people don't attempt to set their stuff up correctly and they achieve poor 
results and blame it on the software.

Asterisk's software echo canceller isn't the best, this is true, but it is 
open source and has been improved upon by several different people. It is 
dark, dark juju though, so the number of people who have the skill to hack on 
it is rather limited.

Regarding echo tail: Asterisk's default software echo cancellation is only 
32ms at maximum.  You can blow this number up to 128ms (where the hardware 
echo cancellers sit at), but it costs more in CPU time and memory, and I 
think that Digium left it at 32ms as a compromise.  I'm not sure.

> I don't know what to suggest about your hiss problem though.

My guess is that he has his audio jacked up so high the thing hisses, or he's 
got a very noisy (EMI/RFI) environment.

-A.