[Asterisk-Users] Tweaking AGGRESSIVE_SUPPRESSOR

[Steve Underwood]

Dennis Webb wrote:

> This seems to be how AGGRESSIVE_SUPPRESSOR works.  To make sure you 
> don't get echo, it does what a speakerphone does, mute the other party 
> if it hears audio from your end.  There is a setting in mec2_const.h 
> for AGGRESSIVE_HCNTR=160 that says in the comments 20ms, I'm assuming 
> this is to tell how long to suppress the other party.  There is 
> nothing on this that I have found anywhere and since we are live, I 
> can't change until later to see how it works.
>
> We have Polycom SIPS for users, and it doesn't matter what the other 
> party is.  It seems from another thread, that the problem midcall is 
> that the electrical properties of the line change midcall causing the 
> echo to return.  Without AGGRESSIVE_SUPPRESSOR defined the first 
> minute or so is fine, then a click happens and the echo begins.  The 
> phones also seem to go extra sensitive then.  You can then hear even 
> keyboard clicks from typing where you don't normally.  I've wondered 
> if it's the zaptel cards or poor electricity at my place to the 
> asterisk server.  I have put in a SmartUPS 1500 to try to condition 
> electricity there just to make sure.

The problem mid call is due to a bug in the wctdm driver. It slips 
frames. When that happens, the echo canceller's training is completely 
wrong, and the echo comes back. It might even be rather worse than with 
no canceller at all. This is the same problem which prevents the TDM 
cards working reliably with FAX machines. I don't know if action is 
being taken to fix this.

> As far as echo and PRI, thanks for making me cry since I just knew 
> that would solve it.

Well, it better than buying more stuff, and being disappointed. :-)

Regards,
Steve