asterisk users - Dec 2007 - Echo cancellation and DTMF from the Asterisk console?

Hi,

I'd like to try using a good quality microphone and a set of PC speakers 
(in the first instance) to create a powerful speakerphone; if I get that 
working, I'll probably try more elaborate audio equipment.

For this to work, I'll need software acoustic echo cancellation, or the 
caller at the other end will constantly hear his/her voice echoing back.

I gather Asterisk can do very good software echo cancellation, but I can 
see no reference to using it with chan_console (using the Alsa driver). 
Am I overlooking something obvious, or is that really not implemented?

If not, I guess I'll have to try Linphone, as I hear it does pretty good 
acoustic echo cancellation (it uses the code from the Speex library, I 
believe).  that's not an ideal solution, though, as the two would be 
running on the same machine (I'd have to recompile Linphone to use a 
different port for SIP, or else tell Asterisk to do so).

In addition, I've tried using 'dial' from the Asterisk console while
a
call from the console is already established, hoping that this would send 
DTMF signals.  So far those signals haven't been received at the other 
end, while I've had no trouble sending DTMF from a Windows softphone via 
the same Asterisk box.

If all this isn't promising, is there a better way to combine a line out 
socket, a mic in socket and either software or hardware acoustic echo 
cancellation?  I'm not very familiar with the hardware options around for 
Asterisk, but it strikes me that this would be a fairly obvious thing to 
do....  I haven't come across a hardware speakerphone which allows you to 
replace its own speaker and mic with line out and mic in sockets, but if 
there is such a thing, I suppose that connecting it to an FXS socket might 
be a sensible way forward.

Any help much appreciated!

Best wishes,

Nikhil.

Nikhil Nair wrote:
> I gather Asterisk can do very good software echo cancellation, but I can 
> see no reference to using it with chan_console (using the Alsa driver). 
> Am I overlooking something obvious, or is that really not implemented?
>   
IIRC, echo cancellation is fully in zaptel.  If your remote callers will 
be SIP or IAX based, it probably won't be effective.
> In addition, I've tried using 'dial' from the Asterisk console
while a
> call from the console is already established, hoping that this would send 
> DTMF signals.  So far those signals haven't been received at the other 
> end, while I've had no trouble sending DTMF from a Windows softphone
via
> the same Asterisk box.
>   
I don't follow this.  My asterisk (1.4.4) does not have a dial command 
at the console, what are you trying?  I'm
suspecting that if you have something called Dial that it's for 
originating NEW calls rather than sending DTMF down
existing channels.
> If all this isn't promising, is there a better way to combine a line
out
> socket, a mic in socket and either software or hardware acoustic echo 
> cancellation?  I'm not very familiar with the hardware options around
for
> Asterisk, but it strikes me that this would be a fairly obvious thing to 
> do....  I haven't come across a hardware speakerphone which allows you
to
> replace its own speaker and mic with line out and mic in sockets, but if 
> there is such a thing, I suppose that connecting it to an FXS socket might 
> be a sensible way forward.
>   
It seems there would be fairly directional desk microphones you could 
find that you could direct at the user.
Maybe a little cylinder of paper around the end of the mic would help.  
Or maybe the speakers can be turned
down to the point where they aren't picked up by the mic as strongly,  
especially after reducing the mic's level
as far as you can.  I'm thinking with a little cylinder of paper, you 
could drop the mic level pretty far and it would
still pick up the user's voice.  Another idea I've considered is 
wireless headphones... have you considered
chan_mobile with bluetooth wireless headset?  but that probably goes 
against the grain of a speakerphone ;)
> Any help much appreciated!
>
> Best wishes,
>
> Nikhil.
>   
You might consider the oslec echo canceller.  I have no idea where it 
integrates into the call flow, there's potential there,
but I suspect it's zaptel-related too.

Good luck!

Moj
>
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Nikhil Nair wrote:
> In addition, I've tried using 'dial' from the Asterisk console
while a
> call from the console is already established, hoping that this would send 
> DTMF signals.  So far those signals haven't been received at the other 
> end, while I've had no trouble sending DTMF from a Windows softphone
via
> the same Asterisk box.
>   
I see, dial is part of using chan_console, I didn't realize ;)

Moj

In my other response to this topic I mentioned chan_mobile, I could have 
meant chan_bluetooth.

Nikhil Nair wrote:
> Hi,
> 
> I'd like to try using a good quality microphone and a set of PC
speakers
> (in the first instance) to create a powerful speakerphone; if I get that 
> working, I'll probably try more elaborate audio equipment.
> 
Interesting... After playing with - and being very impressed by the 
OSLEC Echo canceller - my business partner and I had an idea about using 
it as a module that could be plugged into ALSA (The Linux Sound 
Architecture) so it could be used with various audio devices. It is just 
a pipe dream at this moment however.

The biggest issue I can see is the delays. OSLEC and the other echo 
cancellers in Zaptel are Line Echo Cancellers and as such deal with with 
very short delays. Acoustic echo Cancellation needs to handle far longer 
delays potentially...

I use the Polycom Communicator C100s desktop speaker/mic on Linux, and 
despite the fact that Polycom integrate "most" of their EC software in
the Windows Driver, it works very well with the OSLEC canceller on the 
line side.

Take a look at the OSLEC package 
(http://www.rowetel.com/ucasterisk/oslec.html) and maybe try and get in 
touch with David Rowe - he is very approachable and very knowledgeable 
on this subject.

HTH

Alan


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