Re: [Linphone-developers] Echo Canceler

[Charles Eidsness]

Simon,

Thanks, and thank you for this excellent software. I particularly like 
the mediastremaer framework. It's so simple and straight-forward it 
didn't take me very long to figure out how to implement my own filter.

I had no "show-stopper" issues with a 2 input / 2 output filter but I do 
get some strange errors logged to the terminal that I haven't had time 
to take a look at. These errors don't seem to effect the call at all.

I get a bunch of these:

Debug: sleeping function called from invalid context at mm/slab.c:1989
in_atomic():1, irqs_disabled():1 .... followed by a long call trace

But this is probably just a result of the way I have my kernel / system 
configured.

I get two "Opening soundcard" messages, i.e.:

Message:ms_filter_add_link: OssRead,0 -> EC,1
Message:ms_filter_add_link: EC,1 -> GSMEncoder,0
Message:ms_filter_add_link: GSMEncoder,0 -> RTPSend,0
Message:ms_filter_add_link: RTPRecv,0 -> GSMDecoder,0
Message:ms_filter_add_link: GSMDecoder,0 -> EC,0
Message:ms_filter_add_link: EC,0 -> OssWrite,0
Message:Opening sound card in capture mode with stereo=0,rate=8000,bits=16
Message:dsp blocksize is 512.
Message:Opening sound card in playback mode with stereo=0,rate=8000,bits=16
Message:Opening sound card in playback mode with stereo=0,rate=8000,bits=16

And it doesn't terminate the call very cleanly. I get a bunch of these:

msosswrite.c:148- assertionw->sndcard!=NULLfailed
msfilter.c:414- assertionf->finputs==0failed
msfilter.c:415- assertionf->foutputs==0failed
msfilter.c:414- assertionf->finputs==0failed
msfilter.c:414- assertionf->finputs==0failed
msfilter.c:415- assertionf->foutputs==0failed

As mentioned in my previous email I'm using a fairly unique system. I'm 
running on an embedded MIPS processor using uclibc and using an ALSA 
driver I wrote myself so these errors may not appear on a "normal" 
system, or there may be different errors.

If you add a checkbox for this echo canceler make sure you mention it's 
experimental. :)

I think the algorithm itself could still use some tweaking too. It will 
behave in a different manner depending on the level of background noise 
and so far I've only been testing it with a fixed level. I'll try to 
improve it as I get more time but if there's anyone out there that is 
interested in signal processing and wants to take a look at it that 
would be really cool.

Cheers,
Charles

Simon MORLAT wrote:
> Hello,
>
> I've just had a look on your excellent work, thank you very much.
> I saw that you implemented a 2-input 2-output MSFilter to achieve this, 
> this is actually exactly the right way... but I didn't think that the 
> mediastreamer was able to nearly correctly handle those kind of complex 
> graphs... Actually the scheduling algorithm I've implemented was first 
> designed to run simple linear graphs. You haven't experienced strange 
> things about that ?
> Anyway as it works I will integrate it into linphone and add checkbutton 
> to enable/disable it. It may take some time, because the goal for now is 
> to stabilize the 1.0.0 release first.
>
> Simon
>
>
> Charles Eidsness wrote:
>
> > Hi All,
> >
> > I've been working on an acoustic echo canceler for Linphone. I have 
> > something that kind-of works for me and thought I'd post it in case 
> > there's someone else out there interested. I think it just needs a 
> > little more tuning, I hope to have it functional someday.
> >
> > I've been using Linphone 0.12.1, and am using uClibc on an embedded 
> > MIPS processor so there's a chance it may not work on another 
> > platform. I've been trying to keep everything as fixed-point math 
> > since there's no FPU on my processor but I did implement a couple 
> > filters as floating point. (I'm using soft-float from gcc compiler) 
> > Also, I borrowed liberally from the mark2 echo canceler which is part 
> > of the Zaptel package for Asterisk so you can look at it as well if 
> > you're super-keen.
> >
> > I split my changes / additions into three patches to make them easier 
> > to take a quick look at:
> >
> > members.rogers.com/charles.eidsness/linphone.0.12.1-ec.source.patch
> > -- adds ec.c and ec.h to the mediastreamer
> >
> > members.rogers.com/charles.eidsness/linphone.0.12.1-ec.msEC.patch
> > -- adds msEC.c, msEC.h and test_ec to the mediastreamer
> >
> > members.rogers.com/charles.eidsness/linphone.0.12.1-ec.setup.patch
> > -- edits the mediastreamers Makefile.am, audiostream.c and 
> > mediastream.h to add a echo canceler filter block in the audio stream
> >
> > members.rogers.com/charles.eidsness/linphone.0.12.1-ec.patch
> > -- all three patches in one file
> >
> > Cheers,
> > Charles
> >
> >
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