[Speex-dev] Backup Echo Suppression

[Tom Grandgent]

Jean-Marc,

I think I can speak for most everyone here when I say we appreciate *very 
much* your code beyond the codec that helps people who use Speex in real 
applications.  How far you want to take that code is up to you, of 
course.  (And contributors, to a degree.)

I don't think any reasonable person is expecting your code to solve 
everything.  But when people are running up against very difficult 
problems like these, those kinds of comments are really hurtful.  I know 
I've spent *many* hours trying to make echo cancellation and suppression 
work in my own application, and I've tested various hardware devices that 
claimed they could do it, all with very little to show for it.  (I still 
haven't had a chance to try the latest Speex echo canceller yet.  I 
expect some major reworking of my audio system will be needed before I 
can even think about achieving the necessary synchronization.)

Maybe better documentation of the issues surrounding echo cancellation 
and the exact requirements of your code could go a long way towards 
answering these questions in a productive way.  Some sort of FAQ or wiki 
page specific to the Speex echo canceller, perhaps.  Then, when these 
things come up, you can point people there and say "this has all 
information known to date".  Or maybe the manual is the right place.

Anyway, out of all the challenges in constructing a VoIP system, it seems 
echo cancellation is easily the most difficult.  But it's also extremely 
valuable functionality.  So these issues will just keep coming up.

Tom

"Coffey, Michael" <mcoffey at avistar.com> wrote:
> 
> Millions of ordinary people have systems that do not meet your stringent specifications.
> 
> It does not matter what OS you or I use. It's the customers for whom this work is done.
> 
> -----Original Message-----
> From: Jean-Marc Valin [mailto:Jean-Marc.Valin at USherbrooke.ca] 
> Sent: Monday, July 02, 2007 6:35 PM
> To: Coffey, Michael
> Cc: speex-dev at xiph.org
> Subject: RE: [Speex-dev] Backup Echo Suppression
> 
> Selon "Coffey, Michael" <mcoffey at avistar.com>:
> > Believe me; I've "played with" priorities and buffering.
> 
> Then either you haven't played well enough or you're using a braindead OS.
> 
> > Did you just say you have no idea how the Speex residual echo suppressor
> > works? If that is the case, can you tell me where I could get some
> > information about it?
> 
> What I'm saying is that I've no idea how the residual echo suppressor reacts
> when it's used in a way it wasn't designed for (i.e. working around broken
> audio capture/playback).
> 
>    Jean-Marc
> 
> > -----Original Message-----
> > From: Jean-Marc Valin [mailto:jean-marc.valin at usherbrooke.ca]
> > Sent: Friday, June 29, 2007 7:38 PM
> > To: Coffey, Michael
> > Cc: speex-dev at xiph.org
> > Subject: Re: [Speex-dev] Backup Echo Suppression
> >
> > Coffey, Michael a écrit :
> > > I realize that the preprocessor echo suppression is not designed
> > > specifically to counter the effects of data loss. On the other hand, as
> > > much as I might like to, I do not have the option to "fix that problem
> > > for real." The sad truth is that some end users have systems that may
> > > drop samples, or do other unfathomable things, no matter what I do. I
> > > can not rewrite their drivers, firmware, or operating system. My job is
> > > to do the best I can in a difficult situation.
> >
> > Actually, there's still a lot you can do. You can reduce the amount of
> > sample drops by playing with the priority and the amount of buffering
> > you do. Also, there are sometimes ways to make sure that the drops don't
> > change rec/play synchronisation (the key is the sync, not the lost
> > samples). As for how the residual echo suppression works, I've no idea,
> > you need to try.
> >
> > > I initially assumed that the echo suppressor is similar to other echo
> > > suppressors (also called "nonlinear processors" or "loss controls").
> > > Those suppressors use cruder algorithms that exhibit artifacts but that
> > > may not depend on the fine time structure of the audio signals. Is this
> > > not true of the preprocessor echo suppressor?
> >
> > Not sure what other echo suppressors do. Some are actually designed to
> > act alone while others (like the Speex one) are designed only to
> > suppress the echo that was left by a first echo canceller.
> >
> > 	Jean-Marc
> >
> > > -mjc
> > >
> > > -----Original Message-----
> > > From: Jean-Marc Valin [mailto:jean-marc.valin at usherbrooke.ca]
> > > Sent: Tuesday, June 26, 2007 8:49 PM
> > > To: Coffey, Michael
> > > Cc: speex-dev at xiph.org
> > > Subject: Re: [Speex-dev] Residual Echo Suppression by the Preprocessor
> > >
> > > The residual echo suppression is supposed to be working decently well
> > > now. However, it's not designed to counter the effects of samples being
> > > dropped off the soundcard. You'll just need to fix that problem for
> > > real.
> > >
> > > 	Jean-Marc
> > >
> > >
> > >
> >
> >
> 
> 
> 
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