[speex-dev] More Speex (pre-processing) Options

[Tom Harper]

Hi,

So far there does seem to be an improvement in open air mike noise vs.
no denoising, especially in terms of handling feedback- but that is just on
my laptop, which is far quieter than a desktop sound card might be- As far
as removing it completely, I think there were a few posts about that a couple
of months ago that suggested some good approaches- of course, the best
way to solve it is to get a good head phone/directional mic setup :)

Tom

<p><p>At 10:52 AM 11/26/2003, Tongbiao Li wrote:
>This is only remotely related: just out of curiosity, does
>speex_preprocess work very well for you ?
>
>It only works to certain extend for me, and does not seem to completely
>remove noise from sound card.  Even if you unplug the microphone, it
>still could not get rid of the noise.
>
>Any idea how it could be totally eliminated ?
>
>
>Thanks
>
>
>
>-----Original Message-----
>From: Tom Harper [mailto:harper at archila.com]
>Sent: Wednesday, November 26, 2003 10:18 AM
>To: speex-dev at xiph.org
>Subject: Re: [speex-dev] More Speex (pre-processing) Options
>
>Hi,
>
>Thanks, that gave me some ideas.  I have tried calling speex_echo_cancel
>and speex_preprocess separately and jointly, with a number of different
>filter lengths,
>and using the cancelled and non-cancelled data as input to the
>pre-filter,
>with
>and without the residual echo, etc. but there doesn't appear to be valid
>
>data in the
>echo or the cancelled frame any way I try it.
>
>Back to the drawing board (and eagerly awaiting the next release),
>
>Tom
>
>At 05:28 AM 11/26/2003, Tom Grandgent wrote:
> >I don't think the echo canceller works yet.  The best I could
> >get it to do is trash my audio.  If it does work, some sample
> >code demonstrating its use would be really appreciated...
> >
> >Here is what Jean-Marc has said about it in the past:
> >
> > > What should I use for a filter length for speex_echo_state_init()?
> >
> >"Well, it depends on your problem. The filter length represents the
> >maximum delay of the echo. For acoustic echo, that value is generally
> >higher than for line echo. You'll need to experiment, but a value
>around
> >500 (for 8 kHz) might be a good start."
> >
> > > [question about params for echo canceller function]
> >
> >"Actually, ref is the incoming frame (with echo), echo is the outgoing
> >frame (that has only the echo) and out is the echo-cancelled frame. As
> >for Yout, it is an estimation of the residual echo that can be sent to
> >the denoiser so that residual echo can be removed as well. Note that
> >this last feature is still experimental."
> >
> >
> >Tom Harper (harper at archila.com) wrote:
> > >
> > > Hi,
> > >
> > > So I have had a chance to delve deeper into  the new pre-processing
> > > code-  I was also able to get VAD, AGC, Denoising, etc working
>inside
> > of the
> > > current release candidate (1.0.3).   For some reason, the 1.1.2
> > > release didn't properly encode/decode in our system (on windows)
> > > and I haven't had time to determine why.  In any case, all of the
>features
> > > jointly work very well- great job!
> > >
> > > I realize the echo cancellation element may still be in development,
>
> > but I am
> > > having trouble getting that part of the preprocessor to work.  When
> > > I don't pass NULL into the speex_preprocess for the echo parameter,
>things
> > > seem to go haywire- some memory appears to be getting trampled
>somewhere
> > > (this is probably my fault).  Maybe I am misunderstanding the
>purpose
> > of this
> > > parameter?  Except for the first few packets, the preprocessor
> > > appears to be removing all audio- The algorithm I am using passes in
>a
> > recently
> > > decoded frame...  Any ideas?  Do I need to set some settings in
>somewhere
> > > in order for this to work properly?
> > >
> > > Thanks,
> > > Tom
> >
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