[Speex-dev] voice activity detection

[Joachim Boomberschloss]

Thanks Tom and Steve. Your replies make me quite
happy. It is strange that this information is not
available anywhere other than this list!

Joe ;)

--- Tom Grandgent <tgrand at canvaslink.com> wrote:

> Yes, you can use it independently by using
> speex_preprocess().  
> This function can do noise removal, AGC, and VAD. 
> I've been 
> using it to do all three and it usually works very
> well.  There 
> can be a train going by outside, producing lots of
> sound that 
> makes it through the noise filter, and yet the VAD
> knows it's 
> not speech.
> 
> However, sometimes the VAD seems to get into a bad
> state and 
> will either always indicate speech (even when the
> input is 
> very nearly silent) or rarely indicate it such that
> the person 
> has to shout to be heard.  When this happens, it
> never recovers, 
> and I have to destroy and recreate the state to fix
> it.  I don't 
> know what could be wrong... it probably works fine
> for everyone 
> else...
> 
> Also, be aware that there are probabilities that can
> be tweaked 
> to alter the sensitivity of the VAD, as described in
> this post 
> to the list awhile ago:
> 
> At 06:37 AM 5/18/2004, Steve Kann wrote:
> >I don't seem to get that;  I suppose you've already
> changed the thresholds 
> >to make things more sensitive though:
> >
> >This is what I have now in iaxclient; the first
> number is the "initial" 
> >probability to go from not speech -> speech.  The
> second is to go from 
> >speech -> not speech.  [the difference implements
> hysteresis].
> >
> >/*      if (st->speech_prob> .35 ||
> (st->last_speech < 20 && 
> >st->speech_prob>.1)) */
> >      if (st->speech_prob> .30 || (st->last_speech
> < 20 && 
> > st->speech_prob>.07))
> 
> Might be helpful for you.
> 
> Tom
> 
> Joachim Boomberschloss <boomberschloss at yahoo.com>
> wrote:
> > 
> > Hello,
> > 
> > I am wondering whether Speex's voice activity
> > detection mechanism can be used independently of
> > encoding and decoding speech, and how reliable it
> is
> > in general. I need this kind of functionality for
> a
> > project I am working on, and I was wondering if
> Speex
> > provides it in a ready-to-use fashion, or if it
> > requires modification of the source code. If so, I
> > would be glad to consider doing this work for the
> > benefit of others with some guidance (depending on
> > complexity and usefulness).
> > 
> > Thanks,
> > 
> > Joe.
> 
> 



		
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