[speex-dev] speex_denoise on non-microphone noise (static ?)

[Tom Grandgent]

I'm not sure you'd have much success in trying to make a generic profile 
to fit the "typical noisy PC" since PC configurations vary so much.  
Consider an integrated AC97 codec vs. the mic input on an SB Live!/Audigy 
Live!Drive, or whether or not the input from the CD-ROM audio is muted, 
or what noisy devices might be situated near the mic.  It's nice 
to be able to get rid of environmental noise too.  In my experience this 
has been much more troublesome than internal/interference noise.

And chances are, you have to use some kind of wizard to get the user to 
set their volume levels correctly and speak properly into (and test) the 
microphone, so it shouldn't be too much harder on the user to have the 
profile get built as part of that...

Tom

Tongbiao Li (tli at viack.com) wrote:
> 
> That's might be speex_denoise() is trying to do already, based on the
> fact that if noise is present in speech signal, the former gets
> suppressed to a certain extend.  Also, I noticed after suppression, the
> short, noisy attack - speex_denoise() have to be doing some kind of
> profiling.
> 
> I've looked at a few offline denoise() solutions.  They all involve
> profile building.
> 
> A real-time solution is needed for our particular domain.  Somehow,
> during speech, we want to build the *profile*, and subtract it from the
> subsequent signals.  My question is: anyone have any idea on the profile
> of the *profiles", or the dynamically building of it, assuming just the
> interaction from other internal organs of the PC, and no fans etc.
> around?
> 
> Meanwhile, I guess the initial solution is force the customers run some
> kind of wizard, before the running stage of our software, while
> (secretly) building up the profile, hoping they do not adjust their gain
> level etc later.  Any comments (experience) on this, from anyone ?
> 
> 
> -----Original Message-----
> From: Tom Grandgent [mailto:tgrand at canvaslink.com] 
> Sent: Thursday, September 18, 2003 11:25 AM
> To: speex-dev at xiph.org
> Subject: Re: [speex-dev] speex_denoise on non-microphone noise (static
> ?)
> 
> Hi,
> 
> I'm not sure how speex_denoise() works, but my solution to this problem 
> is fairly straightforward and works well in practice (in a simple VoIP 
> program.)  Note that I am also an amateur and am making up some 
> terminology here... but I've tested my approach on several noisy 
> environments with low-quality mics and it does work well.
> 
> Problem: There's usually annoying noise present in a recorded signal, 
> which can be attributed to interference from the PC and background noise
> 
> in the user's environment (fan noise is common.)
> 
> Assumptions: The noise is regular with respect to time - that is, it's 
> steady and ongoing.  It tends not to change significantly in frequency 
> or amplitude over a long period of time.
> 
> Solution: Subtract it from the signal.  In order to do this, there are
> two 
> steps required: 1) Build an average profile of the noise.  This is done 
> infrequently and [currently] triggered by the user.  2) Subtract the 
> profile from the signal.  This is done before encoding the signal with 
> Speex.
> 
> 1) Building the profile: I build an "average profile" of the noise in
> the 
> frequency domain.  So the user is prompted to be quiet for a few
> seconds, 
> the noise is recorded, and it's run through the FFT.  The signal is 
> averaged (in the frequency domain) over those few seconds to get a
> "general 
> idea" of the noise characteristics.
> 
> 2) Removing the noise: Before encoding some recorded sound with Speex, I
> 
> run the sound through the FFT.  Then it's a simple matter to loop over
> the 
> frequency spectrum and subtract the noise profile.  At this point it's 
> also easy to do simple filtering, so I do a high-pass filter around
> 200Hz 
> or so to get rid of unwanted bass.  Then, I do the inverse FFT to get
> the 
> sound back into the time domain, and I encode it with Speex.  The noise 
> is *greatly* reduced.  The difference can really be dramatic.
> 
> Drawbacks: Not all noise is regular over time, and this approach is a 
> manual, non-adaptive process (for now anyway...)  One person I talk to 
> has a monitor which causes annoying noise only when the screen is mostly
> 
> white.  So sometimes I end up asking them to rebuild the profile.
> 
> Well, I'm not sure if this is helpful or not, but it works for me.. :)
> 
> Tom
> 
> 
> Tongbiao Li (tli at viack.com) wrote:
> > 
> > The problem started with speech detection.  Speech sections are
> detected
> > well.   However, once in a while non-speech sections are also marked
> as
> > speech.  The root was finally traced down to microphone static noise.
> > 
> > Then I pulled the microphone out. Our system still records noise.  To
> > isolate the problem, I wrote a small app just to open the device and
> > record raw samples, calls speex_denoise() and outputs both sample
> sets.
> > The noise is still there, with level fluctuating with gain level,
> unless
> > "All mute" is chosen.  
> > 
> > In the case when NO microphone is plugged in, speex_denoise() smoothes
> > the signal and produces smoother (and even amplifies the signal)
> speech
> > like signals.  It seems that speex_denoise( ) is very sensitive to
> > static noise.
> > 
> > For regular speech COMBINED with microphone static (or more precisely,
> > the static detected at the microphone plug, or noise from inside the
> PC
> > ... someone help me out here), the noise samples do get suppressed
> > compared to speech samples. 
> > 
> > One observation: many noise sequences seem to have a signature of
> sharp
> > spikes.
> > 
> > Anyone have a solution of supressing this type of static?
> > 
> > Thank you.
> 
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