[TenTec] Noise Reduction Setting

[Gary Hoffman]

And this is why I said the FIR filter works pretty well.  It takes a darn
good stab at approaching what the really high end filters can do with brute
force....without needing the brute force.  It cannot quite get there of
course, but it works well.  That's what we are all saying I guess.

Ok...I give up.  My intention was hopefully to get Ten Tec to comment.  It
seems rather clear that they choose not to.

We have exchanged ideas among the group in a very civil, interesting, and
informative exchange.  I'm happy with that !  Would that all discussions
could be as good.  But I guess we have extracted all we can for this one, so
I guess I'm going to ease out of it now.

Thanks to all who participated.

73 de Gary, AA2IZ


----- Original Message ----- 
From: "Grant Youngman" <nq5t at tx.rr.com>
To: <geraldj at storm.weather.net>; "'Discussion of Ten-Tec Equipment'"
<tentec at contesting.com>
Sent: Sunday, December 10, 2006 12:03 AM
Subject: Re: [TenTec] Noise Reduction Setting


> > But an FIR or IIR filter can't compare coherent signal to
> > incoherent noise and enhance multiple signals while
> > suppressing the noise between them.
>
> The textbook I referred to is available from Amazon.  You can take it up
> with the author if you don't agree with the mathematical derivation or
> operation of a Wiener filter.  It is written in English, which is my
native
> tongue :-)
>
> I bought it (at the good suggestion of someone, can't recall who, on the
> list), the last time we had this getting-very-old discussion of what might
> or might not make good de-noiseing algorithms.  The book is an excellent
> reference.  And very informative reading, particularly since I have a
> business interest in continuous speech recognition in the presence of (a
lot
> of) noise.
>
> I am NOT an expert in noise reduction but I can read, and generally do not
> misinterpret clear statements.  " .. For additive noise, the Wiener filter
> attenuates each frequency component in proportion to an estimate of the
> signal to noise ratio. ... For additive white noise, the Wiener filter
> response broadly follows the signal spectrum."  Further, ".. [for noise
and
> signal spectra which overlap] it is not possible to completely separate
the
> signal from the noise.  However, the effects of the noise can be reduced
by
> using a Wiener filer that ATTENUATES EACY NOISY SIGNAL FREQUENCY [emphasis
> added] in proportion to an estimate of the signal-to-noise ratio."
>
> I'd be happy to scan and send you Figure 6.5, page 179 of the referenced
> text which describes, graphically,  precisely what I said.  I'd also be
> happy to send the block diagram of the Wiener filter, showing how the
error
> component is used to adapt the coeffiecients of an FIR filter, which is
the
> basis for the discussion on Wiener filters in the referenced text.
>
> At some point, perhaps we should all just go out and beat ourselves with a
> stick :-)
>
> Grant/NQ5T
>
>
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