Re: [ecasound] Noise reduction

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Subject: Re: [ecasound] Noise reduction
From: Evan Langlois (goth_74@yahoo.com)
Date: Tue Dec 28 1999 - 00:37:41 EET


Well, I don't know much about ecasound, but I do know
a little bit about noice reduction. There are two
methods commonly used to reduce noise in analog tapes.

The first, which doesn't apply much here, is to
increase the amount of high frequency as the tape is
recorded, then when playing it back, you reduce the
high frequencies - which also reduces the tape hiss in
the upper frequency range. You record it with a
louder upper frequency range so that when you reduce
it at playback, it will sound normal. This is the
Dolby B setting on your tape deck.

The other methods, including dbx and Dolby C use an
expansion noise/gate combination, sometimes in
addition to the trick above (Dolby C) or by first
splitting the audio spectrum into parts that
compress/expand seperately for better over-all dynamic
range (dbx). This produces an overall better dynamic
range for the tape, as well as removing most of the
noise, but you'll never find it in commercial music
publications.

You can get real close to CD quality by using HXPRO
recording bias with Dolby C noise reduction, but you
need Dolby C to play it back. Both of the above
really need special recording to be really effective
without coloring your sound though.

Now, as to your problem. First make sure your
playback used the same noise reduction as the original
recording, probably Dolby B or nothing at all, and use
good cables and a quality sound card that doesn't add
additional noise. Then you can try running it through
an expansion process. By carefully setting up the
expander, you should be able to drop the noise (and
unfortuneatly any soft parts to your music) further
down in the dB range - enough to where a noice gate
can shut it off completely, and also get some more
dynamic range out of your recording. This is really
great between tracks where you need it the most! Your
noise will just go away!

If you still have noise, lighten it up a bit with an
equalizer with a tight frequency range. You want
almost a single frequency - I believe its right around
12Khz (could be wrong on that one).

You can kill a little extra noise (and some of your
signal) if you have a harmonic exciter (don't know if
ecasound does this one). Basically, its an attack
sensitive circuit that increases high frequency
information in a narrow band (usually around 16Khz,
but some are tunable) in proportion to attack. This
can really bring cymbal crashes and such out of a mix.
 Most very high frequency information tends to be
pretty dynamic, while noise is almost constant, so the
exciter can bring it up a bit for you - and you will
generally turn down your noise with the EQ AFTER you
bring out the information you want with the exciter.
You will color your over-all sound a bit doing this,
but if your careful, you can probably get favorable
results.

You may wanna check FFT graphs of your sound before
and after your complete noise reduction to make sure
your end-result is EQed close to the original - and
you can adjust it with an equalizer and re-tune
everything if you need to (possibly turn down the
exciter center band, or whatever other adjustments you
need). If you do straight EQing to get rid of the
hiss frequencies, try it both before and after the
expansion process - depending on how you adjust the
expander ratios and centers, and if you can expand the
high frequencies separate from the rest of the music,
you can get better results EQing before instead of
after, or both. Likewise with the exciter.

Play around with it and see what sort of results you
get. The best will very depending on your tape
quality, recording equipment, how sensitive your ears
are to artificial expansion effects, and what sort of
music is on the tape.

Good Luck
-- Evan Langlois

--- Ben Crowder <crowderb@netbrick.com> wrote:
> Hello,
>
> First I must say that I've been very impressed with
> ecasound so far. I
> love the clean design, and it just feels wonderful!
> ;) Now on to my
> question: I've recorded some music from cassette
> tape into wave files. As
> those of you who have done this know, there is
> background noise that is
> quite noticeable. Is there any way to reduce or
> eliminate this in
> ecasound? I've tried some of the filters (I don't
> know much about DSP
> which is hindering my progress), but I haven't yet
> been able to get
> results. Is this even possible?
>
> Thanks,
> Ben
>
> -----------
> "The ultimate measure of a man is not where he
> stands in moments of comfort
> and convenience, but where he stands at times of
> challenge and controversy."
> -- Martin Luther King, Jr.
>
>
>

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