From: pmc@world.std.com (Patrick M Chase)
Subject: Re: Explaination of Dolby and tapes
Organization: The World Public Access UNIX, Brookline, MA
Date: Tue, 25 Aug 1992 17:19:00 GMT

In article <1992Aug25.072346.22910@uvaarpa.Virginia.EDU> Jeff.Burchell@f305.n109.z1.fidonet.org writes:
>
>Dolby is basicly playing with an equalizer, but not perfectly. I can create my
>own dolby with my equalizer if I make a tape that only I play... Then I can
>compensate nicely and make good clean tapes. Otherwise I prefer to listen to a
>non-dolby tape (In fact Id rather cut a dolby tape with a good EQ than with a
>dolby button, I find I make it suit my tastes)

You can't imitate Dolby compression with a EQ. The EQ will diminish selected
frequencies across the board. That's not how Dolby works. If Dolby technology
was simple filtering like that then why would anybody use it? Why would it be
industry standard?

As you said, Dolby B expands high freqs onto the tape during the recording
process. Upon playback the sound is correspondingly compressed. The upshot is 
that the noise level inherent in the tape remains the same during recording
(the music is expanded and then put on the tape) and that same noise (hiss) is
therefore compressed upon playback.

So music is played back the same as the source recording (all things
considered) and the tape hiss is compressed or mitigated at the same time.

Now that's the way I understand Dolby B, and how it's stated (albeit a bit
more technical) in the Dolby Labs press sheets I've read. If I've got it right,
you certainly cannot do that with your EQ.

Other than that, I agree with you as far as *using* it goes. I've heard some
pretty miserable Dolby decoding and prefer to EQ the highs down a bit rather
than encode the music. I don't advocate EQing recordings - especially when
they'll be passed onto the next guy (and dozens after that). I prefer that all
the freqs of the source recording are represented in the copy - regardless of
how people upstream feel about it. You can always do post-processing on it.

I feel the same way about what some people call "image-enhancement" which is
often more like "image-destruction". Quantizing from 24 bit planes down to 8
and using lossy compression and all that - all to make an image look a tad
better on a *specific* display. The rest of the world has to live with these
alterations.

Someone, way back when, when we had a major EQ discussion also discussed the
effect of EQing the root notes out and therefore leaving "orphan" overtones
that leave the recording unbalanced.

Hmmmm..... I'm getting off topic a bit here.... better cut my losses.
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