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From: rcd@opus.UUCP (Dick Dunn)
Newsgroups: net.audio
Subject: Copying dolby-ed cassettes (answer)
Message-ID: <635@opus.UUCP>
Date: Sat, 21-Jul-84 04:09:11 EDT
Article-I.D.: opus.635
Posted: Sat Jul 21 04:09:11 1984
Date-Received: Mon, 23-Jul-84 01:34:53 EDT
Organization: NBI, Boulder
Lines: 22

A while back, I posted a question asking whether it would be OK to copy
cassettes recorded with Dolby (TM) noise reduction by turning off the NR
switch on both playback and record decks, thus saving two passes thru the
NR circuitry.

The answer, in general, is NO.  [I should have been able to figure it out
for myself, but sloppy thinking prevailed.  Thanks for rabbit!ark and a
couple of others (whose names I lost) for pointing out the problem.]

The difficulty is that the noise-reduction is not a linear effect with
respect to signal level - it boosts low-level high-frequency signals before
recording and correspondingly attenuates after playback, but it doesn't
alter high-level signals as much.  Thus the process is sensitive to
recording level.  This means that you'd have to set the record level on the
recording deck to match the level at which the playback tape was recorded,
which would be tricky at best.  It's probably better to make the two passes
through the NR circuitry than to risk the problem of Dolby mistracking.

Now, if the tapes were digital, none of this fuss would be necessary.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
	...A friend of the devil is a friend of mine.