rcd@opus.UUCP (Dick Dunn) (07/21/84)
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.berry@zinfandel.UUCP (Berry Kercheval) (07/24/84)
With respect to copying a Dolby*-encoded tapes with the decoding off, Mr. Dunn indeed has the correct answer: Don't! I once asked our VP of Engineering (now company president) who in a former life was Engineering manager at Dolby Labs in San Francisco. He gave me basically the same answer, adding that the Dolby encoding is very level-sensistive, and unless your deck calibrations match very closely, ensuring that a signal of n nano-webers/meter squared on one tape winds up at exactly the same n on the other, it will get all screwed up. Berry Kercheval Zehntel Inc. (ihnp4!zehntel!zinfandel!berry) (415)932-6900 --------------------- *Dolby and the Double-D symbol are registered trademarks of Dolby Labs, Inc.
bytebug@pertec.UUCP (07/25/84)
> Now, if the tapes were digital, none of this fuss would be necessary. > -- > Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 Yes, and how long would the recording industry last!?! Has there been any discussion on the net about what could be done to keep people from pirating digital cassettes? A digital version of "Copy Guard"? :-)
spoo@utcsrgv.UUCP (Suk Lee) (07/29/84)
What is the industry doing to prevent
pirating? Well, you may have noticed
that NO home CD player has digital
outputs--only analog. Of course, it's
pretty easy to dig around inside and
extract it yourself....
--
From the pooped paws of:
Suk Lee
..!{decvax,linus,allegra,ihnp4}!utcsrgv!spoo