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Conference cookie::notes$archive:cd_v1

Title:Welcome to the CD Notes Conference
Notice:Welcome to COOKIE
Moderator:COOKIE::ROLLOW
Created:Mon Feb 17 1986
Last Modified:Fri Mar 03 1989
Last Successful Update:Fri Jun 06 1997
Number of topics:1517
Total number of notes:13349

94.0. "Digitized Hiss" by ASGNQH::SMITH () Tue Mar 19 1985 02:51

		I recently purchased a David Bowie Greatest Hits
		compact disc. It said on the cover that it was
		DIGITALLY REMASTERED. When the signal level was
		low enough, I could hear what I considered to be
		an objectional amount of hiss. It was not there
		between cuts, as the hiss faded out with the
		music. Can't any hiss present in the original be
		eliminated when it is, as they said on the cover,
		Digitally Remastered, or is hiss on the source
		tape impossible to remove? I was under the im-
		pression that hiss removal was one of the bene-
		fits of Digital Remastering.
T.RTitleUserPersonal
Name		DateLines
94.1MANANA::DICKSONTue Mar 19 1985 09:1923
Nope.  The hiss is inherent in the original master (analog) tape.
All digital remastering onto a CD gets you is:

1)  No surface noise
2)  No additional distortion from the limitations in
    groove technology
3)  No degradation after many playings
4)  Being available on the new "in" medium.

For important recordings, benefits 1-3 are considered worthwhile.
They are even reissuing analog recordings of Wagnerian operas on
CD, because of the importance of the program material.  The Boehm
series of the Ring was recorded in 1966/67.  Sure there is hiss,
but there is also Birgitt Nilsson.  You could make new recordings
(and they do record operas in digital these days), but you wouldn't
get Nilsson.

So if David Bowie's Greatest Hits are worth preserving, or if you
think the groovy version has limitations, the CD is worthwhile.

A Digitally Remastered onto CD recording from an analog real master
WILL sound better than an LP made from the same tape, but not
tremendously better.  And the hiss for sure will still be there.
94.2PICA::HIDERTue Mar 19 1985 10:1616
  I think there is a subtle difference between taking an analogue master
  tape and making a digital master from it and taking the original
  session tapes and remixing it to make a new *digital* master.

  In the first case your digital master will inherit all the noise and
  compression of the original analogue master.  In the second case you
  will still get the tape hiss, but you should get better dynamic range
  as compression has not been applied.

  I would hope that if a CD says "digitaly remastered" then it means the
  latter has been done.  Of course, in order to get you to buy it the
  words "digital" and "mastered" take on new meaning.  Beware the small
  print!

    ..Paul
94.3ORAN::ORANTue Mar 19 1985 14:1124
This kind of confusion is what the new XXX rating system is supposed to
clear up. Philips uses it on all their disks, and I've noticed a bunch
of other high-class labels doing the same. But RCA, CBS,etc....not yet
(maybe they're too embarassed). I think the system was summarized in
a prior note, but I'll repeat it here

1. Each letter X is either an A=Analog or a D=Digital

2. The first letter tells you what the unmixed/unedited master medium
   was.

3. The second letter tells you how the editing was done.

4. The third tells you what the consumer medium is. CDs are always D,
   records and cassettes are always A.

Example: DDD = Digital recording, Digital mix/master, Digital playback.
         DAD = Digital recording, Analogue mix, Digital playback
         DAA =   "       "            "     " , Analog  playback

Look for this stuff on your CDs !

/Dave Oran
94.4CRVAX1::KAPLOWTue Mar 19 1985 18:515
	This same note was on the audio notes file, and I responded to 
it there, before seing it here. I said most of the points in .1, but it 
can be sumarized with one word that should be familiar to us all:

				GIGO!
94.5TINCUP::PETRARCAFri Aug 30 1985 16:3416
Admittedly I am not a world class bit diddler - or even a reasonable hacker -
but it seems to me that once a master was digitized for conversion to CD that
a repetitive pattern of the master hiss could be defined through pattern 
recognition and synced with the noise pattern on the exsisting disk and then 
subtracted from each digital word before being put on the CD format. Any
comments from you software folks? How did Mobile Fidelity get such good
results on Sonny Rollins' "Way Out West"?

Also - comments as to whether you would like to see the hiss faded out between
cuts or left at t constant level are solicited.

I would like to see the level remain constant - seems less irritating than the
on/off syndrome - once you have accepted it the brain gets slightly numb. For
reference: two of the CDs which come to mind are "THE DOORS" complete with all
their inherent distortion but a great disk; and selections from "HEAR THE LIGHT
II" by Eric Clapton and Stan Getz.
94.6BAGELS::ROSENBAUMSun Sep 01 1985 19:136
re .-1

	Presumably, the problem with "subtracting hiss," is that it is
*not* repetitive; rather, it is random and unpredictable.
94.7SCOTTY::CREASERFri Oct 25 1985 10:439
It is random in the local domain, however most musical source is not and
the musical pattern can be identified, subtracted from the total and yield
"hiss only image" which can then be subtracted from the total! This has
been used to inhance certain noisy scanned images. Unfortunately I can't
speak to the details of this process, but I would be surprized if other
noters where equally limited. I'm not sure why it necessary to have each
of these steps (O-M=N and O-N=M, where O is orginal signal, M is derived
music, and N is noise) rather than simply accepting M when first derived.
Perhaps there are intermediate steps I'm unaware of.