Conference cookie::notes$archive:cd_v1

No, CD's can not take a lot of abuse.  They are quite delicate, and
are especially sensitive if the scratch is circumferential rather
than radial.  The label side is more fragile than the shiny side.

That's interesting.  I can understand that circumferential scratches would
be worse than a radial one.  Why is the label side more fragile?  I had
assumed that all the information was recorded on only one side - the non-
label side.  I think I need to read up on this a little more.  Thanks.

Dick

True, all of the information is read from the non-label side (that is, the 
digital information read by the laser. Obviously you read the label from the 
label side). Consequently, the clear plastic coating is thicker on that side, 
to protect the actual medium. A deep scratch in the label side could damage 
the actual foil containing the data.

The plastic is thick on the shiny side, but very thin on the label
side.  So it is actually less well protected on top.

LV aside:

Many years of LP handling has trained me to be very careful handling my
collection of 12" LV discs.  They all look like new.

However, my experience with rental discs seems to indicate that careful handling
of LV discs is not that important.  Many of the rentals I gotten look like
they've been used for frisbee practice on an asphalt parking lot - scratches,
fingerprints, dirt, ...  The only time my player had any problem with one
of these grungy discs was when the disc was cracked.  Even then, after I
skipped past the crack (about 1/4" into the program area), the rest of the
disc played fine.

I wonder if this experience with analog LV discs hold for the new LV discs
with digital sound?

-- Ward

I don't know if this helps any but several years ago when LV was introduced,
Pioneer held a conference in Boston for audio/video dealers to explain the
new laser formats and performed the following demonstration:

Everyone was seated around a large horse shoe table arangement and the dinner
served was roast beef.  At the end of the meal, people were told not to wipe
their hands on their napkins but instead to examine a disc.
                                                                   
After everyone had looked at it, any excess food was wiped off the disc with a
cloth and the resulting disc was played.  In all cases but one the picture/sound
quality was excellent and got a loud round of applause. 

Steve

Even better is the demo disc Pioneer made available in it's first year of
shipping LV players...

In this disc "Mr Wizard" explains how a LaserDisc works. One of his
experiments is to smear a ice cream cone across a disc, wipe it off and
play it with zero problems.

Neat disc...


Ray

Several months ago there was an article in the Boston Globe on durability
of discs.  The author performed the ultimate test.  He gave it to is three
year old to play with for a day.  The kid dragged it and threw it around
all day.  At the end of the day, the author wiped of the peanut butter and
jam with a damp cloth and it played perfectly.  I have not seen any reason
to use special cleaners.  As previous responses have said, the key not to
wipe in a circular manner where a whole stream of bits could be damaged.
The other way that you can do real damage to a disc is to store it in
a hot car.  It will warp.  I suspect that a badly warped disc could do serious
damage to the laser.

Jack

Along this line, you might be interested in the following.

Some months ago I bought a disk back east (I'm in Colorado). When I got home
and played it I discovered that it had a defect that dropped out about 3
minutes of play. I didn't think that it was practical to send it back to the
dealer at that point, so I decided to experiment.

Looking at the disk closely I could see a defect in the surface of the plastic
that was about a millimeter across. I tried cleaning the surface, but the
defect was embeded in the plastic and wouldn't come out. Not having much to
lose, I took a Q-tip and some Dupont rubbing compound (the type you use to
get scratches out of automobile finishes) and rubbed out most of the defect.

The disk now plays all right, however, there is still a "pop" or two in the
repaired area. I was probably very lucky and don't recommend this procedure;
under a magnifying glass you can easily see scratches left behind by my
rubbing, so I could easily have damage the disk further rather than repaired
it. Still it's something to try if all else fails.

By the way, while I agree that the plastic on the label side is thinner, I
have a hard time figuring out how you might damage the label unless you
attack it with a knife. I would guess that it is thick enough to protect
against casual scratches or fingerprints.

			Regards,
			   George

Re: .9

If your going to try and repair the disc you might want to try the plastic
cleaner and filler kit that Brookstone sells.  It's a two step process.

1) Clean the surface - with the special cleaner

2) Apply the filling compound (white).  You then rub gently to get it to
   go into the scratches, then wipe off the excess.  Depending on how deep the
   scratches are it may take 2-3 applications.  After it dries you can't see
   a scratch even up close.

I've used this stuff on the dust cover on my turn table and was very impressed.
If I remember correctly the kit sells for between 9 and 12 dollars and is
worth every penny.  Since it dries clear it can even be used on smoked plastic
without being noticed.

Steve

LV disks are not digital, but analog.  A smudge would appear as a brief
piece of snow.

CD disks are digital.  Errors do not "average out" like they do in
an entirely analog medium.

(Yeah, I know LV disks are just recorded with ones and zeros, but
it is Pulse Width Modulation, and a simple analog detector turns
the bit stream back into video.  No D/A converters.)

Yes, CDs are digital.  Even though errors don't "average out", most of them
are corrected by an intensive error correction scheme.  Lots of the digital
information on CDs is used just for error correction.  I've read that
the error rate can be as high as one clobbered bit in a thousand with no
problem.  I think it all depends upon how many errors are concentrated in
one area (like if there's a blob in the plastic coating) then the error
correcting scheme can't handle it and you get clicks or skips.

I would think that it would be worth trying to repair a disk.  If the
plastic coating is scratched or has a blob in it, the laser beam is going
to be deflected out of the track.  Repairing this optical coating (the
plastic) so that it looks good will probably keep the laser beam happier
too - although maybe all of this is akin to brain surgery.

Repairing a disk is a little labor intensive, though.  It's probably better
to send it back to the manufacturer and get a new one.

Disks are manufactured in such quantity that statistical methods are used
for quality control.  This means that you have a chance to get a bad one
in proportion to what the company paying for the pressing is willing to spend
on inspection.  When you're in a no-lose situation, it's ok to sit around
and tweek up a disk with a surface blemish, but it's nothing you'd want to
do on a regular basis.
						>>>==>PStJTT

I just read a few days ago that CD's are much more vulnerable on the label
side than one the 'pit' side. In net.audio, someone wrote of scratching
their initials onto the label side with a penknife. He claimed the scratches
were barely visible (you had to hold the disk at just the right angle to
see them) yet he effectively wrecked his CD. Upon closer examination, he
discovered that the scratches had indeed damaged the foil. The protective
layer is much thinner on the label side than on the pit side. Someone else
mentioned reading about some manufacturer boasting of making disks with
thicker, more protective layers. The reader originally scoffed at the claim
as being mere hype, but maybe there really is something to it. It's a
shame to have what is a potentially indestructible medium made vulnerable
to scratches because manufacturers are too cheap to put a decent coating
of plastic on both sides...

I ran into mistracking problems because of surface contamination for the
first time the other day.  The player repeatedly played the same portion
of the selection over and over.  There were a few barely visible smudge
marks on the disc (only visible as dull spots in the reflection off the
surface).  Fortunately, wiping them off solved the problem.  It took me
a few tries with the dust cloth, though, before I got them all and the
mistracking stopped.

--PSW

I have a Toshiba player. I once put black adhesive tape (the sort used for
taping PC board layouts in the good old days) abt 0.1 inch wide on a disk
(radially). No tracking problems.

Re: .17

Unlikely, as that is probably done at the pressing plant, of which they must
be using one of the 9 currently in operation.  (my "Year of the Cat" was
manufactured by Sanyo, Japan)

							-Dave

Well, I got into trouble with surface contamination the other day on a
couple of CDs.  The symptom was severe mistracking; the player basically
wouldn't go beyond a certain point on the disk.  In the first case, it was
a white cat hair that started radially but curled around and was
circumferentially positioned at the end.  Removing the cat hair solved the
problem.  The other one was more mysterious.  I couldn't see anything on
the surface (it all looked mirror-shiny like it's supposed to), but there
was something causing the mistracking.  Rubbing the disk surface radially
pushed whatever it is from place to place on the surface (the mistracking
moved).  After playing around for about 15 minutes, I was able to remove it
completely and the mistracking stopped.

--PSW

	As I ahve told many people many times: Throw away your cats! Or at
least kick them frequently!

	Bob "I Hate Cats" Kaplow

The first disk I bought (2:00 AM Paradise Cafe - Barry Manilow, but not Barry
as you know him - good "piano bar jazz" type music - short review there) got
damaged after about a week: a ding - DUC (Ding of Unknown Cause). Having 
nothing to loose, I started polishing - LIGHTLY - with toothpaste (don't know
if flouride hardens the plastic). First pass left a light filmy look in the
area. COLD water wash - radial dry and back into the player. Better but still
mistracking. Repeat above sequence. Now great - NO INDICATION IN THE SOUND
THAT ANYTHING WAS WRONG. The light scratching is still evident.

Re 115.9: how about trying toothpaste on your disk and reporting back??

Use Q tips with the toothpaste. Sorry

						Bruce

And, as it says on most CD's, be sure to "polish" radially, and not 
concentrically ...

    I don't know if anyone will ever read this (the original note was
    written so long ago now), but I have a question about cleaning CDs
    by rubbing them with a soft cloth--wouldn't that load them with
    a static charge (that could easily attract more particles from the
    air) and possibly cause the laser to mistrack? Please let me clarify
    this question: I know that particles sticking to the disc could
    cause mistracking. What I want to know is whether a static charge
    could cause the electronics guiding the laser to misfunction slightly
    (a problem similar to the one I used to cause on my turntable by
    charging the dust cover when I cleaned it--and didn't realize was
    happening until the day that it pulled the tone arm straight up
    off the record until it stuck fast on the underside of the dust
    cover). 
    
    One more question: when the CDs are stored in the small boxes, the
    flanges that secure them in position seem to hold them up just slightly
    above the inner surface of the box. Wouldn't this encourage them
    to warp, particularly if the boxes are stored flat rather than
    vertically?
    
    Thanks for any ideas you may have,
    Jack Truslow
    

    Re/ .24:
    
    Re/ your second question:  I've often wondered whether CDs would
    be prone to scratching from being slightly rotated as the are removed
    from the jewel box.  If you do twist the disc slightly, and if the
    disc is in contact with the box lining, that would tend to cause
    circular scratches, the most deadly kind.  I've never looked too
    closely, but if the disc is actually NOT in contact with the box,
    that might alleviate that potential problem.

    As far as warping goes I wouldn't worry about it too much unless they
    are exposed to a significant heat source.  The plastic used in CD's is
    much less sensitive to heat than vinyl.