I have a CD whose label is off-center. Does this mean the music on the disc is
read off-center?

Thanks.

Farrell22 wrote:
I have a CD whose label is off-center. Does this mean the music on
the disc is
read off-center?

Thanks.

Hah! I just pulled out a used copy of "Noel," by Joan Baez, which I
picked up for $2 some months ago, and discovered that the label on side
2 had been put down, peeled off, and put down again. Far as I can tell,
neither attempt got it centered. But the record sounded OK.
(Orchestrations by PDQ Bach himself!)

LP holes can be off-center, and that can sound weird, but if a CD were
off-center the laser wouldn't be able to read it at all. Not to worry.
bob

if the recording track were actually off center i would have to guess
that in order to follow the track the laser would have to wobble to
keep it lined up. could this possibly cause wow or flutter or some
other kind of distortion? either that or it simply couldnt play the
track at all. this didn't seem to be the case. i used to work at
nimbus recordings manufacturing plant in virginia and any discs that
showed that type of problem were routinely trashed. most likely the
paper lable was the only thing off center. the only other problem i
could forsee would be the disc being out of balance and vibrating in
the drive sort of like an out-of-balance tire. that would also
probably effect the playback quality.

campdog wrote:

if the recording track were actually off center i would have to guess
that in order to follow the track the laser would have to wobble to
keep it lined up. could this possibly cause wow or flutter or some
other kind of distortion? either that or it simply couldnt play the
track at all. this didn't seem to be the case. i used to work at
nimbus recordings manufacturing plant in virginia and any discs that
showed that type of problem were routinely trashed. most likely the
paper lable was the only thing off center.

WHAT paper label?

Commercial CDs very seldom have paper labels. The "label" is printing,
on the plastic disc material.

Home-burned CDs sometimes have stick-on paper labels, which are sold in
stores, intended for the user to print them on a computer printer.
Incidentally, they are the Number One cause of CDs jamming in automobile
CD players, as the high temperatures often encountered in a closed
automobile parked in the sun can cause the adhesive to soften. If the
label lifts, it can jam the disc in its relatively narrow slot.

Of course, bearing in mind the following from an Audio Quackwatch post
to this newsgroup:

INTELLIGENT CHIP CD/DVD/SACD UPGRADE

"Machina Dynamica now carries the Intelligent Chip from Golden Sound.
The Intelligent Chip is a thin, orange, 1x1.5 inch rectangular wafer
that automatically upgrades any CD/DVD/SACD disc when the Chip is
placed momentarily on the top surface of the player above the spinning
disc.

.....perhaps a manufacturer will now produce a Magic Label that can be
adhered onto a CD to tackle this problem from a different approach.
Indeed, since some tell us that green ink on the edge of a CD results in
marked and miraculous improvement in sound quality, perhaps some
manufacturer will publish a White Paper (or Green Paper) describing
differing results resulting from different color labels being adhered to
a CD.

-Gene Poon

In article ,
"campdog" wrote:

if the recording track were actually off center i would have to guess
that in order to follow the track the laser would have to wobble to
keep it lined up. could this possibly cause wow or flutter or some
other kind of distortion? either that or it simply couldnt play the
track at all. this didn't seem to be the case. i used to work at
nimbus recordings manufacturing plant in virginia and any discs that
showed that type of problem were routinely trashed. most likely the
paper lable was the only thing off center.

Paper label? CDs don't have them, unless you stick one on yourself.
Prepressed CDs have a screen-printed graphic on one side.

the only other problem i
could forsee would be the disc being out of balance and vibrating in
the drive sort of like an out-of-balance tire. that would also
probably effect the playback quality.

CD drives are designed to deal with this since even near-perfect discs
have some vibration and/or warpage. The laser and its focusing optics
are mounted in a linear voice coil motor, allowing the drive to adjust
the distance of the laser from the disc. This serves as the focus
adjustment -- the lens itself has a fixed focal point and the entire
lens/laser assembly is moved up and down to place the focal point on the
surface of the disc. This assembly is controlled by a servo system
which keeps the laser focused at all times.

Note that this doesn't maintain playback quality so much as it maintains
the ability to play back discs at all. The amount of allowable slop in
the focal length is very, very small. If the system is out of focus,
the laser spot on the surface of the disc becomes too big to resolve
individual tracks, which of course means the drive can't read data at
all. So, the effect of actually losing focus would likely be big
dropouts, nothing subtle like changes in frequency or frequency
response, etc. (Most drives will insert silence whenever they can't
read data from the disc.)

--
Tim

On 11 Jan 2005 01:26:54 GMT, "Timothy A. Seufert"
wrote:

CD drives are designed to deal with this since even near-perfect discs
have some vibration and/or warpage. The laser and its focusing optics
are mounted in a linear voice coil motor, allowing the drive to adjust
the distance of the laser from the disc. This serves as the focus
adjustment -- the lens itself has a fixed focal point and the entire
lens/laser assembly is moved up and down to place the focal point on the
surface of the disc. This assembly is controlled by a servo system
which keeps the laser focused at all times.

On a point of information, one of the strengths of CD is that the
focus point is *not* on the surface of the disc, it's on the underside
of the metallised layer, more than 1mm beneath the reading surface.
This puts surface scratches out of focus and improves legibility of
the pits and lands.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article ,
Stewart Pinkerton wrote:

On 11 Jan 2005 01:26:54 GMT, "Timothy A. Seufert"
wrote:

CD drives are designed to deal with this since even near-perfect discs
have some vibration and/or warpage. The laser and its focusing optics
are mounted in a linear voice coil motor, allowing the drive to adjust
the distance of the laser from the disc. This serves as the focus
adjustment -- the lens itself has a fixed focal point and the entire
lens/laser assembly is moved up and down to place the focal point on the
surface of the disc. This assembly is controlled by a servo system
which keeps the laser focused at all times.

On a point of information, one of the strengths of CD is that the
focus point is *not* on the surface of the disc, it's on the underside
of the metallised layer, more than 1mm beneath the reading surface.
This puts surface scratches out of focus and improves legibility of
the pits and lands.

Yes, I glosssed over that, but it is definitely a big part of why CD
works as well as it does. A further benefit is that even if surface
scratches are so bad as to impact playback, it's often possible to
return the disc to life by careful polishing with appropriate plastic
polishing / filler compounds, etc.

About the only thing arguably wrong with this aspect of CD is that the
metal layer is much less protected on the other (non-optical) side --
there, it's covered by a coat of lacquer and a screen printed label,
neither of which are particularly thick. A scratch which breaks through
the lacquer can do serious damage to the metal. Even if it doesn't
cause immediate badness, it allows a path for oxygen to begin attacking
the metal layer.

DVDs solve that problem with sandwich construction; even single-layer
DVDs are constructed from two polycarbonate layers glued together with
the metal layer in the middle. This is visible on the inner surface of
the hub.

--
Tim