CD-R quality (was Re: Shameless CDR vs CD questions)

[Paul Mather]

On 12 Feb 2008, at 9:04 AM, The Intelligentsia wrote:

> Just _what_ is the deal here???
> In my past experiences I have had 2 problems:
> 1) CD's with scratches either so deep or so many of them that they  
> cause the
> music to get "hung up", making a very fast rotational clicking noise
> 2) Ozric Tentacle's original Dovetail CD's having an apparent "ink"  
> problem,
> whereupon it would eat down into the cd, and cause the music to  
> become a
> horror noise rather than music
> *BUT THEN RECENTLY, I tried to copy some HW CDR's at a friend's, and  
> he's an
> ass, as well as a friend, so of course they were done at 4x normal  
> speed and
> DID NOT come out right*
> *come to find out, he can record actual cd's at 4x with no problem,  
> but NOT
> CDR's*
> *so what's the deal with THAT?????*
> *then we get to Trev's Max Effect CDR......not normal here either-    
> what
> mine does, is it has occasional drop-outs in the music, and will  
> tend to
> jump ahead in the tracks*
> *now admittedly my players are cheap, but they only malfunction with  
> this
> one- also, there are a fair amount of blemishes on it because he's a
> musician, and most don't know better, etc*
> *my point being: I thought none of this stuff was supposed to happen  
> with
> CD's/CDR's!!!  I thought only hang-up's would occur when too many  
> scratches
> or a scratch that is too deep is present*
> *fill me in folks, would ya please!!!!*

Here's the gist of it: CDs and CD-Rs use different physical  
technologies to encode the music layer and so are prone to degradation  
in different ways.  In particular, CD-Rs are less robust than CDs and,  
usually, scratches on the underside are the least of your worries.

Greatly simplified, CD-Rs are basically a shiny reflective layer with  
a layer of organic dye underneath, all encased in plastic.  Music is  
recorded on the disc by the CD-R drive laser operating at higher than  
normal read power.  The higher power causes the organic dye layer at  
that particular point on the disc to change its chemical properties  
and, importantly, to become optically different, reflectively  
speaking.  (That's why they call it "burning" a CD-R.)  So, altering  
the organic dye layer is how the 0s and 1s that encode the disc's  
contents (including music) are recorded.

This presents two major points of failure as far as disc longevity and  
playback quality is concerned: the quality (and stability) of the  
organic dye layer, and the toughness of the reflective label layer.   
If the reflective label side is easily breached or scratched this can  
cause damage because at those points on the disc there is now nothing  
to reflect the read laser back.  So, discs with tougher reflective  
layer sides are better.

If the organic dye layer degrades then this leads to a general  
increase in the Bit Error Rate (BER) of the disc.  Once the BER  
becomes too high (to be compensated for by the built-in error  
correction capabilities of the CD format) then you start to get  
playback problems.  The organic dye layer can degrade for a variety of  
reasons: poor storage; excessive heat or humidity; etc.  Remember,  
though, that the organic dye is a chemical and so, as with all  
chemicals, can vary in quality due to the materials and processes that  
go into manufacturing the chemical.  So, low quality dyes may not be  
as stable over the long term and might degrade faster than higher  
quality dyes.  (A lack of stability causes the optical properties to  
degrade over time; 0s degrading into 1s; etc.---somewhat similar to  
the "CD rot" that afflicted the Ozric Tentacles Dovetail pressed  
CDs.)  Low quality dyes might also make the original recording of a  
lower quality in the sense that it is closer to the acceptable margins  
of engineering tolerance (pits and lands size, etc.) allowed by the CD  
format.  For example, if a dye is lower quality, it might not change  
its state well-defined enough when burning at high speed, resulting in  
a recorded disc that is already at the margins.  Such discs will be  
harder to play on a variety of different hardware and are less likely  
to have as long a useful life.

As for underside scratches, the ones that do the most damage are the  
ones that run parallel to the CD spiral direction.  Ones that radiate  
straight out from the centre to the edge are the least damaging  
because they affect less contiguous runs of bits, and so are the  
easiest to overcome via the CD format error correction.  Likewise,  
surface scratches that are not too deep are usually not problematic  
because the laser focuses past them and so, optically, they don't  
present much of a challenge.

To sum up, even though lots of people will no doubt disagree, the main  
factor on the LONG TERM life of your CD-Rs is the quality of the disc  
and how it is stored.  Buy good quality discs and you will have less  
problems.

Again, this will probably kick off an argument, so take it for what  
it's worth, but the usual rule of thumb is to try and avoid "Made in  
Taiwan" discs and look for "Made in Japan" discs.  There is a big  
quality difference in the fabrication plants and the consensus is that  
the Japanese ones are higher quality.  There aren't that many  
fabrication plants and most of the varieties of discs you see are just  
companies branding product from some fab or other.  Unfortunately,  
most of the discs you find in the shops are of the made in Taiwan  
variety.  In the interests of full disclosure, I buy unbranded Taiyo  
Yuden discs.

I hope this helps.

Cheers,

Paul.

e-mail: paul at gromit.dlib.vt.edu

"Without music to decorate it, time is just a bunch of boring production
  deadlines or dates by which bills must be paid."
         --- Frank Vincent Zappa