Why CDs are more Rugged than CDRs

Date: Fri Mar  5 07:48:18 MST 1999
From: Tracy Valleau <tracy@linksware.com>
Subject: Why CDs are more Rugged than CDRs

Yes, the most fragile part of a CDR is the TOP, which can be easily scratched, and thus will destroy the CD data, since it's the underside of this layer that is altered by the laser.

CDRs are created not by pits (which CDs are pressed out in a big stamper, just like records) but by altering the reflection on the lower layer by burning the chemicals there. Pits redirect the reflection of the laser off the pickup, whereas the CDR burned ones simply fail to refect enough light to trigger the circuitry.

The reason your music CDs are more rugged than CDRs is that they have a wee tiny layer of plastic on top of the aluminum foil the pits are stamped into. CDRs have nothing on top. (Well, what's on top has no bearing on what's on the underside of the top, that receives the laser burn. It could be white for printing; silver or any other color.)

Lasers themselves have different frequencies, as do the pick photodiodes (as I understand it.) So, for earlier laser players, the contrast between the green, and the "burned" green was not sufficiently different to provide a reliable trigger.

Silver is the "hot new" color; gold is always popular, and deep blue is quite reliable. (You might think that there'd not be much contrast on the deep blue, but remember that lasers don't necessarily use the visible spectrum...)

OK: perhaps too techie for a Director list, except that most of our stuff ends up on CDs, so we ought to understand them a bit, no?

cordially,

Tracy Valleau
Digital Light Studios, Inc.
http://www.DigitalLightStudios.com/

A Different Opinion

Date: Thu, 18 Feb 1999 19:19:08 +0000
From: alyssa6 
Subject: Differ Opinion

Just wanted to give you a different opinion.

In Eugene, Oregon there is a Sony CD production plant. At Digital Image Productions we made a CD for a company called Percon. We had the CD reproduced at Sony, about 5000 on the first run in September 98. I took one of the CDs from Sony and scratched the back of it and it was damaged just as easily as any of my TDK or Mitsumi CDRs. The quality is exactly the same for both CDs and CDRs. Although I have not intentionally scratched a music CD, you can still see your finger nail making an impression through the back layer onto the foil, just like in computer CDs and CDRs. Summary: the only difference I have found between CDs and CDRs is that you can write on a CDR and the method of recording on a CDR is chemically based. I am going to call Sony and find out how they are reproducing CDs but I suspect that it will not be much different than how we do it.

Vaughn Anderson
Digital Image Productions