Klarinet Archive - Posting 000073.txt from 2003/09

From: Umesh Shankar <ushankar@-----.edu>
Subj: RE: [kl] Hybrid CD (long, technical answer)
Date: Wed, 3 Sep 2003 16:47:57 -0400

Regarding the snippet of Ben's post below, I believe dual-layer DVDs are
made in a slightly different fashion from what is described. Also, using
both sides is separate from using two layers; you can have some
combination of each. Basically there really are two layers, one underneath
the other. The way the player can read both is that under the first data
layer there is a semi-reflective surface, so that the reader can either
read the top layer by reflecting off of it, or, by focusing further down
(and, I believe, using a higher-power laser) it can read the second
layer, behind which is a fully reflective surface.

Double-sided discs are easy to recognize because there is nothing
printed on them except in the little plastic ring in the middle. Since
I think many (all?) players make you flip it over physically to get at the
other side, using two layers is a preferred way of cramming more data
on the disc, but the option is there to use both sides and get twice
as much.

I can't speak to SACDs, and I'm not a professional expert so I could
be off a bit. Except for this point, I found Ben's post
characteristically excellent. I hadn't thought about the implications
of editing a DSD stream...

Ok, I just did a web search and here's the best I found on this stuff
(well, from the first Google result page ;):
http://www.eng.buffalo.edu/Courses/ce435/DVD/sld011.htm

Click on the right arrows to see each successive slide. It has nice
pictures.

Cheers,
Umesh

From: "Benjamin Maas" <benmaas@-----.com>
Subject: RE: [kl] Hybrid CD (long, technical answer)
Message-ID: <008b01c37237$b9406a00$3901a8c0@CIRCLE2>

Dual layer CDs and DVDs are made in a couple different ways. They
could have 2 size pits on the disc. Because there is so much more
data on a = DVD or SACD, the wavelength of the laser is much
smaller. (smaller "pits"). = The laser could focus on either the
larger or the smaller pits in the disc. Some DVDs do a dual layer by
having you flip them over... The former is what is usually done for
the so-called "hybrid" SACDs.

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