Klarinet Archive - Posting 000062.txt from 2003/09

From: "Benjamin Maas" <benmaas@-----.com>
Subj: RE: [kl] Hybrid CD (long, technical answer)
Date: Wed, 3 Sep 2003 12:23:33 -0400

> -----Original Message-----
> From: Ormondtoby Montoya [mailto:ormondtoby@-----.net]=20
>=20
>=20
> Benjamin Maas wrote:
>=20
> > Hybrid does usually (but not always) refer to a
> > dual-layer CD with a SACD and a regular
> > (red book) CD layer.
>=20
> I'm struggling with the basic ideas. Does "dual layer" mean two
> different dyes, and each dye responds to a different wavelength of
> light, and therefore a CD player can isolate and 'read' one=20
> layer or the
> other, depending on the wavelength of its own light source?
>

Sort of... Commercially pressed CDs and DVDs are not made with a dye. =
It
is a completely different manufacturing process. In their case a glass
positive is made and is used to stamp out a pattern of pits in the =
plastic.
A layer of a reflective surface is added enabling the laser to reflect. =
The
differing reflection of the pits versus non-pits is what is used for the
transmission of data. =20

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.

Beyond this, I can't really explain much more... I'm not involved in =
the
manufacturing process. As a matter of fact, there is no way for even a
professional to make a SACD master at their studio. A data =
representation
of the disc has to be put on tape (like AIT or Exabyte) and sent for
replication...

--Ben

Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

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