HHB comm CDR800 - Manual (Page 4)

Audio Electronics 2/00 35
The physical structure of a CD–R disc is
shown in Fig. 1. The recordable CD is
molded with a continuous groove spiral
from the inside to the outside of the disc’s
polycarbonate substr ate. The “pre-
grooved” disc is necessar y in order to
provide the recorder with a physical ref-
erence. The groove also contains timing
information that the recorder uses to
keep the CD spinning at the correct
speed at all points along the disc surface.
After the polycarbonate substrate is mold-
ed, the disc is spin-coated with the
recording layer, an organic dye such as
cyanine, phthalocyanine, or azo.
The recording layer is then coated with
a vacuum-deposited ref lective layer, fol-
lowed by a spin coat of protective lac-
quer. Most CD–R manufacturers add a
label coating to further protect the disc
from scratches. Special discs are available
with a label area compatible with an ink-
jet printer specifically made for printing
CD–R discs.
Inexpensive CD labeling systems are
also available, from a variety of sources.
Most of these allow you to print or write
on a circular label with adhesive backing.
These labeling systems carefully center
the label on the CD in order to ensure
smooth disc rotation. The adhesive back-
ing on the CD labels is compatible with
the materials from which the disc is man-
ufactured, and should not impair the per-
formance of the disc, or shorten its life. If
you label CDs by hand, you should avoid
solvent-based inks that could damage the
disc. TDK makes a pen specifically for la-
beling CDs, which you can purchase
from any pro audio dealer.
The recording laser beam is the same
wavelength as that used for CD play-
back—780nm. The laser i n the CD
recorder literally burns the organic
recording layer, momentarily raising the
temperature of the recording layer at
that spot to over 300
°
F. The width of a
burned area, the equivalent of a pit on a
prerecorded CD, is only 0.6 microns.
The burning alters the optical character-
istics of the organic dye, producing a dif-
ferent level of ref lection from burned vs
non-burned areas.
The most common organic dye found
in CD–R disc is cyanine. Azo dye, origi-
nally developed for types of optical
recording media, is also used for CD–R
discs. Cyanine and azo-based discs are
sensitive to ultraviolet light, as well as
heat and humidity. As such, their archival
life expectancy is only about ten years.
The recording surface of most CD–R
discs is green, while some appear blue.
This is due to the type of dye used and
the color of the ref lective layer. Silver and
gold ref lective layers yield a different
color when they ref lect light back
through the organic dye.
More recently, the Japanese firm Mitsui
has developed a CD–R disc using phthalo-
cyanine dye. These discs are gold in color,
in part due to the gold ref lective layer.
The phthalocyanine discs are far less sus-
ceptible to the degrading effects of light,
heat, and humidity, and are expected to
have an archival life in excess of 100
years. Mitsui is manufacturing these gold
discs for a number of other firms, includ-
ing HHB, and they have licensed the tech-
nology to other manufacturers as well.
Care should be exercised in the han-
dling and storage of all CD–R discs. Tests
have shown that the green cyanine-based
discs can be rendered unplayable if left
exposed to bright sunlight for only a few
days. Unless they are being recorded or
played, all CD–R discs should be stored in
their jewel cases at all times. The HHB
CDR–800 recorder automatically adjusts
the intensity of the laser beam to suit the
specific type of dye found on the CD–R
that has been inserted in the recorder.
All CD–R discs from reputable manu-
facturers are certified to meet “Orange
Book” specifications. The Orange Book is
a document produced by Sony and
Philips describing the technical specifica-
tions for the compact disc format. Part II
of the Orange Book describes the CD–R
for mat. You can find a considerable
amount of information on the CD–R
for mat on the websites of Maxell
(w w w.maxell.com) and HHB (w w w.
hhbusa.com or www.hhb.co.uk).
CD–R Basics
FIGURE 1: Cut-away view
of a CD–R recordable CD.
The pregrooved polycar-
bonate substrate is coat-
ed with an organic dye
recording layer and a re-
flective layer. During
recording, the laser beam
burns the organic dye,
momentarily raising the
temperature of the dye
to over 300
°°
F. A-1522-1