1.3.2 Handling
and care of
the
compact
disc
Handling of the compact disc is more
convenient and trouble-
free
than
is
the case with LP
records.
However, it is
still
essential
to observe certain
precautions
which
can be
better
followed if
the mechanical
design of the compact
disc
is
understood.
The
compact disc consists of three layers.
A
relatively strong
transparent substrate is coated with
an ultrathin aluminized
lay-
er on which the information is encoded.
The label
(content,
art-
ists,
disc brand)
is
printed
on this sensitive layer. Thevarnish and
the ink
applied during the
printing
process
are the only
protec-
tion of the aluminized layer. Although the laser
pickup
"reads"
from the opposite
side.
which is the much
better
protected
side,
a scratch on the
printed
side of the aluminized layer can
interfere
with or even
prevent playback
of the
compact disc.
The
pitch
of
the information
"grooves"
on
the
compact disc
is
only
1.6pm
and the average bit length
is
approximately'1
pm
(:'111000th
of a
millimeter). ln view
of
these microdimensions
it becomes clear
that a
scratch
on
the
printed
side of the compact disc can
have
disasterous consequences.
On
the read side
(scintillating
surface), a
scratch
or
fingerprint
has little
or
no effect. This side
is largely
protected
by
the strong
substrate. The laser
pickup
is not
easily
confused by scratches
and contaminations.
Because of
the strong
focussing, dirt
par-
ticles on the CD surface cause little interference.
Despite this. compact
discs should
be
handled carefully and
kept clean in the same
way
the
hi-f i
enthusiast
is accustomed to
from LP records.
Cleaning of the compact disc
is
not necessary if the CD
is only
touched along the edges
and if it is immediately returned to the
origina
I
jacket
after it has
been
used. Dirty
compact
discs can be
cleaned
with a lint-free,
soft
piece
of cloth.
Never
use
any sol-
vent or abrasive cleaning agents.
,l:
s
*
1.3.3 Structure
of
the compact
disc
A
great
abundance of
information
is
stored on a compact disc
The
user
gains
full advantage of
the
possibilities
offered by the
CD system only if he knows
the structure
of the
compact
disc.
The maximum
playing
time of a compact
disc
is
approximately
70 minutes. This
makes
it
possible,
for
example, to
play
Iong
concerts
without interruption. However,
because
it is frequently
desired to search
and
play
individual
passages,
corresponding
information must
also be encoded
on the audio track.
The
fol-
lowing
methods are
used on the compact
disc.
-
lf the
content can be subdivided into
individual selections.
these are separated
by short silent
grooves.
On the
compact
disc these
selections are
identified
as TRACK
-
A
different
method
of subdividing is
the use
of
indices
(lN-
DEX).
Classrcal recordings in which
most works consist of
movements
are
provided
with indices
by some of the disc ma
n ufactu rers.
Note:
The subdivision
of
compact
discs is
def
ined
bythe CD manufac-
turer.
On
recordings
comprising
severai
sections
for which no
indices have
been created.
the starting
time
(CD-TIME)
is usual-
ly specified on the
jacket.
-
Each
compact disc is
also subdivlded into minutes
and se-
conds of
play
time. Any location
can, therefore,
be accurately
and
reproducibly
accessed
The time indicated
on the display
of the REVOX 8225
ts always read
f
rom
the compact
disc and
does
not
correspond
to the actual
playing
time of the unit.
Of
course, any location
can be
searched
in
TRACK TIME as well
as in CD TIME mode
(refer
to Section 2.3
"Caution").
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