Advertisement
ABOUT CD.4
RECORD
In
conventional 2-channel stereo records, both
left
and
right
sound
information
is engraved
on the
left
and
right
walls
of
the 45"/45" record
groove.
If
this method
applies
to recording
4-channel sounds,
they must
be
converted
into
2-channel signals once
before
engraving
them
on the
walls. This
is
generally called
a
Matrix
4-channel record.
The
CD-4 disc record employs a special recording
and
reproducing
method
initially
developed in
Japan,
in
which
4-channel signals can
be recorded
independently
without
converting
them
into
2-
channel
signals.
The CD-4 disc record, two different kinds
of
signals
are engraved
directly on
each
left
and
right
wall (Fig. 21). One
signal
is the conventional
signal
with an
audible frequency less
than 15kHz,
and
engraved
in
the
same
way
as
conventional records.
Another
signal is an
inaudible
signal
of
a
frequency
higher than
20kHz.
If
such signals are reproduced
directly, they
are
inaudible.
In
the
CD-4 disc recotd, the other audible
signals
are converted
into
frequency deviation
between
20kHz and 45kHz (frequency modulation with
30kHz carrier),
and
engraved
on the
walls in
addition to the
signal
just
described.
The A-sound
in
the figure is
reproduced as
the
audible sound
when the stylus tracks the
groove.
TURNTABLE
With
CD-4 phono cartridge
However,
it
is
necessary
for
the B-sound to
use
the
demodulator.
The
X-signal
which
contains
the
B-sound is
demodulated
and
the B-sound
is
extract-
ed
from
the X-signal, thereby enabling the B-sound
to
be
audible.
In
the actual CD-4
disc
record, the A and
C sound,
which
are audible, contain
the
sum
signals
of
the
left front
plus rear, and the
right front
plus
rear
respectively. Therefore,
in
a 2-channel system, the
left
and
right
speaker systems can
reproduce
each
sum signal because
of its compatibility.
The
B
and
D
sounds,
on the
other hand, contain
the different
signals
-
the
left front
minus rear
and
the right
front
minus rear respectively.
For
a
complete 4-channel system,
the four
in-
dependent signals,
front left, front right,
rear
left
and rear
right
can
be fed
to
the amplifier through
the demodulator
and
the matrix circuitry
as
shown
inFig.22.
A-sound,
audible
(1
5Hz-15kHz)
lnaudible
X-signal
which
contains
B-sound
(20kHz-45kHz)
Fig.21
STYLUS
C-sound and
Y-signal
'7
which
contains
/
D-sound
REPRODUCED
SOUND
FIELD
Fig.22
A-sound and
X-signal
ORIGINAL SOUND FIELD
CD-4 ENCODER
CIRCUIT
DEMODULATOR
MATRTX
ClRCUlr
A
B
c
D
LF
FF
LEFr
8Rr
LR
Fn
r^w
A*B:(Lr*Ln)+(Lr-Ln)=2Lr
A
-
B
-
(
L
r
+L
n
)
(L r
-L
n
):2L
n
C+D:(R
r
+Rn
)+
(Rr
R n
):2R r
C-D:(Rr+'Rn) {Rr
Re):2Rn
Advertisement
