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Frontal gauche
Left back
Arriére gauche
"SQ" encoder,
Links hinten
{Codeur "SQ"
Left front
Links vorn
© LT =Lf-jO.707Lb +0.707Rb
$Q-Kodier-
gerat
Right back
Arriére droit
Rechts hinten
Right front
Frontal droit
Rechts vorn
RT
ORT =Rf +j0.707Rb —0.707Lb
Fig. 1 Abb. 1
Left channel *
Modulation du ™-
Modulation du
canal gauche
Position of modulated
groove
canal droit
Linke Kanal-
Position du sion modulé
Rechte Kanal-
modulation
Modulierte Rillenflanke
modulation
Stylus tip
Pointe de stylet
Nadelspitze
y
"Right channel
,
SOF
v
Fig. 2. Abb. 2
Left back modulation
Right back modulation
Modulation
arriére gauche
Modulation arriére droite
Linke Hinter-Modulation
Rechte
Hinter-Modulation
Fig.
3 Abb.
3
Left Front
Frontale-gauche
Links-vorn
Right Front
Frontale-droite
Rechts-vorn
Left Back
Arriére-gauche
Links-hinten
Right Back
Arriére- droite
Rechts-hinten
36
Fig. 4 Abb. 4
TECHNICAL
DATA
WHAT
IS THE SQ SYSTEM ?
In the SQ system,
a quadraphonic
program
is converted
into a
two-track program by an encoder prior to cutting the SQ record.
During playback, the encoded
program
on
the
SQ
record
pro-
duces four-channel signals after being processed by a decoder.
The SQ encoder takes
the four
channels
of information
from
a four-channei
master tape or from
a "live"
pickup,
and
com-
bines
them
into two which
have the following
characteristics :
The
left encoded,
or "total"
channel
contains
the
left-front
signal unaltered,
plus reduced
amounts
of the two back channel
signals, with phases altered.
The right "total" channel
has the right front
signal
unaltered,
plus, reduced
amounts
of the two back channel
signals, but
phases shifted with relation to the back signals in the left total
(Fig. 1).
When
the
two
total channels
are applied to the stereo cutter,
the left front and right front signals
are
recorded
on
the two
side
walls
of the groove
by cutting-stylus
motion
along
45-degree
lines, exactly as in two-channel
recording (Fig. 2).
Each
back
signal,
however,
(since
it appears
in
both
total
channels
but
with
a 90-degree
phase
difference
between
the
two
versions)
produces
a circular
motion
of the
stylus,
with
the stylus motion for one back signal circling in the clockwise
direction and the motion for the other back signal in a counter-
clockwise
direction (Fig 3).
As the record
moves
under
the
cutting stylus, the circular motions leave two oppositely directed
helical groove cuts (Fig 4).
This unique stereo modulation system allows the SQ decoder to
clearly
sense
the
phases,
as
well
as
the
amplitudes,
of
the
different
components
of the total signal.
The record
is played
with a standard
stereo pickup,
and the two
total signals
go to
the decoder.
Figure 5 shows the decoder action schematically.
The left total
signal goes straight through to the left front speaker, the right
total to the right front speaker.
In addition, the decoder makes
two
different
combinations,
or
matrixings,
of the two
total
signals,
to produce
two
more
outputs,
for the
left back
.
tight back speakers,
respectively.
The final result of the encoding
and decoding, as shown
in Fig.
5, is that each speaker gets a signa! in which the channel for
that
speaker
position
is dominant.
Each
speaker
also
gets
"side-effect" signals, inevitable in any matrix system.
The crux
of good matrix design is to so dispose of the side-effect signals
that
they
do
not
prevent
the
establishment
of firm direction-
ality.
In the
SQD-2020
decoder,
the following
two circuits are used
to eliminate the "side-effect" signals so that excellent separation
between
all four channels
is obtained.
A waveform comparator
circuit
detects
the
predominant
signal
information
by
signal
strength
and
phase-angle
relationships,
increases
the
level of
this signa! information and reduces the level of the "side-effect"
signal information.
Therefore,
excellent
separation
is provided
between
all four
channels.
To further improve
the front-back separation, front-
back logic circuitry operates to detect whether the predominant
signal information comes from the front or back, and increases
the level of the predominant
signa! information.
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