Sony SQD-2020 - TECHNICAL DATA; WHAT IS THE SQ SYSTEM?

Frontal gauche
Left back
Arriére gauche "SQ" encoder,
Links hinten {Codeur “SQ”
Left front
Links vorn
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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
,
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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
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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.