Sony SQA-2030 - Page 12

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 produces
four-channel signals after being processed by a decoder.
Fig. 1
LEFT FRONT i
ae O LT=Lf-j0.707Lb + 0.707Rb
LEFT BACK sa
RT
HIGIE BARK Encoder O RT-~ Rf -j0.707Rb - 0.707Lb
RIGHT FRONT
The SQ encoder takes the four channels of information from a
four-channel master tape or from a “live” pickup, and combines
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).
Pickup stylus tip
7
Right channel
modulation
N
Left channel. \/ 4
modulation
™.
7
Position of modulated groove
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 the 45-degree
lines exactly as in two-channel recording (Fig. 2).
Fig. 3
,
Y
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Vv
Left back modulation Right back modulation
Fig. 4
Left front
Right front
Left back
Right back
12
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 counterclockwise direction
(Fig. 3). As the record moves under the cutting sytlus, the
circular motions leave two oppositely-directed helical groove cuts,
(Fig. 4).
This unique stereo modulation system allows the SQ decoder to
clearly sensé 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.
Fig. 5
Left Total O Lf+0.707Rb—j0.707Lb
O
“sa” © Lb +jO.707Lf-.0.707Rf
Right Total
Oo
Decoder OQ Rb+ 0.707Lf—j0.707Rf
RE__© pfs jO.707Rb-—0.707Lb
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 and right back
speakers, respectively.
The final result of the encoding and decoding, as shown in Fig.
5, is that each speaker gets a signal 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 directionality.
In the SQA-2030 decoder, additional circuits are used to elimi-
nate 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 signal
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 predo-
minant signal information comes from the front or back, and
increases the level of the predominant signal information.
The results are clear in only a few moments of listening. The
music is in front, to the right, in back, or wherever else the
composer intended it to be, and it stays in its assigned position.
The listener gets the four-channel experience to the fullest extent.