Dolby Laboratories SDU4 - Manual (Page 12)

2-5
controls are on the right-hand module, Cat. No. 344, as shown in Figure 2.5.
Figure 2.5 Cat. No. 344
Center Speaker Switch
Switch S301 allows the SDU4 to be installed in monitoring rooms that have
either two loudspeakers (labeled “center speaker, no”) or three loudspeakers
(“yes”). The factory setting is “yes.”
While decoding Dolby Surround with the internal switch in the “yes position,
the decoder’s Center output signal is sent to the center loudspeaker, as normal.
With the internal switch in the “no” position, the decoder’s center output signal
is divided and added into the Left and Right output channels, preserving a
correct phantom center image.
With the SDU4 set to MONO mode, the internal center speaker switch determines
where the mono output signal will be sent. With S301 switched to the “yes”
position, the mono signal (a sum of Lt and Rt) is sent to the Center loudspeaker.
In the “no” position, the mono signal is reduced in level by 3dB and sent to the
Left and Right loudspeakers, thereby creating a phantom center image.
The following charts summarize the SDU4 output signals in the mono, stereo
and Dolby Surround operating modes. Lt and Rt refer to the input signals.
L,C,R, and S refer to the 2:4 decoder output signals.
SDU4 OUTPUTS CENTER—LOUDSPEAKER SWITCH SET TO “YES”
Mode Left Center Right Surround
Mono — Lt & Rt — —
Stereo Lt — Rt —
Dolby Surround L C R S
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