loudspeakers. Options are to use the two remaining magnetic tracks for subwoofer signals and/or split
(dual channel) surrounds.
The 35 mm format was modified during the 1950’s to handle four magnetic tracks: three screen
channels and a single surround channel. At the same time, the standard monophonic variable area
optical track was maintained. Figures
IA
and B show the channel layout for both 70 mm and 35 mm
magnetic standards. At present, the 35 mm magnetic standard is no longer in general use.
A. 70
mm
MAGNETiC
STRIPING
0.35
mm
A
I
’
Figure 1. 70mm six-track magnetic format (A); 35mm four-track magnetic format (B)
Figure 2A. 35mm Dolby Stereo Optical format
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