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MOTION PICTURE SOUND ENGINEERING
(b) Dimensions of Studio Push-pull Tracks
In the variable density Class A push-pull system, there are two
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location or APEeruec in valve pole puces
ALIGNMENT FLAT6
— Courtesy Electrical Research Products, Inc.
Figure 19 — Alignment flats of four-ribbon valve and associated optical system.
widths of sound track in current use in the studios: Regular (76 mils) and wide (200 mils). Regular push-pull occupies the same width as that of the original single track with the exception that there are two 35 mil tracks separated by a 6 mil septum, these tracks being scanned by the usual 84 mil slit. These dimensions are also used for push-pull movietone prints.
Wide push-pull tracks consist of two 90 mil tracks separated by a 20 mil septum. Each of these tracks is scanned by an 84 mil slit.
These three types of sound track, illustrated in Figure 20, have been adopted as Working Standards by the eight major studios. The dimensions shown in the larger sized numerals must be maintained as accurately as possible. Other values are nominal and for information only. The areas shown in black are controlled by matting the negative in the recorder — not by matting in the printing machine. This method, which limits the effective track width on the film itself, greatly reduces the effect of weaving in recorders, printers and reproducers. The volume reduction due to the slight decrease in track width in comparison to widths previously used, amounts to only a fraction of a decibel and is well justified by other advantages obtained.