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Consumer Electronics by S. P. Bali

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SOUND PICK-UP

The sound track pick-up is either advanced or retarded in relation to the picture to compensate for the physical displacement of the photocell or magnetic head relative to the picture heads as shown in Fig. 27.14 and 27.15.

When magnetic sound tracks are used on 35 mm or 70 mm film, the sound track is retarded or behind the picture. Optical sound tracks are advanced relative to the picture. In the first instance, it is termed pull-up, and in the second, pull-down, with reference to the picture aperture. For 8 mm projection, an optical sound track is advanced 22 frames, and for a magnetic track it is advanced 18 frames.

The actual displacement of the sound track will depend on whether the track is magnetic or optical. For reproducing ...

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