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SOUND-EECORDING MACHINE 239
tion in either the left-to-right or the right-to-left directions. Such operation is essential — and is so recognized — to cope effectively with the problem of emulsion position in contact-printed release prints. The flutter of the RCA PR-32 is rated at less than 0.15%.
In the Maurer sound-recording machine (Fig. 52) the film also moves past the exposure light beam on the surface of a smooth drum; on the other end of the shaft that carries the drum is a large flywheel, as in the RCA machine. The filtering of motion of the Maurer machine is in two stages; the drive gear is coupled to the flywheel hub by resilient felt or similar bushings, and the flywheel hub is coupled to the flywheel itself by an oil film. Flutter of the Maurer machine is rated at less than 0.05%. This new machine has a larger flywheel and a larger drum than its excellent predecessor, the Model D machine ; the flutter has been reduced to about one-half its previous value. The hydraulically-coupled flywheel arrangement was pioneered by Kellogg of RCA. "Western Electric machines of current manufacture also have an excellent transport system of a generically similar type.
When well maintained, both the RCA and the Maurer recording machines have excellent film motion; it is far superior to the film motion found in any commercial sound projector. ' Flutter may be checked readily by recording a 3000-cps tone at constant amplitude, developing the film, and measuring the flutter with an RCA or Western Electric flutter bridge or equivalent with the film being reproduced on a special ' * grindstone" type of test reproducer. Recording equipment manufacturers customarily make such tests in a routine manner when sound-recording machines are manufactured. The machine used for reproducing is usually made with great mechanical precision; one type commercially used has a 60-pound flywheel coupled directly to a drum that revolves twice or less per second; the drum has an eccentricity of only about one-tenth of a thousandth of an inch. Needless to say a flutter film recorded on such a grindstone and reproduced on such a grindstone has so little flutter recorded in it that it is possible to make an "A-B" test by switching quickly from an oscillator to the film without observing aurally any difference in film motion introduced as flutter. Testing the smoothness of motion of a recording machine is customarily made in accordance with American Standard Z22.43-1946, "3000-Cycle Flutter Test Film." Much attention has been given to the study of uniformity of film motion ; the machines made by major film recording machine manufacturers may be relied on to be satisfactory in this respect. In practice,