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Synchronous Recording On '/4-In. Magnetic Tape
BY WALTER T. SELSTED
AMPEX ELECTRIC CORP., SAN CARLOS, CALIF.
SUMMARY: This article discusses the problem of synchronizing motion picture film with a sound track on standard %-in. magnetic recording tape. The equipment for synchronizing the tape with film is the major subject discussed.
THE USE of magnetic tape for recording motion picture sound tracks has by now aroused great interest within the film industry. The system of recording a sound track directly on optical film is unnecessarily costly and risky and will soon be obsolete. Only too frequently retakes are necessary because of failure on the part of a performer or in later film processing. Failure to get a perfect track results in a great waste of film, time and developing cost. Magnetic recording can replace film recording entirely for sound track work and will save the industry a great deal of money.
Early work with magnetically recorded sound tracks was done with standard 35-mm motion picture film coated on one side. Later, the film was split down the center to save one-half of its cost. However, the cost of split 35-mm magnetic recording film is ten times as high as standard J^-in. unperf orated tape. This difference in cost makes the latter recording medium appear to be most desirable if it can be used. Not only can it be used, but it has several other important advantages over the perforated tape, aside from that of cost. Storage space is reduced by 7J^:1 over the split 35-mm magnetic tape. Recording time per reel is increased by 2^:1. Weight per reel is reduced by
As everyone in the film industry knows, the problem of sprocket perforation flutter is a major problem which required considerable work to overcome. The use of J^-in. magnetic tape for sound track recording eliminates this problem as well. The manufacturers of magnetic recording materials have stated that the magnetic coating cannot be applied to 35-mm film as uniformly as it can on J^-in. tape. The greater uniformity obtainable on tape results in lower amplitude modulation of the recording and better high-frequency response. The 35-mm film base has approximately nine times the stiffness of K-m
PRESENTED: April 24, 1950, at the SMPTE Convention in Chicago.
SEPTEMBER 1950 JOURNAL OF THE SMPTE VOLUME 55 279