The Cine Technician (1953-1956)

THE CINE-TECHNICIAN January, 1954 COMPOSITE FOUR-TRACK SOUND STEREOPHONIC sound on film is not new in theory or practice. As early as 1937 the film industry produced a composite film using two optical sound tracks. The dual optical tracks were produced by dividing the regular single track into dual narrow tracks. This attempt proved unsatisfactory and was discarded in favour of a system employing separate sound and picture films. " Fantasia," the first successful commercial production using separate multiple-track optical sound film opened in New York City in the late thirties. Shortly after, World War II was upon us. At the close of the war a new medium for sound recording called magnetic tape had reached the point in development where its quality surpassed optical sound reproduction. The film studios were quick to realise the advantages of using magnetic tape for master recordings which were then transferred to optical sound track on film for general theatre use. This not only improved the optical sound reproduction but provided greater flexibility of operation and reduced production costs. With the advent of wide-screen picture presentation, stereophonic sound became a necessity and an ASA standard was set up providing for the use of separate sound film containing three optical sound tracks which was to be synchronised with the picture projector. This presented the studios and the exhibitor with many problems: (1) For uninterrupted projection, separate costly and space-consuming sound reproducing equipment was required for each projector. (2) The projectionist was faced with the problem of handling double the amount of film, plus operation of additional equipment and the ever-present worry about proper synchronisation. (3) Studio film production, inspection and sound synchronisation were extremely difficult. (4) Always there was the possibility of a mix-up in sound print and associated picture print reels as film is passed between exhibitors. (5) Loss of synchronisation due to film damage presented a difficult problem of rcsynchronism. General Precision Laboratory were approached by Twentieth Century-Fox early in 1953 to develop a composite film and associated magnetic sound reproducing equipment for not three but four sound tracks. Three tracks were to be used for left, centre and right behind-the-screen speakers for stereophonic sound and the fourth track for special effects to be projected through speakers placed around the theatre. To make room for the four magnetic sound tracks, the width of the sprocket holes was reduced to .078 inch. This was possible because the acetate base film now in use is tougher and does not shrink as much as the old nitrate base film. The picture width on the film was also increased somewhat. Two magnetic tracks were placed outside the sprocket holes and the other two relocated between sprocket holes and picture area. At first it was thought that the magnetic sound head should be located in the unit housing the optical sound head; however, this presented the following problems: (1) Optical scanning is completely frictionless since sound track is scanned by a narrow slit of light. Magnetic scanning, requiring intimate mechanical contact with the tracks on the film introduces friction, thus upsetting the stability of the scanning system designed for optical use. Extreme flutter and wow problems were the result. (2) With so many types of optical sound heads in use today, modification would be very costly and in many cases impossible. (3) After passing through the projector gate, where the film is exposed to intense light levels, each film frame buckles and such deformation seriously affects the subsequent magnetic sound scanning because of the absolute necessity of perfect contact between magnetic sound tracks and pick-up head. General Precision Laboratory engineers, after careful study, proposed to place the new multipletrack magnetic sound head between the upper feed magazine and the projector mechanism, thereby avoiding the aforementioned problems and adding the following advantages: (1) Scanning takes place while film is still cool and not deformed due to intense light, thus assuring the best possible magnetic sound reproduction. (2) Original optical sound head is left untouched and no compromise in sound quality is necessary in either system. (3) The clean-cut separation of magnetic scanning from optical scanning makes it possible to equip almost any theatre with a 4-track magnetic sound head for the new composite film regardless of type or age of its present optical sound system. The General Precision Laboratory proposal was accepted by the industry, and it was agreed that the placement of sound synchronisation 28 frames behind the picture would be standard. The first model was produced by General Precision and installed in the Fox Little Theatre in New York Citv in June of last year.