Journal of the Society of Motion Picture Engineers (1930-1949)

During re-recording it was found that the quality of the magnetic stripe was a faithful copy of the original magnetic recording. Apparently the processing of the photographic sound track had resulted in no ill effects on the magnetic track, which confirmed pre-production tests during which the characteristics of the magnetic sound track were checked before and after film processing. Normal overlap film splices were used in splicing this film. In running the magnetic sound track some of these splices proved to be silent and some noisy. It was found that magnetized shears and cutting blades of the regular film splicers were mostly responsible for this effect. It was also observed that certain splices had a microphonic effect upon the magnetic head due to the impact of the lower edge of the film splice upon the magnetic head. This last observation revealed that film splices were silent when made in one particular direction, which luckily happened to be the normal way of making splices on photographic film. The splice noise was eliminated by punching a diamond-shape hole (see Fig. 1) over the magnetic splice, as is done on photographic negatives. Another method was to notch the film at each splice and momentarily shortcircuit the recording system by a microswitch operated from these notches. Still another solution involved the momentary lifting of the splice from the magnetic head by the application of a triangular piece of adhesive paper on the splice. Some of the first samples of this photographic film exhibited severe edgewave and spoking of the film roll. These defects have long been present to a minor degree in standard motion picture film but were apparently exaggerated in adding the magnetic stripe to the base of the sensitized film. They have been largely removed through the cooperation of the manufacturer of the striping process. Another difficulty, pressure densitization of the photographic emulsion, due to too tight winding of the film rolls after adding the stripe, was also present in some of the early samples. This defect, too, has since been eliminated by more careful attention to proper rewinding of the coated film. The location of the balance stripe was also given some thought. Some film was manufactured with the balance stripe along the outer edge of the sprocket holes on the side of the photographic sound track. Other film was manufactured with the balance stripe located along the inner edge of the photographic sound track. Both positions were tried since at the beginning it was not1 quite clear whether the manufacturer's edge numbers on this film would be of any importance in film editing, and provision was therefore made to leave the edge numbers visible. Later, however, it was decided that these numbers had no particular significance and the balance stripe was moved to the outer edge of the film. In projecting the photographic track on normal projection equipment, it was found that the thickness of the magnetic stripe caused a slightly out-offocus condition which resulted in a loss of 1 db at 7,000 cycles. This was more evident when the balance stripe was placed adjacent to the photographic sound track because the magnetic stripe and the balance stripe were both riding the scanning drum, which caused the photographic film to be out of focus by the thickness of the magnetic emulsion. However, the later removal of the balance stripe to the outer edge of the film placed the photographic track in a more favorable position and practically eliminated this out-of-focus condition. Benefits of the Method The benefits derived by this method so far are as follows : 1 . It eliminates the need for introduc Frayne and Livadary: Photomagnetic Recording 395