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

Record Details:

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government concerned with film distribution the following objectives were established : (a) The overall quality of the sound should not be impaired. (b) The technique devised must be applicable to existing films as well as those to be produced in the future. (c) In view of the capital investment in projectors, any method of changing the character of the sound track must be accomplished through adaptation of available equipment. It was, of course, mandatory that any conversion unit applied to the projector must not, in any way, prohibit its use for projection of standard films. (d) The technique developed should insure an appreciable saving in print costs to the distributor and consumer. (e) The sound track supplied should be that prepared by the producer of the film and should remain a permanent part of the print itself. In view of the success achieved in reproduction of the 50-mil optical track portion of the striped magnetic sound systems, it was decided to concentrate on producing a double optical sound image each portion of which would be 50 mils in width. Either of these tracks could then be reproduced at will by simply inserting a suitable mask in the sound scanning beam of a 16mm projector. In preparing these dual-purpose sound prints it was found that two methods could be used. With the use of halfwidth masks alternately on opposite sides of the sound aperture and a double printing operation, the prints may be made from existing sound negatives by the processing laboratory. To avoid the double-printing operation, a similar masking technique may be used on an optical recorder. In this case two separate recordings are made in the standard single-track area on an interlock system by exposing one side, then reversing the mask, rewinding the stock and exposing the second half. Adaptation of Printers For the preliminary experimental work a double sound head Debrie Matipo printer was used. The alternate halves of each sound aperture were masked with brass shim stock suitably blackened to reduce reflection (Fig. 1). The Matipo printer is particularly suitable for this work since the sound gate is slightly undercut from the film path. Consequently a mask may be inserted in such a manner that it clears the moving film by about 0.010 in. To adjust the mask a standard negative is placed in its normal position on the aperture. Over this a piece of positive raw stock is placed so that the image of the track and the mask impinges on it when illuminated by the printer lamp. With the use of a toolmaker's microscope, the mask is moved to split the track at the 50-mil position. Fine centering of the mask image on the positive stock is accomplished by adjustment of the printer-lamp position. Figure 2 shows a section of multiple bilateral track from a Maurer recorder. The track is split in printing half-way between sections 3 and 4. Two samples of tracks printed and recorded in this manner are shown in Figs. 3 and 4. Figure 3 shows the result of mask overlap of approximately 0.010 in. which causes a loss of two tracks. Figure 4 illustrates a finer adjustment of the masks to eliminate the unexposed center strip completely. When it was established that the unexposed center area could be eliminated, an alternate use of this technique suggested itself. Instead of putting entirely different sound tracks on each 50-mil portion, it might now be possible to print or record different portions of the same track on each half-track portion. To check this reasoning a special mix of a sound track was prepared. The tracks to be mixed consisted of two music, and four voice and effects reels. From the dubbers the sound was fed Beachell and Graham: Dual-Purpose Optical Prints