Journal of the Society of Motion Picture and Television Engineers (1950-1954)

B. Electrical Performance Standards 1 . Frequency characteristics of reproduction. 16mm magnetic sound has up to the present time been largely of a dictatingmachine character in which the sound is recorded and reproduced on the same machine. This situation leaves the exact record characteristic up to each individual manufacturer since a complementary reproduce characteristic can be incorporated in such individually manufactured equipments. A situation of this kind is entirely unworkable on an industry-wide basis, since here a common understanding must exist in order to produce magnetic prints in laboratories for widespread distribution and reproduction on a wide variety of reproduction equipments. This situation is directly analogous to that existing in the production of normal 35mm film, and subsequently applied to 16mm photographic sound prints. This method of approach to the control problem is described in the Society's Tentative Recommendations for 16mm Review Rooms and Reproducing Equipment (pp. 116-122 of the January 1951 Journal). Briefly, the control now effective in the production of sound film does not specify the recording characteristic but does specify the reproduction characteristic, thus leaving the exact recording technique to the individual producer or equipment manufacturer. Such a method of control requires the production of a test film of known absolute values of discrete test frequencies. The methods for measuring such a magnetic film have not been evolved until recently* so that effective control of universal reproducibility of magnetic sound could not be established. These techniques are now being studied through the actions of the Society's Sound Committees, more specifically the efforts of Dr. John G. Frayne of Westrex Cord An engineering task group has beeij appointed by Glenn Dimmick to effecl compromises of such equipment varianceJ as may currently exist and to make ; recommendation similar to that preaj ently existing for 16mm photographiJ sound track and published as Tentativd Recommendations for 16mm RevievJ Rooms and Reproducing Equipment^ cited above. This recommendation will not re strict the frequency range of magnetic! sound track to that presently acceptable for photographic sound track. Tht actions proposed will not merely meet the immediate industry need for common action, but rather will anticipate the time when magnetic track may replace photographic sound track for highest quality reproduction purposes. The industry's need for early action i$' realized by all members of the task group and it is anticipated that a recommendation will be prepared for Sound Committee action by May 1953. It does not follow that industry needs will have to await upon such a formalization since the committee membership is comprised of sufficient representation to allow immediate application of committee findings to the current problems. 2. Intermodulation distortion film. In order to establish sound reproduction! listening conditions it is essential that there be a method of checking the reproducer and associated electronic amplification system as to freedom from distortion. This can be most conveniently done by an intermodulation test measurement. Film for this purpose has not been produced as yet, although methods for the production of it are now being considered by the Society's Sound Committee. This is an open item. C. Test Film Standards * J. D. Bick, "Methods of measuring 1 Multifrequency test film. This inter surface induction of magnetic tape," in locks directly with item B,l, above — this Journal on pp. 516-525. characteristics of reproduction. Suchi 528 April 1953 Journal of the SMPTE Vol. 60