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

jjand by our Armed Forces, who plan exijtensive use of pre-recorded magnetic tracks. I As is the case in all SMPTE activities injvolving the formulation of standards, parijticipation in the work of the sub-subcomjmittee is open to all having a legitimate injterest. Such persons and organizations jnot currently represented are requested to [{communicate with Mr. D'Arcy, or with IJMr. Dimmick or Mr. Milliard of the parent groups. Dr. W. W. Wetzel of Minnesota Mining J& Mfg. Co. answered questions from I George Colburn (Geo. W. Colburn Laboratory) as to the reason for supplying the |3M laminating tape in quarter-inch width, with the excess beyond the desired track width being slit off after laminating. It is I primarily to insure easier handling in the machine due to the greater tensile strength, land to permit the same machine to apply [any of the track widths (100-mil, 50-mil, J32-mil) currently in use. The laminating Icement is thermal-plastic and hence the Ijslit-off portion of the tape can be re-used so long as it is 100 mils or more wide. M. G. Townsley (Bell & Howell Go.) initiated a considerable discussion on head width versus magnetic-track width by expressing a feeling that the matter of differential wear caused by tracks narrower than heads is not nearly as serious as has been forecast in some quarters. True, it cannot be ignored, particularly in special cases | where narrow tracks run always in the same position relative to a wider head. Even such cases may well be of little consequence in the future, however, due to the imminent advent of magnetic-head materials with enormously greater wear resist| ance than the present soft mu-metal. Discussion between John Hilliard, Dr. I Wetzel and others brought forth the in1 formation that heads narrower than tracks jhave the advantages of less amplitude | modulation due to track width variations, i they allow for some film weave at the scanning point, and they avoid possible head/ i track contact difficulties caused by having the head ride the extreme edges of the | track, which frequently have ridges, varying \ slopes, or other discontinuities in the weti coated types of tracks. Dr. Wetzel subsequently called attention, however, to the fact that laminated tracks have very flat, [sharp edges, and track widths can be con trolled with great accuracy. Assuming that highly wear-resistant head materials become available, a head wider than the widest track to be reproduced, in combination with laminated tracks, would have the extremely important advantage of being able to reproduce any width track with maximum output level and with complete freedom from the effects of film weave. Current Status As stated in Mr. D'Arcy's paper on standardization needs, the establishment of a standard reproduce frequency characteristic for 16mm magnetic sound tracks hinges upon the availability of magnetic frequency test films having known absolute values of magnetic induction at each frequency so as to permit separation of the reproduce characteristic from all other factors in the record-reproduce process. Actually, the job of reconciling existing differences in reproduce characteristics between machines of different manufacture could probably be accomplished reasonably well without test films of absolute calibration, provided all measurements were made with the same film (or with carefully recorded exact duplicate films). Much more confidence in the results, however, and better agreement as to their validity will obtain if independent means are available for determining the absolute values of magnetic induction. Fortunately such means have very recently become available. In the months since the Washington convention sample frequency films have been produced by Edward P. Ancona, Jr., at RCA's New York film recording studio, and by G. G. Davis at the laboratories of Westrex Corp. in Hollywood. Both films were calibrated under Dr. J. G. Frayne's direction, using the short-gap method mentioned in the J. D. Bick (RCA Victor Div., Camden, N. J.) paper on methods for measuring surface induction which is published in this Journal issue. Earlier it had been found that the wide-gap calibration technique, which gave good results at 35mm film speed, was not at all satisfactory at the 16mm speed. After taking into account the somewhat more complex recording equalization used in producing the RCA film, the two films running in the same reproducer (with azimuth adjusted to suit the individual £. W. D'Arcy: Standardization Needs 533