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

in his opinion rapid progress is being made by the various Society Committees and their actions certainly auger well for the future of 16mm magnetic sound recording and reproduction. Editorial Note The foregoing paper originally included between the present B-l and B-2 sections several paragraphs discussing production techniques for magnetic standard signallevel test films. During review of the paper by members of the SMPTE Sound Committee and Magnetic Sound Subcommittee it became apparent that this discussion needed modification to bring it into agreement with certain considerations which have developed since the paper was presented. Inasmuch as Dr. Frayne has been very closely connected with these, Mr. D'Arcy and he agreed that the original paragraphs should be deleted and the following addendum, prepared by Dr. Frayne, be published: Standard Magnetic Signal Film. The recording and calibration of a standard signal-level photographic sound track have constituted a very valuable adjunct in the lining up of photographic reproducers, and it is thought that a similar magnetic standard signal-level film would also be of equally great value. Methods of calibrating a standard signal photographic level film have been developed over the years, and there is quite general agreement now as to the interpretation of such films. The production of such a film on a magnetic medium is in itself rather simple, provided certain parameters are specified. If, for example, a 1 % distortion is considered a desirable maximum recording level, then it is a relatively simple matter to record a standard frequency at 400 or 1000 cycles which would on reproduction show a distortion of this amount. There are, of course, various ways of arriving at such an overall distortion, the final result depending on such things as the amplitude of the highfrequency bias and the input level to the head. However, these recording techniques are now quite well established in the motion picture industry, and there should be no problem to making such a film to meet the 1% distortion specification. If the absolute level in terms of magnetic induction of such a film is desired, this caul also be obtained using some of the calibra-J tion techniques currently under consider-t] ation. It is doubtful, however, whether anl absolute calibration is desirable in terms of;| units of magnetic induction since it would'] mean very little to the user of this filmJ under practical testing operations. Possibty such a master film could be made and1 retained by the supplier of the test films — the thought being that the production test films could be calibrated against this master film. Discussion George Lewin (Signal Corps Photographic \ Center): At the meeting of the Magnetic j Sound Subcommittee earlier in the week I made a remark, more or less with tongue inJ cheek, which perhaps I should repeat, now that possibly representatives of all four of the major producers of magnetic striping J are present. The remark was that it doesn't seem entirely impossible that magnetic-striping material could be made transparent or semi-transparent, in which j case you could always make it full width i and thus eliminate most of these problems \ we have about half-track versus full-track. I Mr. D'Arcy: May I suggest that that be | answered by some of the striping people! here? . . . No response? Mr. Lewin: The fact that one of them has { announced an oxide which seems to be 1 0 i or 12 db more sensitive may indicate they could afford to disperse the particles a little bit more and give up some of that sensitivity in the interest of making the \ coating transparent. Mr. D'Arcy: Would you like to answer • that, Dr. Wetzel?. . .No, I don't believe Dr. : Wetzel has an answer to this suggestion at the moment. Maxwell A. Kerr (Bureau of Ships): It has just occurred to me this afternoon that perhaps we have a blessing in disguise in the practices discussed earlier about the location of magnetic half-width stripes on a photographic sound tracks. If by chance or by deliberate planning we regularly alternate the half-width stripe position, head wear would be equalized by the : general use of various films, so why > standardize on just one side for half-track? We have recently been informed by one organization doing striping that half 530 AprU 1953 Journal of the SMPTE Vol. 60