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

Edward Schmidt (Reeves Sounder aft Corp., Springda/e, Conn.}: I should like to point out that this question of high-frequency flutter affects not only the application of magnetic film in the motion-picture industry, but other industries as well. I was thinking of the telemetering applications of FM work and there is considerable work being done by all manufacturers of magnetic products to reduce or cut down on the head-scrape — that's about the best term that we've come up with so far. Perhaps it's coefficient of friction of the coating to the magnetic head. Dr. Frayne: I think that we did find that some manufacturers put out what they call a lubricated magnetic coating which does improve the high-frequency flutter performance. George Lewin (Signal Corps Pictorial Center] : Can anyone advise whether there is any individual adjustment on these multiple heads for head contact with the film? Mr. Athey: With the Brush head, which we are presently using, there is no way in which the individual contact can be adjusted, other than that the entire head can be tipped. It may be that as a result of wear, this individual adjustment may become desirable. At the present time, the attitude that we have taken (and I believe the other manufacturers, too) is that if the filter system is properly aligned so that the tension is equalized between the two sides of the film and the contact surface of the head is flat, then for all practical purposes the tension and head contact are consistent across the film. It has been very difficult to catch up with the theaters on life tests. In other words, in 24 hr you can't gain more than about 10 hr over a given theater. Our knowledge of the effect of lack of individual track adjustment as it affects the life of multiple-track, composite film is, I'm afraid, rather elementary. The present head is potted in plastic and it would be somewhat of a problem to do individual adjustment of, say, track 2 relative to track 1 and track 3. Mr. Lewin: I assume, then, that the adjustment for reproduction must be a lot less critical than for recording, because I know that in recording we probably would miss terrifically the absence of an individual adjustment for each head, since I don't think the film ever lies completely flat. Mr. Athey: I think I can use this as an occasion to make the point that in the beginning of this development there was evidence that there was amplitude modulation as high as 50%, 50 mils away from a sprocket hole. This evidence was based on the fact that a 200 or 250-mil track had been laid down and then played back with a 50-mil sampling head. Under our present CinemaScope conditions the track is laid down with a 50-, or eventually, a 60-mil head (I believe it's still a 50-mil now, isn't it?). The tension is localized in the individual area that you are concerned with. It's not the same process as attempting to keep the film absolutely flat across the 200 or 250-mil head, at part of which the contact may be poor. When you simply try to keep it flat over a 50-mil contact area, the problem does not seem to be as great. At any rate, this is our estimate from the results we have had. For example, when we had pieces of film which had had the edge wrinkled so that there was a definite kink, after a recording had been laid down, we could not hear this kink going through the machine. If the film were erased and an attempt were made to re-record, we just got a large hole in the sound, actually before and after this kink, as the film bounced clear of the head. The contact is, of course, more important on recording, because of loss of bias and the like, than on playback. I believe that the localized tension in the narrow track eliminates many of the difficulties that may occur with wider tracks, where the film is relatively stiffer. Mr. Lewin: My question wasn't so much whether the contact was uniform across the width of one head, but whether the film is going to lie flat enough so that when you got good contact in one head, you have good contact on the others, especially the ones in the middle. Mr. Athey: Would you estimate that the contact was going to be poor on the edge or in the middle? Mr. Lewin: Well, I would assume that if you have good contact on the two outside tracks, that the track inside, the one that's in the conventional photographic sound-track position, might tend to dish inward and have poor contact. 230 March 1954 Journal of the SMPTE Vol. 62