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fact that the diazo materials never seemed to reach a very high density. So in this particular instance, the most trouble they had was with the signal-to-noise ratio. I would like to know if in the new experiments anything better has been achieved.
Mr. Hill: There has been a good deal of work done on that aspect simply for the office copying use of diazo on paper in trying to get a better and more opaque black, and I'm sure that some of those things have given us combinations of dyes which are better than we had, say, twelve or thirteen years ago. It is that total density that they're trying to improve, but as with any of the dyes, where you have a black dyestuff for cloth or any other purpose, you really have a very dark color rather than a true black. In the same way with the diazo coupling, and as I mentioned before, there is a faint fading going on so that when you've got a total density that's still a little less than you want and then it starts to fade, you've still got trouble. But I'm sure that some of the dyes that have been worked out in the
past four or five years are much better than they've had before.
Mr. Zjambuto: Could you give us any figure as to the amount of signal-to-noise ratio that was achieved?
Mr. Hill: In that case I can't. The stuff I have seen has been on paper materials. We've been involved in the basic chemicals rather than in the application, so that we don't have that part of it going through our lab. But we do have the basic chemicals and their coupling to get a black, black as possible on paper.
Mr. Offenhauser: As I remember it, we had something like 60-db signal-to-noise ratio and something less than 2% harmonic distortion. The figures can be obtained, I believe, from Andre Schoen in Binghamton; he has the logs and test data. We would never have contemplated using these materials for FM transmission unless the performance was that good or better. We used blue-sensitive photocells with matching dyes; these latter were peaked in the same general spectral range. We tried many dyes and cells experimentally; the blue combination proved to have the best performance at the time.
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July 1952 Journal of the SMPTE Vol. 59