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648 J. A. MAURER [j. s. M. P. E~
in frequency range and volume, all records made from negatives of densities between about 1.0 and 1.6 will give identical results if the prints are made to a density of approximately 1.3.
If for any reason a negative of low density must be used, the result will be different to the ear only in that the volume is slightly reduced.
Variations in development of the records have no effect except as they change the density.
These results confirm the impression which has come from practical experience, that the variable area type of record permits very wide latitude in photographic treatment without sacrifice of quality in the sound.
DISCUSSION
MR. E. D. COOK: I was very interested to hear this excellent paper by Mr. Maurer. There are two comments I should like to make. One of them relates to the name that has gripped us in regard to this type of recording. In applying a name we ought to accept the name from the ideal. In so far as the varying area is present, it only contributes distortion and it would seem desirable to stick to the older term of "variable amplitude."
The second comment is relative to my paper before the New York branch of the Society, at which time I had no opportunity to reply to discussions on the calculation of slit effects. I am pleased to know that Mr. Maurer has come to this same conclusion; the effect is quite serious.
MR. TAYLOR: I was going to endorse what Mr. Cook said until he called it "variable amplitude." Amplitude is measured in a great many ways. "Variable width" appears to be a better term.
MR. PALMER: I have one question about the density of the sound track negative. It seems to me that in a system such as he described it should be very easy to produce a negative of a desired density and do that consistently because of the fact that you are using a constant candle power, and I don't understand why there should be so much variation in density on the sound track negative.
MR. MAURER: It is extremely easy to control the density of the sound track within much narrower limits than those I referred to in my discussion. Ordinarily, I believe those limits are 1.3 to 1.4 or a range somewhat similar to that. The reason it is not a simple matter to keep the density where we want it is that in order to obtain the advantages of high resolving power we have gone to the slowest film at high contrast in order to keep down high frequency losses. With this high contrast a smudge of finger grease on a lens cuts down density noticeably. The wide range referred to in my paper was to show that this wide range has little effect on the quality of the reproduced sound.
MR. SHEA: I think it is very interesting to have a paper on the proper processing conditions with the variable area method. For a considerable time an impression prevailed that little attention had to be paid to the proper choice of processing for variable area recording. I think that has been dissipated, and the fact that it has been is nothing against the method. Curiously, some of the chief benefits are in processing. The technic whose optimum has resulted in