Cinematographic annual : 1930 (1930)

382 CINEMATOGRAPHIC ANNUAL contrast of positive development; (3) the optical conditions of reproduction; and (4) the electrical connection of the photocell to the reproducing amplifier. The Electrical Research Products, Inc., recommend that the development be checked by sensitometer strips measured in diffuse density. These are simply control measurements of the developing process. More detailed investigation shows that if the product of positive and negative gammas so determined equals unity, the sound record is satisfactory. If the ideally perfect development is departed from by an amount which makes a difference of no more than 20% from unity as the product of the gammas, the resulting sound will be free from any distortion which can be detected. A departure of 20% from the ideal processing will result in a harmonic, for every frequency, whose amplitude is 5% of that of the fundamental. Experiments in telephone transmission have shown that distortion no greater than this is indistinguishable from distortionless transmission. A corresponding variation in development of the picture would mean the difference between satisfactory screen projection and very harsh and dense prints on the one hand, or very thin and flat prints on the other, and it can be affirmed that the tolerance in the development of the sound track is considerably greater than that permissible for the picture. The application of methods of sensitometric control results in a greater uniformity in the final product, with less wastage than when inspection during development is relied on. In this way the demands of the sound track have led to improvement in picture quality and worked a benefit instead of a hardship. In Fig. 6 are shown enlargements of the sound records obtained in variable density recording.