Cinematographic annual : 1931 (1931)

190 CINEMATOGRAPHIC ANNUAL The proponents of toe recording for sound records have usually advocated a negative visual transmission of 50 per cent, printed to a positive visual transmission of 50 per cent, with negative and positive gammas as in Fig. 8. It appears from the preceding discussion that the unmodulated negative transmission is not limited to this value although the appropriate printer point yields the same positive transmission for each negative unmodulated exposure within the permissible range. Based on the above conclusions, a toe record on Eastman positive film was made with the light-valve, setting the recording lamp to result in an unmodulated track density of 0.30 visual diffuse when the negative is developed to a daylight time scale gamma of 2.0*. Following the usual recommendations for toe records this was printed to a positive track density of 0.30 visual diffuse, the print being developed as had been the negative. These requirements were exactly met at the Fox Laboratory. A daylight time scale exposure on the negative was printed through on the positive. The printed-through densities were measured and converted to projected densities by the projection factor, 1.25. This over-all curve in terms of projected print density vs. log negative exposure in meter -candle-seconds was translated into projected print transmissions vs. negative exposures and the open circles in Fig. 9 show how closely the actual result agreed with the expected. Perfect agreement would locate the circles on the curve in Fig. 9 at printer point B. This check appears satisfactory to vindicate the construction employed and the considerations on which it is founded. The record showed excellent quality for both speech and music. Limitations of toe recording remain to be discussed, but the emphasis at this point is upon the fact that, by properly choosing the negative exposure, negative modulations, and printer point, a processing which is pictorially useless gives a result which is acoustically excellent. A claim made for toe recording is that the sound negative, when projected, is of as good quality as the print to be made from it. In Fig. 10 the negative curve in the lower right-hand quadrant of Fig. 8 is replotted (taking account of the projection factor) in terms of projected negative transmission vs. negative exposure. No part of this curve is straight. The foregoing discussion of toe recording has made use of H & D curves derived from time scale exposures, whereas the flashing-lamp records give intensity scale variations of exposure on the negative. In the region of the negative characteristic to which the toe exposures are confined, the difference in shape for the same development between intensity scale and time scale exposures is so small as to be negligible and the conclusions stated above apply substantially to either type of negative modulation.** * The lipht-vnlve ?,imma v;ould be a little higher thin the daylight gamma, but the shapes of the toes would not differ appreciably. **In the Fnx development, daylight time scale strips or gammas of 1.81 and 2.15 show toes which do not differ in shape below a visual density of 0.80. It is not likely that the flashing-lamp gammas would differ more than 10 per cent from the daylight time scale gamma, and it has been mentioned that an intensity scale curve coincides with a daylight time scale curve of the same gamma. There remains the chance that a different negative exposure would be required to give the desired negative density.