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J. A. MAURER
[J. vS. M. p. E.
This has been done in Fig. 4, where each curve corresponds to a given negative density and shows by its rise and fall how the sound output varies with the depth to which it is printed. Naturally with short printer exposures the output is low because of the low density of the print. As the exposure is increased the sound output increases up to a certain point, after which it falls off again because the clear side of the track begins to be fogged.
The curves of Fig. 4 have been plotted in decibels because this enables us to interpret them directly in terms of the steps on the gain control of a theater installation. The zero level is the same as the
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DENSITY OP PRINT SOUND TRACK
2.0
FIG. 4. Dependence of sound output on negative and print density. (Dotted curves are experimental.)
100 per cent line of Fig. 2. It will be remembered that the smallest step on the gain control is two decibels, this being the smallest noticeable difference in level. Then from Fig. 4 it appears that prints made from negatives of density 1.0 or greater are all within one step of the same level. As far as sound output is concerned there is no need of working for greater densities in the negative.
A point worth noting is that a level of minus one decibel on this scale is the highest obtainable in practice because positive film will always fog in the developer to a density of at least 0.05 regardless of whether it has received any exposure or not. The 11 per cent loss caused by this amount of fog amounts to almost exactly one decibel.