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TECHNIC OP RECORDING CONTROL
411
mately 40 sensation units, would be totally inadequate. However, there are some features which limit the practical use of this whole range, other than those that reside in the recording system: First, the average noise in a theatre from the venti
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0 16 32 64 128 256 512 W24 2046 4096 8192 16354 FREQUENCY O.V. 300400500600 700 8009001000 U00 1200 1300 1400 PITCH UNITS.
FIGURE 2
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lators, audience, etc., is seldom less than 30 sensation units above minimum audibility, and is frequently as much as 40. It is, therefore, useless to reproduce in the theatre any sounds less than 40 sensation units above minimum audibility, as they would become lost in this noise. Second, the upper 30 or more sensation units represent sound intensities of the magnitudes encountered from the firing of big guns, large explosions and other uncomfortably loud sounds.
Therefore, except for the few isolated cases, where records are being made of such explosions, the practical useful ranging has been reduced by 70 sensation units, and there remains only 30 to 50 to be accommodated ordinarily. The Western Electric recording system can easily accommodate 30, and when properly maintained and operated, can accommodate 40. When it is considered that the difference in loudness, between a stage whisper and a very loud shout is about 30 sensation units, it will be seen that the limits of the system do not ordinarily handicap recording.
In the terms of the movies, Fig. 3 is a close-up of the curve shown in Fig. 2, with four additional curves added. These four curves represent the lines of constant loudness of 20, 40, 60 and