Projector Noise Levels
G. E. Whitney, M. T. Buckelew, J. F. McGrane, Morton L. Baron · Journal of the SMPTE · 1959
Analytical and empirical tests have been made to determine optimum noise levels of photographic projectors. It is shown that to achieve 96% “intelligibility” (per cent of sentences understood) the projector should have an articulation index (a quantity related complexly to noise and frequency) greater than 0.4. The index is simple to determine when the projector noise spectrum parallels the spectrum for ordinary speech, i.e., when it peaks near 500 cycles/sec. Measurement of the index is more difficult when the spectra are nonparallel.