Prediction of Speech Intelligibility at High Noise Levels
J. M. Pickett, Irwin W. Pollack · The Journal of the Acoustical Society of America · 1957
Word articulation tests were conducted with three noise spectra (spectral slopes of −12, 0, and +6 db per octave) and with two speech spectra (spectral tilt of 0 to +6 db per octave) with noise levels up to 130 db SPL. Loss of intelligibility was observed at higher noise levels for all spectral conditions examined. The effective change in the speech-to-noise ratio (S/N)e defines the effect of high noise levels upon intelligibility. This quantity is that change in the S/N ratio which, at moderate listening levels, produces the equivalent change in intelligibility observed at high noise levels. To a first approximation, (S/N)e is primarily dependent upon the over-all noise level. For example, as the over-all noise level is increased from 90 to 125 db SPL, (S/N)e increases to 4.5 db (averaged over spectra and averaged over S/N ratio). However, (S/N)e is not invariant with spectra and S/N ratio. (S/N)e is generally higher at more favorable S/N ratios, and it is also somewhat lower when speech and noise spectra are parallel than when divergent. The use of (S/N)e for predicting intelligibility at high noise levels is compared with procedures suggested by French and Steinberg and by Beranek.