Arrays of subcritical width rectangular speech bands maintain intelligibility at high intensities

Abstract

Speech intelligibility declines at high intensities for both normally hearing and hearing-impaired listeners, especially at high frequencies (Molis and Summers, 2003). However, it appears that this "rollover" effect can be minimized and intelligibility preserved by reducing speech in high frequency regions to an array of noncontiguous bands having vertical filter slopes (i.e., rectangular bands) and widths substantially narrower than a critical band. Normally hearing listeners were presented with sentences consisting of a 500-Hz lowpass pedestal band, presented at a fixed level of 70 dB, along with a variable-level array of ten 4% bands centered at every other ERBn from 1000 Hz to 8417 Hz. Intelligibility varied by less than 2% when the level of the array was increased from 65 to 95 dB. Most crucially, when within-band noise was added to both the lowpass speech and the subcritical band array, rollover averaging just 3.4% was obtained at a speech level of 95 dB, even when the signal-to-noise ratio was decreased to 0 dB. These results suggest that, in the normally noisy conditions of everyday life, subcritical-width rectangular bandpass filtering may substantially reduce rollover for listeners having substantial high frequency hearing loss.