Maintaining speech intelligibility at 100 dB using arrays of subcritical width rectangular bands

Abstract

The Speech Intelligibility Index employs 16 contiguous 1/3-octave bands that sample the importance of frequencies across the speech spectrum. The present study employed the same Center Frequencies (CFs) using “Everyday Speech” sentences, but reduced the original 1/3-octaves having 26% bandwidths to 4% effectively rectangular bands (4800 dB/octave slopes). The resulting array of 16 subcritical-width bands had an intelligibility of 96% when heard at 60 dB despite having less than 16% of the 1/3-octave bandwidths. But, increasing the amplitude to 100 dB produced a decrease in intelligibility (“rollover”) to 86%. In a parallel experiment, when the sixteen bands had a bandwidth of 40 Hz for each of their CFs, the intelligibility was 95% at 60 dB and decreased to 91% at 100 dB. But when a “chimera” or hybrid was created with a width of 40 Hz for all CFs from 0.25 kHz to 1 kHz, and a width of 4% for CFs from 1 kHz (bandwidth of 40 Hz) to 8 kHz (bandwidth of 320 Hz), then intelligibility was 99% at 60 dB, and 97% at 100 dB. Hybrids of this type may be of use in hearing aid design. [Research supported by NIH.]