Novel findings concerning intelligibility of bandpass speech.

Abstract

Very high intelligibility was found for a number of narrow-band filtering conditions. Four hundred listeners (20 groups of 20 subjects) were presented with bandpass filtered CTD sentences (‘‘everyday speech’’) and monosyllabic words. Separate groups received center frequencies of 370, 530, 750, 1100, 1500, 2100, 3000, 4200, or 6000 Hz at 70 dBA SPL. In experiment 1, intelligibility of single 1/3-octave bands with steep filter slopes (96 dB/oct) averaged more than 95% for sentences centered at 1100, 1500, and 2100 Hz, and more than 50% for monosyllabic words centered at 1500 and 2100 Hz. Experiment 2 used the same center frequencies with extremely narrow bands (slopes of 115 dB/oct intersecting at the center frequency)−intelligibility remained relatively high for most bands, with greatest intelligibility at 1500 Hz (77% for sentences, 18% for words). In experiment 3, 1/3-octave bands (96 dB/oct) centered at 370 and 6000 Hz were presented simultaneously either diotically or dichotically (when presented separately in experiment 1, intelligibility of these bands did not differ significantly, and averaged 23% for sentences and 3% for monosyllabic words). When the bands were combined, diotic and dichotic presentations were equivalent. Intelligibility rose to an average of 77% for sentences and 34% for words. [Work supported by NIH Grant No. DC00208.]