Speech Intelligibility In A Stationary Multipath Channel.

Abstract

The reception of speech transmitted through an acoustic channel such as the ocean is limited by multipath 'time-smearing.' The purpose of this study was to obtain a quantitative measure of the effects of such time-smearing on speech intelligibility. A linear, time-invariant channel was used as a model of the ocean. The impulse response of this channel was a sample of band-limited Gaussian noise. Using Fast Fourier Transform techniques, words of the Modified Rhyme Test were convolved with, or smeared in the time domain, by this channel impulse response. The intelligibility of these 'smeared' words was measured as a function of the impulse response duration, T. Intelligibility decreased monotonically to about 75 percent as T increased to 200 millesconds. Further increase in T did not significantly lower intelligibility. Distortions in time evaluated herein did not impose serious limitations to the reception of short words. However, a detailed analysis of consonantal errors revealed that sounds occurring in the middle of a word are much harder to hear correctly than are sounds at the beginning or end of an utterance. We conclude that time-smearing will more seriously interfere with the intelligibility of connected or conversational speech. (Author)