Preprocessing of an Already Noisy Speech Signal for Intelligibility Enhancement

Abstract

A preprocessing technique which enhances speech intelligibility in noise when the noise enters after preprocessing has been described recently [I. B. Thomas and R. J. Niederjohn, “The Intelligibility of Filtered-Clipped Speech in Noise,” J. Audio Eng. Soc. 18, 299–303, (1970)]. The preprocessing technique involves high-pass filtering (cutoff 1100 Hz, slope 12 dB/oct) and infinite amplitude clipping. In the present experiments, we have determined the intelligibility of speech which has been passed through this same system but in which noise is added prior to filtering and clipping. Ten subjects took part; all signals were presented binaurally in phase through headphones. The noise signal was white noise, bandlimited from 250 to 6800 Hz. Intelligibility scores (percent) for Harvard PB words at signal-to-noise ratios of 0, 5, and 10 dB (measured at the microphone) were as follows: for unmodified speech, 40, 65, and 80; for filtered-clipped speech, 47, 82, and 96; for filtered-clipped-differentiated speech, 47, 74, and 95. [Work supported by NIH.]