Speech intelligibility in noise: Relative contribution of speech elements above and below the noise level

In a previous study [R. Drullman, J. Acoust. Soc. Am. 97, 585–592 (1995)], the relative contribution of temporal modulations and fine structure to sentence intelligibility was investigated. This Letter reports additional listening experiments to assess in more detail the effect of masking noise on the peaks and troughs of the speech signal. For this purpose, the signal structure of each 1/4-oct band in a 24-band filterbank (100–6400 Hz) was altered by manipulating the distribution of speech and noise over the sentences. Results for 12 normal-hearing subjects indicate that removing noise from the peaks has no effect on intelligibility; removing the speech signal from the noisy troughs, however, yields a 2-dB increase of the speech-reception threshold. So, it appears that, even below the noise level, weak speech elements do contribute to intelligibility.