Influence of Deutlichkeit value and reverberation time on improved speech intelligibility in reverberant environments because of steady-state suppression

To improve speech intelligibility in reverberant environments, Arai et al. proposed ‘‘steady-state suppression (SSS)’’ as preprocessing [Arai et al., Acoust. Sci. Technol. 23, 229–232 (2002)]. In this study, a perceptual experiment under artificial reverberant conditions with simulated impulse responses was conducted to elucidate the effect of the Deutlichkeit (D) value and reverberation time (RT) on improvements of speech intelligibility because of SSS. Artificial impulse responses were simulated with white noise multiplied by a decay curve. The advantage of this method is that the simulated impulse responses have mutually similar frequency characteristics; consequently, we can evaluate them using only the D value and RT regardless of their different frequency characteristics. Two parameters, the energy of the impulse response 50 ms from the direct sound and the attenuation rate of the decay curve, were controlled to obtain several impulse responses having certain D value and RT. Results show that SSS improved speech intelligibility in the conditions of low D value, even if RT was long or short. We could also interpret these results as indicating that processing is effective when the original speech intelligibility is less than 60%. [Work supported by JSPS.KAKENHI (16203041).]