Modulation enhancement of speech as a preprocessing for reverberant chambers with the hearing-impaired

Abstract

In this paper we report on a method for reducing the degradation of speech intelligibility in public halls caused severe reverberation. Hall reverberation makes speech more difficult to understand, particularly for the hearing-impaired. Our method involves processing the speech audio signal between a microphone and a loudspeaker that radiates the speech into the room. As there is a strong correlation between the modulation spectrum and the intelligibility of speech, we filtered the speech in the modulation frequency domain. Using several modulation filters, we conducted perceptual experiments with hearing-impaired subjects and asked their preference in a church. The experiments indicate that enhancing the modulation frequencies between 2 and 8 Hz improves intelligibility in reverberant environments. The four hearing-impaired subjects rated the processed speech easier to hear than the unprocessed speech.