Intelligibility enhancement of casual speech for reverberant environments inspired by clear speech properties

Clear speech has been shown to have an intelligibility advantage over casual speech in noisy and reverberant environments. This work validates spectral and time domain modifications to increase the intelligibility of casual speech in reverberant environments by compensating particular differences between the two speaking styles. To compensate spectral differences, a frequency-domain filtering approach is applied to casual speech. In time domain, two techniques for time-scaling casual speech are explored: (1) uniform time-scaling and (2) pause insertion and phoneme elongation based on loudness and modulation criteria. The effect of the proposed modifications is evaluated through subjective listening tests in two reverberant conditions with reverberation time 0.8s and 2s. The combination of spectral transformation and uniform time-scaling is shown to be the most successful in increasing the intelligibility of casual speech. The evaluation results support the conclusion that modifications inspired by clear speech can be beneficial for the intelligibility enhancement of speech in reverberant environments.