The effect of permutations of time samples in the speech waveform on intelligibility

This paper describes the effect of two types of temporal permutations of the speech waveform on speech intelligibility. Using an overlap-add procedure with triangular-shaped windows for frame lengths of 1/8 to 2048 ms, the temporal order of the speech samples within each frame was subjected to either of two types of permutations: time-reversal or randomization. For both permutations, speech intelligibility tests expectantly show 100% intelligibility for the very short frame lengths containing only a few speech samples. Intelligibility drops to essentially zero toward longer frame lengths of around 1 ms. Interestingly, only for the reverse condition, intelligibility recovers to essentially 100% for frame lengths in the 4-32 ms range, dropping again to zero for frame lengths exceeding about 100 ms. Tests for the Japanese and the English language show essentially similar results. The data are interpreted along the lines of a previous paper by Kazama and the present authors [J. Acoust. Soc. Am. 127(3), 1432-1439 (2010)]. As in that previous paper, the loss of temporal envelope correlation shows a pattern very similar to that of the intelligibility data, illustrating again the importance of the preservation of narrow-band envelopes for speech intelligibility.