Effects of inter-word pauses on speech intelligibility under long-path echo conditions

Long-path echo is a salient factor that causes the degradation of the intelligibility of speech transmitted through a wide area outdoor environment or a very large indoor space using public-address systems. To robustly transmit speech information under such conditions, it is important to overcome this effect by controlling the characteristics of speech sounds. In this study, we consider the effects of inserting pauses between the words of a sentence. We performed word intelligibility tests using a series of four continuous words, called a quadruplet. Various pause lengths and long-path echo patterns were applied to the quadruplet. The results of the experiments demonstrate that word intelligibility under a long-path echo is significantly improved by the insertion of pauses between the words. Intelligibility can approach the same levels observed in the absence of echoes for a pause length of approximately 200 ms, which is almost the same as the length of 1-mora for the words used in the experiments. Moreover, this 200 ms pause is known to be sufficient to improve speech recognition in older adults. These results suggest that inter-word pauses of a length of approximately 1-mora can generally enhance the robustness of speech communication systems when used under a severe environment.