Influence of the direction of a single reflection on speech intelligibility

Abstract

Speech intelligibility in a complex environment such as a room is affected not only by competing sound sources but also by reflections off walls, the ceiling, or the floor. In this context, the benefit of early reflections for intelligibility in rooms has been demonstrated principally. In which way the auditory system achieves this improvement is still a matter of discussion. Therefore, a speech comprehensibility test was performed in a simulated scenario. Each stimulus consists of a speech target sound that emanates from a 45° azimuth direction and competes with a noise source at −45° azimuth. Both are in the horizontal plane. The speech target is accompanied by a single reflection adjusted in time-delay and level relative to the primary sound to be beneficial for intelligibility [e.g., Nabelek and Robinette, J. Acoust. Soc. Am. 63, 187–194 (1978)]. During the tests, the variable under investigation was the direction of the reflection. Speech comprehensibility was measured with an open response paradigm utilizing meaningless one-syllable words as speech material. The direction-dependent results indicate an interaction of influences in accordance with earlier findings.