Investigation of the optimum acoustical conditions for speech using auralization

Abstract

Speech intelligibility is mainly affected by reverberation and by signal-to-noise level difference, the difference between the speech-signal and background-noise levels at a receiver. An important question for the design of rooms for speech (e.g., classrooms) is, what are the optimal values of these factors? This question has been studied experimentally and theoretically. Experimental studies found zero optimal reverberation time, but theoretical predictions found nonzero reverberation times. These contradictory results are partly caused by the different ways of accounting for background noise. Background noise sources and their locations inside the room are the most detrimental factors in speech intelligibility. However, noise levels also interact with reverberation in rooms. In this project, two major room-acoustical factors for speech intelligibility were controlled using speech and noise sources of known relative output levels located in a virtual room with known reverberation. Speech intelligibility test signals were played in the virtual room and auralized for listeners. The Modified Rhyme Test (MRT) and babble noise were used to measure subjective speech intelligibility quality. Optimal reverberation times, and the optimal values of other speech intelligibility metrics, for normal-hearing people and for hard-of-hearing people, were identified and compared.