Effect of spatial separation of sources on speech intelligibility in an automotive environment

Abstract

Speech intelligibility has been shown to be enhanced when the target speech source is spatially separated from the interferer, which is related to the spatial unmasking phenomenon. However, this issue has not been studied in the small acoustical space of an automobile. This study, thus, examines the effect of spatial separation of sources on the speech reception threshold (SRT) in an automobile, and compared with the results in a weak-reflective listening room. The target was always presented at the front-passenger seat, and the interferer was presented at the front-passenger seat, right-back seat, mid-back seat, and left-back seat in sequence. The stimuli were synthesized using convolution with binaural room impulse responses measured on a dummy head in driver seat under different interferer locations. Sentence SRTs in Mandarin Chinese were measured via headphones virtually in an automobile and a listening room. Accordingly, the spatial release from masking (SRM) was obtained based on the SRT result. Results show that the SRM in automobile is always smaller than that in listening room, because the early reflections and seat-back occlusions cannot only obscure the binaural cues related to the source localization such as the interaural-time-difference and interaural-level-difference, but also influence the target-to-interferer ratio.