Medizinische Physik

Effects of spatial and temporal integration of a single early reflection on speech intelligibility

Anna Warzybok, Jan Rennies, Thomas Brand, Simon Doclo, Birger Kollmeier, J. Acoust. Soc. Am. 133(1):269-282, January 2013

In order to study the interaction between the intelligibility advantage in rooms due to the presence of early reflections and due to binaural unmasking, a series of speech reception threshold experiments was performed employing a single reflection of the frontal target speech source as a function of its delay ranging from 0 to 200 ms. The direction of the reflection and the spatial characteristic of the interfering noise (diotic, diffuse, or laterally localized) were varied in the experiments. For the frontal reflection, full temporal integration was observed for all three noise types up to a delay of at least 25 ms followed by gradual intelligibility decay at longer delays. At 200 ms delay the reflection introduced additional intelligibility deterioration. For short delays, intelligibility was not reduced when the reflection was spatially separated from the direct sound in the diffuse and lateral noise conditions. A release from the deterioration effect at 200 ms delay was found for all spatially separated reflections. The suppression of a detrimental reflection was symmetrical in diffuse noise, but azimuth-dependent in lateral noise. This indicates an interaction of spatial and temporal processing of speech reflections which challenges existing binaural speech intelligibility models.

Acknowledgements: This study was supported by the Ministry of Science and Culture of Lower Saxony, Germany (PhD program "Hearing," Fraunhofer Project Group Hearing, Speech and Audio Technology), and the Deutsche Forschungsgemeinschaft (SFB/TRR 31). Three anonymous reviewers are kindly acknowledged for all their constructive remarks on a previous version of this manuscript, which have improved its quality considerably.

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