Binaural Speech Intelligibility in a Real Elementary Classroom

Since the fundamental phases of the learning process take place in elementary classrooms, it is necessary to guarantee a proper acoustic environment for the listening activity to children immersed in them. In this framework, speech intelligibility is especially important. In order to better understand and objectively quantify the effect of background noise and reverberation on speech intelligibility various models have been developed. Here, a binaural speech intelligibility model (BSIM) is investigated for speech intelligibility predictions in a real classroom considering the effect of talker-to-listener distance and binaural unmasking due to the spatial separation of noise and speech source. BSIM predictions are compared to the well-established room acoustic measures as reverberation time (T30), clarity or definition. Objective acoustical measurements were carried out in one Italian primary school classroom before (T30= 1.43s±0.03 s) and after (T30= 0.45±0.02 s) the acoustical treatment. Speech reception thresholds (SRTs) corresponding to signal-to-noise ratio yielding 80% of speech intelligibility will be obtained through the BSIM simulations using the measured binaural room impulse responses (BRIRs). A focus on the effect of different speech and noise source spatial positions on the SRT values will aim to show the importance of a model able to deal with the binaural aspects of the auditory system. In particular, it will be observed how the position of the noise source influences speech intelligibility when the target speech source lies always in the same position.

Measurement and Prediction of Binaural-Temporal Integration of Speech Reflections

For speech intelligibility in rooms, the temporal integration of speech reflections is typically modeled by separating the room impulse response (RIR) into an early (assumed beneficial for speech intelligibility) and a late part (assumed detrimental). This concept was challenged in this study by employing binaural RIRs with systematically varied interaural phase differences (IPDs) and amplitude of the direct sound and a variable number of reflections delayed by up to 200 ms. Speech recognition thresholds in stationary noise were measured in normal-hearing listeners for 86 conditions. The data showed that direct sound and one or several early speech reflections could be perfectly integrated when they had the same IPD. Early reflections with the same IPD as the noise (but not as the direct sound) could not be perfectly integrated with the direct sound. All conditions in which the dominant speech information was within the early RIR components could be well predicted by a binaural speech intelligibility model using classic early/late separation. In contrast, when amplitude or IPD favored late RIR components, listeners appeared to be capable of focusing on these components rather than on the precedent direct sound. This could not be modeled by an early/late separation window but required a temporal integration window that can be flexibly shifted along the RIR.