Loudness of speech pronounced by a visible or hidden speaker located at several distances
Résumé
The at-ear pressure level of a sound decreases as the distance between the source and the listener increases. However, a form of loudness constancy with sound source distance has been revealed under certain experimental conditions by several studies in the literature. In the present study, listeners were instructed to evaluate both the loudness "at the ears" (the extent to which the sound has been heard loud) and the loudness "at the source" (the extent to which the sound has been emitted loud) of speech as a function of the source distance. The speech signals under test consisted in disyllabic french words pronounced with different vocal efforts by a speaker located at several distances from the listening point. The speaker could be either visible or hidden, providing or not the listeners with visual information about his relative distance and his vocal effort. The experiment took place in both anechoic and reverberant virtual environments, providing or not the listeners with absolute auditory cues to the speaker's distance and acoustic power. The results show a robust constancy with distance for the estimates focusing on the loudness "at the source", whereas the loudness "at the ears" was clearly following the at-ear sound pressure variations induced by distance. These results differ to some extent from those previously observed for white noises, which do not provide intrinsic information about their source power. Moreover, the loudness functions obtained when the listeners estimated the loudness "at the ears" for speech were similar to those obtained for noises in a previous experiment. This result somehow differs from those obtained in the literature where the overall loudness of noises or speech was evaluated without specifically focusing the listener's attention on the loudness "at the ears".
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