The impact of early reflections on binaural cues

Boris Gourévitch and I have just published a paper in ecological acoustics:

Gourévitch B and Brette R (2012). The impact of early reflections on binaural cues. JASA 132(1):9-27.

This is a rather technical paper in which we investigate how binaural cues (ITDs, ILDs) are modified in an ecological environment in which there are reflections. Indeed most sound localization studies use HRTFs recorded in anechoic conditions, but apart perhaps from flying animals, anechoic conditions are highly unecological. That is, even in free field, there is always at least a ground on which sounds waves reflect. In this paper, we focus on early reflections. In the introduction, we motivate this choice by the fact that the precedence effect (perceptual suppression of echoes) only acts when echoes arrive after a few ms, and therefore early reflections should not be suppressed. Another, perhaps simpler, argument is that in a narrow frequency band, a sound will always interfere with its echo when the echo arrives less than a couple of periods after the direct sound. Therefore, early reflections produce interferences, seen in the binaural cues. An important point is that these are deterministic effects, not variability. In the paper, we analyze these effects quantitatively with models (rigid spheres and sophisticated models of sound absorption by the ground). One implication is that in ecological environments and even with a single sound source and in the absence of noise, there may be very large interaural time differences, which carry spatial information.


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