Spatial Audio Processing: MPEG Surround and Other Applications

3.4 Spatial hearing in rooms

3.4.1 Source localization in the presence of reflections: the precedence effect

Usually, the direct sound of a source reaches the ears earlier than the reflections of the same sound because the indirect path associated with a reflection is longer than the direct path from the source to the ears. The precedence effect describes a number of phenomena related to the auditory system's ability to resolve the direction of a source in the presence of one or more reflections by favoring the ‘first wavefront’ over successively arriving reflections. That is, the directional perception of reflections arriving within a few milliseconds after the direct sound is suppressed and the direct sound and these reflections are ‘fused’ into one single auditory object at the direction of the direct sound. Extensive reviews of the precedence effect have been given by Zurek [291], Blauert [26], and Litovsky et al. [183].

A typical precedence effect experiment is illustrated in Figure 3.11. The signals given to two loudspeakers are illustrated in Figure 3.11(a). The signal x₁ contains pulses repeating at regular intervals τ_p. The same pulse train is contained in signal x₂, but slightly delayed by τ_e. Typical values for τ_p and τ_e are 400 and 5 ms, respectively. When listening to these signals over a standard stereo setup a listener will perceive only one auditory object at the position of the loudspeaker which emits x₁.

Figure 3.12 illustrates the three phases of the precedence ...