The effect of reverberation time on the spatial relationships between interaural differences in a room

The interaural level difference (ILD) and the interaural phase difference (IPD) are the two important physical features whereby a listener can localize a sound source in space. In an anechoic environment, the ILD and IPD measured at the ears are similar functions of angle as the head rotates. But in a room environment these interaural differences behave very differently as the head moves in the room. Experiments reported in 2022 (J. Acoust. Soc. Am. abst. 152 A91) indicated that the ILD and IPD, as measured along a straight line path, appeared to be Hilbert transforms of one another, at least at a sufficiently low frequency such as 250 Hz. For instance, the Hilbert transform of the ITD agreed with the ILD without any adjustable scaling factor. Recent measurements made in various room environments show that the smaller the direct to reverberant ratio, the better the Hilbert transform relationship describes the interaural differences. Shifts of the Hilbert transforms compared to interaural differences along the straight line path, vanish as the reverberation time approaches four seconds. Because functions and their Hilbert transforms are orthogonal, the interaural differences are maximally confusing as a listener moves in a room.