Localizing low-frequency sounds in a room and the dominance of interaural level differences

Abstract

In a room-environment study of the duplex theory of sound localization, listeners reported the azimuthal locations of low-frequency sine tones in free field and in three very different rooms. Interaural differences in time (ITD) and level (ILD) were continuously monitored by probe microphones in the listeners' ear canals. As the frequency increased from 250 to 1000 Hz, the correlation of listener responses with the ILD increased while the correlation with the ITD decreased precipitously. The increased importance of the ILD was especially prominent for the least reverberant environments. The decreased importance of the ITD occurred primarily because of interaural phase differences (IPD) that became large (>90 degrees) and consequently weak. The large IPD effect occurred more frequently in the highly reverberant room, and in the less reverberant rooms at 750 and 1000 Hz, where the peak of the IPD distribution occurred well above 90 degrees. The two effects caused the ILD to become more important than the ITD when the frequency was greater than about 500 Hz with only a small dependence on the different rooms. The increased emphasis given to the ILD normally led to more accurate localization. [Work supported by AFOSR grant FA9550-11-1-0101.]