Exaggerated interaural level differences signal that a sound source is near

Evidence

The fourth distance cue in the list is binaural cues, which are essentially directional cues. However, if a source is brought near to a listener from afar in a constant direction, the ITD and ILD cues remain practically the same when the distance r is more than about 1 m. At smaller distances, the ILD cue depends significantly on the distance as well. This is explained by the distance attenuation of sound, which is proportional to the inverse of distance, 1/r, as defined in Equation (2.21). At larger distances, the 1/r-law attenuates sound by practically the same amount for both ears, since the distance between ears is negligible when compared to the distance of the source. With shorter distances, the sound entering the farther ear is attenuated more than the sound entering the closer ear due to the distance difference (Duda and Martens, 1998; Shinn-Cunningham et al., 2000). The ITD values also change, since the sound has to bend around the head causing extra propagation delay, but they do not increase as drastically as the ILD values. Note that this effect is not dependent on frequency, and large ILD values are thus generated at low frequencies too. The exaggerated ILD cue compared to the ITD cue thus suggests a source near to the listener. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1529

Categorization

• DEFINE: Clarifies how ITD and ILD diverge as proximity cues — the head shadow produces distance-dependent ILD for nearby sources.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1529
• XREF: connects to: The head shadows and reflects sound to create level differences between the ears. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1433; Directional hearing rests on interaural time and intensity differences. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 704