Interaural level differences only emerge at frequencies above roughly 400 Hz.

Evidence

Scattering is a frequency-dependent phenomenon, since wavefronts arriving from distant sources - plane waves - produce ILD only where the head is large enough compared to the wavelength to affect the acoustic field around it. As can be seen from Figure 12.7, the level of the HRTF magnitude responses is constant for frequencies below about 400 Hz, and the dependence on the azimuth angle increases for higher frequencies, reaching more than 20 dB at frequencies above 4 kHz. Therefore, it is a natural consequence that the ILD is a strong 0. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1434

Categorization

• QUESTION: Passage cuts off mid-sentence, obscuring the stated consequence about low-frequency localization.
• XREF: connects to: Interaural time differences are only usable below about 1500 Hz; Interaural level differences grow with frequency and side placement — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1455; Head shadowing gives roughly 6 dB interaural amplitude difference near 1.85 kHz (+2 more)

Broader Connections

• Interaural time differences are only usable below about 1500 Hz #qualifies (0.85)
• Interaural level differences grow with frequency and side placement #corroborates (0.80) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1455
• Head shadowing gives roughly 6 dB interaural amplitude difference near 1.85 kHz #exemplifies (0.78)
• Directional hearing rests on interaural time and intensity differences. #expands (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 704
• Interaural level differences alone can shift the perceived position of a sound source #corroborates (0.72) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 3357