ILD is primarily caused by which physical effect?

ILD is primarily caused by which physical effect?

• A. Pinna filtering at low frequencies
• B. Differences in arrival time between ears.
• C. Spectral cues from the outer ear.
• D. Head shadowing that attenuates high-frequency sound.

Answer: (D)

Interaural level differences come from the head shadow effect. When a sound arrives from one side, the head blocks and absorbs some energy before it reaches the far ear, creating a difference in sound level between the two ears. This shadowing effect is highly frequency-dependent: high-frequency sounds have short wavelengths that don’t diffract well around the head, so the far ear is noticeably attenuated and a large ILD is produced. At low frequencies, wavelengths are long enough to wrap around the head more easily, so the level difference between ears is small and timing differences (ITD) become more informative for localization. Pinna filtering and spectral cues from the outer ear affect how we identify elevation, front–back, and the spectral shape of sounds, but they don’t primarily generate the interaural level difference. So the main physical cause of ILD is head shadowing that attenuates high-frequency sound.

Interaural level differences come from the head shadow effect. When a sound arrives from one side, the head blocks and absorbs some energy before it reaches the far ear, creating a difference in sound level between the two ears. This shadowing effect is highly frequency-dependent: high-frequency sounds have short wavelengths that don’t diffract well around the head, so the far ear is noticeably attenuated and a large ILD is produced. At low frequencies, wavelengths are long enough to wrap around the head more easily, so the level difference between ears is small and timing differences (ITD) become more informative for localization. Pinna filtering and spectral cues from the outer ear affect how we identify elevation, front–back, and the spectral shape of sounds, but they don’t primarily generate the interaural level difference. So the main physical cause of ILD is head shadowing that attenuates high-frequency sound.