Interaural Level Difference
In binaural hearing the interaural level difference has an impact on lateralization throughout the frequency spectrum. Experimental results show that Interaural Level Differences of 15-20 dB will completely move an image to one side. Interaural Level Differences above 8-10 dB increased the width of the image. In general, Interaural Level Differences have the most effect around 2 kHz with decreasing sensitivity for lower and higher frequencies.
Interaural intensity differences have more complicated variations with frequency than interaural time delays, due to the influence of the pinna, the shape of the head, and their variation across listeners.
- Head and pinna diffraction attenuates sound at far ear, while boosting the sound at near ear.
- Greatest for high frequency sounds.
- Most pronounced for frequencies>1500Hz.
- About 20 dB at 6000Hz, almost 0dB at 200Hz.
- A perfectly coherent ~diotic! noise is normally perceived as a compact image near the centre of the head. Introducing a small interaural level difference moves the image to the left or right but retains the compact character if this difference in level is less than about 8 dB. By contrast, a binaurally uncorrelated noise forms a fuzzy image that fills the head.