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The University of Southampton

Animation 10

Cross-Talk Cancellation: frequency domain, KEMAR model, four loudspeakers (view of the acoustic field)

Cross-talk cancellation for a 4x4 system

In this system we do not attempt to reconstruct the sound pressure at the eardrum exactly. It has been shown that the main advantage of such an arrangement is that the rate of change of the interaural cross-correlation (IACC) function with respect to head rotations in a four channel system, with loudspeaker also placed behind the listener, can be reproduced. Our goal in this case is to reconstruct the accurate pair of HRTFs at the blocked ear canal when the head is rotated at angles of ±50. In this animation we demonstrate the operation of the cross talk cancellation by reproducing “1” at ear no. 1 and “0” at all the others (this is achieved by multiplying the vector [1 0 0 0]T with the cross-talk cancellation matrix H). We can notice the effect of the cross talk cancellation on the robustness of head rotations: the zero pressure in the right side is maintained when the head is rotated, and on the left side a rapid change between “0” and “1” is achieved. Two conclusions can be reached from this example: the use of four ears for calculation of filters for a single listener proves very robust to head rotations and can provide important cues for front and back discrimination. Secondly, the 'sweet spot' is reduced in comparison to the 2x2 system presented in the previous example. If the head is moved forward or backward the cross-talk cancellation effect disappears.

The sound field in the vicinity of KEMAR is presented with the same filtered signals that were used to calculate the desired signals and the response on the surface of KEMAR. The animation shows the amplitude of the resultant pressure at discrete frequencies. Since the desired signals include two points to each ear: one is moved slightly towards the frontal hemisphere, and the other towards the rear, the sound pressure varies rapidly in the left ear of the dummy-head when it is rotated slightly, whereas the sound pressure in the vicinity of its right ear is maintained under the conditions of the cross-talk cancellation with zero pressure. The complexity of the sound field and the effects of the interference between the waves are clearly shown at high frequencies.

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