Efficient Out of Head Localization System for Mobile Applications

Headphone reproduction of stereo sources often gives in-the-head-localization. One possible solution to this problem is to give directional filtering and room response to the headphone reproduction system. Conventional out of head localization (OHL) schemes consist usually of a tapped delay line to simulate the direct signal path and early room reflections. Each of the taps must be filtered by a pair of HRTF, which leads to a very high processing cost. Our study is based on the fact that spatial impression (SI) can increase the effects of OHL. Our research is to generate the maximum SI with a minimum cost. Through subjective listening tests, the degree of SI was found to be the greatest for reflections within 15 to 30msec time frame from the direct sound and it is greatest for those in opposite direction to the listener’s ears. Based on the test results, we propose an efficient OHL system. In the proposed system, multiple reflections are replaced by a pair of reflections, and HRTF filtering required to simulate directivity of the reflections is implemented using a set of first order IIR shelving filters. According to the subjective tests, we show that the proposed system efficiently creates OHL with a small computational figure, and its performance is comparable to the conventional scheme of high complexity.