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Inverse filtering for virtual acoustic imaging systems

By Timoleon Papadopoulos


The research topic of this thesis is the use of inverse filtering for the design and<br/>implementation of two-channel virtual acoustic imaging systems that utilise<br/>loudspeakers. The basic objective of such systems is to invert the electroacoustic plant<br/>between the input to the loudspeakers and the output at the listener’s ears and hence<br/>make it possible for a pair of binaural signals to be locally reproduced at the position<br/>of the listener’s ears. As a starting point for the research presented, a previously<br/>introduced type of inverse filtering design is considered in which the inverse is<br/>implemented with FIR filters. The basic formulation of this design is described and a<br/>number of innovative points regarding its implementation are made. An experimental<br/>procedure is then formulated for the evaluation of the effectiveness of this inverse<br/>filtering design that is based on objective measurements of the inversion process.<br/>Unlike previously employed methods that are based on computer simulations or<br/>subjective experiments, the introduced experimental procedure is shown to be very<br/>efficient in isolating and exactly quantifying the effect on the accuracy of the<br/>inversion of a number of errors and approximations typically present in the<br/>implementation. A detailed evaluation is thus presented of the inverse filtering design<br/>at hand in realistic conditions of implementation. Subsequently, a novel method for<br/>the off-line implementation of the inverse filtering is presented that utilises recursive<br/>filters of lower order. In this method, the responses of the inverse filters are<br/>decomposed into two parts, one realisable in forward time and one in backward time.<br/>The effectiveness of this new method for the implementation of the inverse is tested<br/>and compared with a small selection of the objective evaluation results described<br/>above. Finally, an algorithm for the on-line implementation of the forward-backward<br/>inverse filtering is proposed and its computational cost is compared with the currently<br/>available frequency-domain block-processing filtering algorithms

Topics: QC
Year: 2006
OAI identifier:
Provided by: e-Prints Soton
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