All previously published Ambisonic decoders for irregular loudspeaker layouts have localisation performance which varies significantly by angle around the listener. This contrasts with decoders designed for evenly spaced arrangements of loudspeakers where performance characteristics are isotropic. Furthermore even localisation performance around the listener is desirable for a number of application areas of 5.1 surround sound. New decoder design criteria are presented which aim to reduce this variation in localisation performance. These criteria are added to a multiobjective fitness function, based on auditory localisation theory, which guides a heuristic search algorithm to derive decoder parameter sets for the ITU 5.1 layout. The derived decoders exhibit a significant improvement in localisation performance variation by angle around the 360º sound stage.
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