Directional Masking Coders for Multichannel Subband Audio Data Compression Systems
When monophonic subband audio data compression systems are used with multichannel sound reproduction systems, codec error artifacts are liable to severe directional unmasking, especially if followed by a matrix processing stage. Methods are described of reducing this problem by adopting new subband coding strategies that align the direction of coding errors with that of the wanted signal, and two algorithms to implement such directional alignment are described. An additional analysis shows that residual directionally unmasked error artifacts can be reduced by up to 6dB by a careful choice of an orthogonal or unitary post-codec matrix, rather than the highly non-: orthogonal matrices used in some proposals for HDTV sound.
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