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Reduction of spectral artifacts in multichannel downmixing with adaptive phase alignment

: Vilkamo, Juha

Journal of the Audio Engineering Society 62 (2014), Nr.7/8, S.516-526
ISSN: 0004-7554
ISSN: 1549-4950
Fraunhofer IIS ()

Multichannel audio, when reproduced or transmitted over a smaller number of channels, needs to be downmixed. In case the channels contain non-aligned interdependent sounds, the downmixed signal may attain perceivable spectral bias. In the present study a time-frequency domain phase-adaptive downmixing technique is proposed to reduce such spectral effects when necessary. In detail, the technique aligns the phases of the input channel pairs or groups having a high measured normalized inter-channel coherence prior to the downmixing. Simulations and listening tests were conducted to show the conditions in which the proposed method provides benefits with respect to the legacy methods that do not apply phase processing. Computational evaluations showed that the method may be implemented to run in real time with reasonable hardware requirements also with a larger number of input channels, such as with 22.2 surround. The proposed method was adopted in the upcoming MPEG-H 3D Audio coding standard with minor modifications.