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Icsa 2017
Sep 7th to 10th, 2017
Graz, Austria

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ICSA 2017 4th International Conferenceon Spatial Audio | September 7th to 10th, 2017, Graz, Austria #vdticsa

Ambisonic microphone encoding with covariance constraint

Typically, encoding the signals of Ambisonic microphone arrays is done by either (i) a least-squares approach based on the measured or modelled directional array responses, or (ii) the theoretical frequency-dependent order-weights of the spherical harmonics decomposed microphone signals. In either case, the high frequencies are not mapped with the correct magnitude. They are under- represented when using least-squares encoding above the spatial aliasing frequency, or over-emphasized when the encoding is based on the reciprocal order-weights. To enforce a correct high-frequency magnitude, this paper proposes an additional magnitude constraint for the least-squares solution. Moreover, the addition of quadratic constraints permits further improvement: By constraining all components of the covariance matrix, not just its trace, the encoding achieves a superior representation of diffuse fields, in addition to the timbral improvement.