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Broadband Noise Re
An Alternative Ambisonics Formulation: Modal Source Strength Matching and the Effect of Spatial Aliasing
126th AES, 7-10 May, Munich, 2009
Ambisonics synthesizes sound fields as a sum over angular (spherical/cylindrical harmonic) modes, resulting in the definition of an isotropically smooth angular resolution. This means, virtual sources are synthesized with outstanding smoothness across all angles of incidence, using discrete loudspeakers that uniformly cover a spherical or cylindrical surface around the listening area. The classical Ambisonics approach models the fields of these discrete loudspeakers in terms of a sampled continuum of plane-waves. More accurately, the contemporary concept of Ambisonics uses a continuous angular distribution of point-sources at finite distance instead, which is considerably easier to imagine. This also improves the accuracy of holophonic sound field synthesis and the analytic description of the sweet spot. The sweet spot is a limited area of faultless synthesis emerging from angular harmonics truncation. Additionally, playback with loudspeakers causes spatial aliasing. In this sense, the contemporary concept allows for a succesive consideration of the major shortcomings of Ambisonics: the limited sweet spot size and spatial aliasing. To elaborate on this, our paper starts with the solution of the nonhomogeneous wave equation for a spherical point-source distribution, and ends with a novel study on spatial aliasing in Ambisonics.