Rotation Calibration of Rigid Spherical Microphone Arrays for Multi-perspective 6DoF Audio Recordings

The preferred approach for multi-perspective six-degrees-of-freedom (6DoF) audio involves using multiple rigid spherical microphone arrays (RSMA) that can capture higher-order Ambisonics. RSMAs are spherically symmetric and allow the calculation of the local decomposition of sound fields over spherical harmonic functions. When multiple such arrays are used, multiple scattering occurs that can be equalized via methods that rely on multipole expansions if the positions of the arrays are known and the coordinate frames of arrays are aligned. In a practical scenario, however, when such a set of arrays are placed in location, their positions will not be exact and their coordinate frames will not be fully aligned. This paper is concerned with the correction of rotational mismatches in azimuth angles of individual RSMAs. The effects of such misalignment on the calculation of the local multipole expansion of the sound field are numerically explored. A rotation calibration approach that depends on non-linear optimisation is proposed. Numerical evaluations of different scenarios are presented.