Enhancement of spatial sound recordings by adding virtual microphones to spherical microphone arrays

Spherical microphone arrays mounted on a rigid spherical baffle effectively capture acoustic environments for their reconstruction by sensing the space in all directions. The array signals are further encoded for their scalable processing using the spherical Fourier transform. Recent spatial sound applications are demanding arrays with a large number of microphones. However, physically increasing the spatial resolution of available arrays is not always feasible. In environments such as conference rooms or concert halls the source positions are often confined to a small region of space. When prior knowledge about source positions is assumed, the pressure generated at any point on the baffle can be estimated with a physical model of the rigid sphere. In this paper, the rigid sphere model is used to define a surface pressure variation function that relates the pressure at two arbitrary points on the baffle. Based on this function, a spatial resolution enhancement method for spherical arrays is proposed, which aims to add virtual microphones to the array by synthesizing recording of signals at positions without microphones. The proposal constitutes a preprocessing stage intended to be applied before array signal encoding. Numerical experiments show that the enhancement of spatial resolution is possible all over the sphere if the number of real microphones is sufficiently large.