Handling Spatial Aliasing in Spherical Array Applications

Spherical microphone arrays are an attractive solution for many audio applications where flexible beamforming in all directions is desired. However, as with all discretely sampled array systems, spatial aliasing puts a constraint on the upper operating frequency range and therefore limits some potential applications. Simply increasing the number of sensors to overcome the effect of spatial aliasing is effective but can be expensive, especially if very high quality microphones elements are used. This paper reviews the origin of spatial aliasing for spherical arrays based on modal beamforming and investigates alternative approaches to mitigate the spatial aliasing problem. The alternative approaches are based on: spatial anti-aliasing filters, exploiting the natural diffraction of the spherical baffle and compromising the directivity at higher frequencies. All approaches are practical and can be implemented without increasing the system cost significantly.