Real-time sound pressure interpolation around a rigid sphere using IIR filters based on spherical harmonic expansion

Abstract

Sound pressure interpolation is important for applications such as Active Noise Control (ANC) with virtual sensing. However, many interpolation methods, developed in the frequency domains in free fields, cannot be directly used for real-time processing with consideration of head reflections, such as ANC headrests. To overcome this problem, we propose a low-delay interpolation method using IIR filters for each order of spherical harmonic expansion. These IIR filter coefficients are derived from rigid-sphere transfer functions in the z-plane. A computer simulation showed that the proposed method can predict the sound pressure on a rigid sphere using an open sphere microphone array.