A spherical microphone array for spatial sound recording

Abstract

The progression of audio from monophonic to the present day 5-channel playback is being driven by the desire to improve the immersion of the listener into the acoustic scene. In the limit, the goal is the reconstruction of the original sound field. This talk describes the decomposition of the sound field into orthogonal components, the so-called spherical harmonics and is directly related to the method of Ambisonics. These components contain all required information to allow a reconstruction of the original sound field. This approach is scalable to any number of loudspeakers and is also backwards compatible to surround sound, stereo and mono playback. One problem is the recording of the orthogonal components. So far only solutions exist that allow the recording of spherical harmonics up to first order. This limits the spatial resolution. This presentation introduces a new microphone that overcomes this limitation. It consists of pressure sensors that are equally distributed on the surface of a rigid sphere. The number of sensors depends on the highest order spherical harmonic to be recorded. A minimum of (n+1)2 sensors is required to record harmonics up to nth order. The sensor signals are then processed to give the desired spherical harmonic outputs.