Three-dimensional sound recording using directional beams

The recording of three-dimensional spatial audio is typically carried out using microphone arrays that produce higher-order B-format responses, which are defined by spherical harmonics. Spherical harmonics provide a compact, orthonormal representation of the sound field, but can be intuitively challenging for general users because they do not have a direction, as opposed to typical microphones used in the audio industry. Furthermore, spherical microphone arrays typically use microphone angles based on Platonic solids which do not have intuitive directions such as front, rear, left, right, up, and down. This paper considers the use of sets of directional beams that have orthonormal properties in a similar manner to spherical harmonics. Sets of angles that have intuitive directions are used, and a method of approximating orthonormal beams is developed. The approach can also be applied to angles obtained from Platonic solids. Finally, a prototype microphone array that implements the directional recording format is described.