Compression of Higher-Order Ambisonic Signals using Directional Audio Coding

Delivering high-quality spatial audio in the Ambisonics format requires extensive data bandwidth, which may render it inaccessible for many low-bandwidth applications. Existing widely-available multi-channel audio compression codecs are not designed to consider the characteristic inter-channel relations inherent to the Ambisonics format, and thus may not leverage this knowledge to optimise the compression. Therefore, this article proposes a spatial audio compression algorithm, based on a novel reformulation of the Higher-Order Directional Audio Coding (HO-DirAC) method, which is specifically intended for compressing higher-order Ambisonic audio streams. The methodology builds upon the concept of a spherical filter bank acting in the spherical harmonic domain. This results in directionally constrained sound-field estimates and parameterization, which may be utilized to reconstruct the input Ambisonic signals with minimal perceived loss of quality. The results of a listening experiment indicate high perceptual quality when using six or more audio transport channels to deliver fifth-order (36 channels) Ambisonic sound scenes. The proposed formulation is also designed with low computational complexity in mind and may therefore be well suited for compressing Ambisonic sound scenes for a wide range of applications.