Ambisonics Coding in IVAS: A Hybrid SPAR and DirAC System

The Ambisonics audio format represents a 3D sound field as a fixed set of audio channels, with a tradeoff between spatial detail and the required number of audio channels. Because the number of audio channels that must be coded increases quadratically with respect to Ambisonics order, high-quality coding of Ambisonics signals under practical bitrate and complexity constraints becomes a major challenge. To overcome this, the 3GPP IVAS codec employs a new hybrid parametric and residual coding scheme combining complementary Spatial Reconstruction (SPAR) and Directional Audio Coding (DirAC) techniques. In this paper, we describe the implementation of this hybrid coding system and demonstrate its advantages to discrete channel-coding approaches in terms of computational complexity and audio quality.