This paper presents a parametric joint channel coding scheme that enables the delivery of channel-based immersive audio content in formats such as 7.1.4, 5.1.4, or 5.1.2 at very low bit rates. It is based on a generalized approach for parametric spatial coding of groups of two, three, or more channels using a single downmix channel together with a compact parametrization that guarantees full covariance re-instatement in the decoder. By arranging the full-band channels of the immersive content into five groups, the content can be conveyed as a 5.1 downmix together with the parameters for each group. This coding scheme is implemented in the A-JCC tool of the AC-4 system recently standardized by ETSI, and listening test results illustrate its performance.
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