Layered HOA Coding for Low-Bitrate Sound Field Decoding
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Solution Overview
Problem
Conventional HOA layered coding fails to enhance partially reconstructed representations, especially at low bitrates, and the V-vector elements are not appropriately decoded in vector coding mode, leading to unsuitable decoding for layers below the highest layer.
Innovation Solution
A method for layered encoding of compressed HOA representations that assigns transport signals to hierarchical layers, generates HOA extension payloads for each layer, and signals them in the bitstream, ensuring appropriate enhancement of reconstructed sound representations even at low bitrates, with error protection tailored to each layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional HOA layered coding is used with side information only for the highest layer, then device complexity is reduced and bandwidth is saved, but sound quality at low bitrates deteriorates because lower layers cannot be properly enhanced
Solution Approach 1:
The patent segments the enhancement side information into layer-specific components, where each layer has its own set of enhancement parameters rather than sharing a single set for all layers. This allows independent optimization of enhancement for each layer while maintaining overall system efficiency.
Solution Approach 2:
The patent applies local quality by providing differentiated enhancement side information tailored to each specific layer's needs. Lower layers receive enhancement parameters optimized for their characteristics, while higher layers receive their own specialized parameters, ensuring each layer achieves optimal quality for its bitrate level.
2Ease of operation
If V-vector elements are set to zero for indices in ContAddHoaCoeff set, then decoding simplicity is improved, but decoding accuracy deteriorates in layered coding mode because the assumption that vector signal should not contribute is wrong for coefficients missing in lower layers
Solution Approach 1:
The patent introduces dynamic behavior to the V-vector element assignment by making the value depend on layer information. Instead of a static zero assignment, the system dynamically determines whether to use zero or the V-vector element based on whether the corresponding coefficient index exists in the current layer's ContAddHoaCoeff set, allowing adaptive optimization for each layer.
Solution Approach 2:
The patent changes the parameter assignment strategy by introducing layer-dependent parameter selection. The V-vector element value is no longer a fixed parameter but varies based on the layer context, specifically whether the coefficient index is present in that layer's ContAddHoaCoeff set, enabling accurate reconstruction for each layer's specific coefficient set.
Data Source
AI summary
The present document relates to a method of layered encoding of a frame of a compressed higher-order Ambisonics, HOA, representation of a sound or sound field. The compressed HOA representation comprises a plurality of transport signals. The method comprises assigning the plurality of transport signals to a plurality of hierarchical layers, the plurality of layers including a base layer and one or more hierarchical enhancement layers, generating, for each layer, a respective HOA extension payload including side information for parametrically enhancing a reconstructed HOA representation obtainable from the transport signals assigned to the respective layer and any layers lower than the respective layer, assigning the generated HOA extension payloads to their respective layers, and signaling the generated HOA extension payloads in an output bitstream. The present document further relates to a method of decoding a frame of a compressed HOA representation of a sound or sound field, an encoder and a decoder for layered coding of a compressed HOA representation, and a data structure representing a frame of a compressed HOA representation of a sound or sound field.