Spatial Audio Encoding Significance Measure for Coherence Parameters
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Solution Overview
Problem
Current spatial audio encoding technologies face challenges in efficiently compressing and encoding coherence parameters, leading to high bitrates for spatial metadata, particularly in multi-channel audio systems, where the significance of coherence values varies across frequency bands and affects the subjective listening experience.
Innovation Solution
The proposed solution involves determining a significance measure for coherence values by calculating the proportion of coherent non-directional energy and normalizing it with the non-directional energy ratio, allowing for selective encoding of coherence parameters based on their subjective significance, thereby reducing the overall bitrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherence parameters are encoded for all sub-bands, then spatial audio quality is maintained, but bitrate increases
Solution Approach 1:
The patent applies local quality by determining significance measures for coherence parameters on a per-sub-band basis rather than uniformly across all frequencies. The significance measure calculation considers the proportion of coherent non-directional energy specific to each sub-band, allowing the encoding decision to be tailored to the actual acoustic content and perceptual importance of each frequency region. This resolves the contradiction by maintaining high spatial audio quality only where coherence parameters are actually significant, while avoiding bitrate waste in sub-bands where they are not.
Solution Approach 2:
The patent implements partial action by selectively encoding coherence parameters only for sub-bands where the significance measure exceeds a threshold, rather than encoding all coherence parameters. The significance measure is calculated as the proportion of coherent non-directional energy, and only sub-bands with sufficiently high values contribute to the encoded bitstream. This partial encoding approach maintains perceptual quality while substantially reducing the quantity of data that needs to be transmitted.
2Measurement precision
If coherence parameters are encoded for all sub-bands, then spatial metadata accuracy is improved, but compression efficiency deteriorates
Solution Approach 1:
The patent changes the parameter representation by introducing a significance measure that is a function of the proportion of coherent non-directional energy. This significance measure serves as a gating parameter that determines whether coherence parameters should be encoded for each sub-band. By changing from a uniform encoding approach to a significance-based selective encoding approach, the system achieves both high spatial metadata accuracy (where needed) and improved compression efficiency (by excluding insignificant parameters).
Solution Approach 2:
The patent segments the frequency spectrum into multiple sub-bands and applies different encoding decisions to each segment based on its significance measure. Rather than treating all frequencies uniformly, the system divides the spectrum and independently evaluates the coherence parameter significance in each segment. This segmentation allows the encoder to maintain accuracy in important frequency regions while achieving compression efficiency by omitting parameters in less important regions.
3Reliability
If all spatial audio parameters are encoded, then reproduction fidelity is maintained, but bit usage increases
Solution Approach 1:
The patent extracts and identifies the essential component for spatial perception as the proportion of coherent non-directional energy, which forms the basis of the significance measure. By taking out this key characteristic and using it to gate the encoding of coherence parameters, the system maintains reproduction fidelity for perceptually important parameters while discarding (not encoding) parameters that do not contribute to fidelity. This extraction approach directly addresses the contradiction by separating essential from non-essential data.
Solution Approach 2:
The patent applies partial action by encoding only the subset of spatial audio parameters (coherence parameters in significant sub-bands) that contribute to reproduction fidelity, rather than encoding all parameters. The significance measure identifies which parameters are necessary for faithful reproduction, and only those are included in the encoded bitstream. This partial encoding maintains fidelity where it matters while minimizing bit usage.
Data Source
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AI summary
There is inter alia disclosed an apparatus for spatial audio encoding which can receive or determine for one or more audio signals (102), spatial audio parameters (106) on a sub band basis for providing spatial audio reproduction, the spatial audio parameters can comprise a coherence value (112) for each sub band of a plurality of subbands (202) of a frame. The apparatus then determines a significance measure for the coherence values (401) of the plurality of sub bands of the frame and uses the significance measure to determine whether to encode (403) the coherence values of the plurality of sub bands of the frame.