Temporal Envelope Shaping for Spatial Audio Decoding
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Solution Overview
Problem
Block-based audio coding techniques limit the temporal envelope resolution of decoded audio signals, particularly affecting systems that do not preserve discrete channels, leading to issues like a narrowed or collapsed spatial image in reproduced audio, especially with complex signals like applause.
Innovation Solution
The method involves encoding audio signals into time blocks with side information updates limited by the block rate, comparing the temporal envelope of input signals with an estimated decoded reconstruction, and applying filter coefficients to improve temporal envelope resolution, which are then included in the bitstream for decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If block-based audio coding is used to reduce bit rate, then bit rate efficiency is improved, but temporal envelope resolution deteriorates
Solution Approach 1:
The patent segments the audio signal into frequency bands and processes each band independently with band-specific filter coefficients. This allows temporal envelope shaping to be applied selectively to different frequency regions, improving overall temporal resolution without uniformly increasing complexity across the entire spectrum.
Solution Approach 2:
The patent changes the temporal envelope parameters by computing filter coefficients that model the difference between original and reconstructed temporal envelopes. These coefficients are applied to reshape the decoded signal's temporal envelope, effectively increasing temporal resolution beyond the block rate limitation while maintaining bit rate efficiency.
2Loss of energy
If block-based coding without discrete channel preservation is used, then bit rate is reduced, but spatial image quality deteriorates
Solution Approach 1:
The patent applies different filter coefficients to different frequency bands, allowing temporal envelope shaping to be tailored to the specific characteristics of each band. This local processing approach preserves spatial image quality in frequency regions where it is most critical while maintaining bit rate efficiency in other regions.
Solution Approach 2:
The patent uses feedback by computing filter coefficients based on the difference between the original signal's temporal envelope and the reconstructed signal's temporal envelope. This closed-loop approach ensures that the temporal shaping accurately reconstructs the original spatial and temporal characteristics, preventing spatial image collapse.
Data Source
AI summary
Certain types of parametric spatial coding encoders use interchannel amplitude differences, interchannel time differences, and interchannel coherence or correlation to build a parametric model of a multichannel soundfield that is used by a decoder to construct an approximation of the original soundfield. However, such a parametric model does not reconstruct the original temporal envelope of the soundfield's channels, which has been found to be extremely important for some audio signals. The present invention provides for the reshaping the temporal envelope of one or more of the decoded channels in a spatial coding system to better match one or more original temporal envelopes.