Bass Post-Filter Adaptation via Discontinuity Measurement
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Solution Overview
Problem
The bass post-filter in audio decoding can introduce discontinuities and artefacts, particularly due to abrupt changes in parameters, which are not adequately addressed by existing adaptation methods that focus on gradual transitions and correlation analysis.
Innovation Solution
A method and decoder that measure the size of discontinuities in the post-filter difference signal and form a decision variable based on the energy ratio between the average energy of these discontinuities and the energy estimate of the frequency spectrum, comparing it to a threshold to determine whether to activate or deactivate the post-filter, thereby mitigating artefacts while maintaining filter benefits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bass post-filter is applied to improve audio quality, then noise reduction and spectral enhancement are achieved, but discontinuities and artefacts are introduced due to abrupt parameter changes
Solution Approach 1:
The patent measures discontinuities in the post-filter difference signal before making the decision to activate or deactivate the filter. By anticipating problematic regions through discontinuity measurement and energy ratio analysis, the system can prevent artefact introduction while maintaining the filter's noise reduction benefits in suitable regions
Solution Approach 2:
The patent dynamically adapts the bass post-filter by making it switchable between active and inactive states based on real-time analysis of discontinuities and energy ratios. This dynamic control allows the filter to be enabled when beneficial and disabled when harmful, resolving the contradiction between noise reduction and artefact prevention
2Stability of the object's composition
If existing adaptation methods use gradual transitions and correlation analysis, then smooth parameter changes are achieved, but computational complexity increases and discontinuities are not adequately addressed
Solution Approach 1:
The patent extracts and focuses specifically on measuring discontinuities in the post-filter difference signal at subframe boundaries, rather than using comprehensive correlation analysis. This targeted approach adequately addresses discontinuities while maintaining low computational complexity by measuring only the essential discontinuity metric
Solution Approach 2:
The patent changes the adaptation parameter from correlation-based gradual transitions to discontinuity-based switchable control. By forming a decision variable from the energy ratio of discontinuities to signal energy and comparing it to a threshold, the system achieves effective filter control with reduced computational complexity
Data Source
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AI summary
A method and a decoder for audio decoding, where an encoded signal is decoded to form a decoded signal, and an energy estimate of at least a part of a frequency spectrum of the decoded signal is obtained. A post-filter difference signal that describes the difference between a post-filtered decoded signal and a non-filtered decoded signal in time domain is generated, and size of discontinuities is measured by averaging the step at subframe boundaries of the post-filter difference signal. A decision variable is formed based on a ratio between average energy of the step at the subframe boundaries and the energy estimate. The decision variable is compared to a threshold and the output signal is set to be the decoded signal or the post-filtered signal as a result of the comparison.