Bandwidth Extension Signal Generation With Dual-Density Patches
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Solution Overview
Problem
Existing audio coding methods, particularly at low bit rates, reduce subjective audio quality due to bandwidth limitations, leading to gaps and energy imbalances in the high-frequency spectrum, which are inadequately addressed by current bandwidth extension techniques such as harmonic transposition and phase vocoders.
Innovation Solution
A method involving two patching algorithms is used to generate patches with different spectral densities, where a first patch with lower spectral density is combined with a second patch having higher spectral density to fill gaps, while ensuring the spectral envelope of the original signal is maintained through scaling, thereby improving audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If bandwidth extension is performed using a single patching algorithm, then the computational complexity is reduced, but the spectral gaps remain unfilled and audio quality deteriorates
Solution Approach 1:
The patent divides the bandwidth extension process into multiple patches generated by different patching algorithms. Each patch targets specific spectral gaps with different spectral densities, allowing selective filling of gaps without processing the entire spectrum uniformly. This segmentation resolves the contradiction by applying complexity only where spectral gaps exist rather than across the full bandwidth.
Solution Approach 2:
The patent applies different patching algorithms to different spectral regions based on local characteristics. High spectral density patches are applied where spectral gaps are prominent, while lower density patches are used where the spectrum is already dense. This local adaptation fills spectral gaps accurately without uniformly increasing computational complexity across all frequency bands.
2Manufacturing precision
If multiple patching algorithms are used to fill spectral gaps, then the spectral envelope accuracy is improved, but the computational complexity increases
Solution Approach 1:
The patent applies multiple patching algorithms selectively rather than exhaustively. Instead of applying all possible patches to the entire spectrum, the system identifies specific spectral gaps and applies only the necessary patches to fill them. This partial action approach maintains spectral envelope accuracy while avoiding the full computational burden of processing the entire spectrum with multiple algorithms.
3Manufacturing precision
If the spectral density is increased in the high frequency band, then the audio quality is improved, but the energy distribution becomes unnatural
Solution Approach 1:
The patent adjusts the spectral density parameter of patches based on the local characteristics of the target frequency band. Rather than uniformly increasing spectral density across all high frequencies, the system modifies patch density and energy distribution to match the natural spectral envelope of the original signal. This parameter adaptation improves audio quality while preserving natural energy distribution patterns.
Data Source
AI summary
An apparatus for generating a bandwidth extended signal from an input signal includes a patch generator and a combiner. The input signal is represented for first and second bands by first and second resolution data, respectively, the second resolution being lower than the first. The patch generator generates first and second patches from the first band of the input signal according to first and second patching algorithms, respectively. A spectral density of the second patch generated using the second patching algorithm is higher than a spectral density of a first patch generated using the first patching algorithm. The combiner combines both patches and the first band of the input signal to obtain the bandwidth extended signal. The apparatus scales the input signal according to the first and second patching algorithms or scales the first and second patches, so that the bandwidth extended signal fulfills a spectral envelope criterion.