Bandwidth Extension Patching for Spectral Gap Filling in Audio
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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 computational inefficiencies and poor approximation of high-frequency bands, and existing bandwidth extension techniques fail to adequately fill spectral gaps and maintain audio quality.
Innovation Solution
A method and apparatus that generate a bandwidth extended signal by combining patches with different spectral densities, using harmonic and mixing algorithms to fill gaps in the high-frequency band, ensuring the spectral envelope of the original signal is maintained through patch scaling and combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If bandwidth extension is performed using existing techniques, then the bandwidth of the audio signal is increased, but spectral gaps remain and audio quality is not adequately maintained
Solution Approach 1:
The bandwidth extension process is segmented into multiple stages: generating a first patch using harmonic patching, generating a second patch using mixing patching, and combining both patches. This segmentation allows each patch to address specific spectral characteristics, with the second patch specifically targeting spectral gaps left by the first patch, thereby improving overall audio quality while extending bandwidth.
2Volume of moving object
If filterbank calculations and patching are performed in the filterbank domain, then bandwidth extension is achieved, but computational effort becomes very high
Solution Approach 1:
The invention extracts the essential spectral envelope information from the original signal and uses it to guide the patching process. By taking out only the necessary spectral characteristics rather than processing the entire signal through complex filterbank operations, the computational effort is significantly reduced while still achieving effective bandwidth extension.
Solution Approach 2:
The invention changes the processing approach from time-domain filterbank operations to frequency-domain spectral envelope manipulation. By working with spectral parameters directly and using scaling factors to adjust the patches, the computational complexity is reduced compared to traditional filterbank-based bandwidth extension methods.
3Volume of moving object
If the lower band is harmonically patched into the upper band, then bandwidth extension is achieved, but spectral gaps are not adequately filled
Solution Approach 1:
The invention merges two different patching approaches: harmonic patching (first patch) and mixing patching (second patch). The harmonic patch preserves tonal structure while the mixing patch fills in spectral gaps with noise-like content. By combining both patches, the invention simultaneously maintains tonal accuracy and fills spectral information gaps, achieving more complete bandwidth extension.
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.