Bandwidth Extension Patching for Low-Bitrate Audio Quality
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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 the upper band in synthesized audio signals.
Innovation Solution
A method involving a patch generator that creates two patches from a lower resolution band of an input signal, one with a harmonic and one with a mixing algorithm, to fill gaps and enhance spectral density, combined with a combiner to ensure the bandwidth extended signal meets a spectral envelope criterion.
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 density is insufficient and gaps remain in the frequency spectrum
Solution Approach 1:
The patent divides the bandwidth extension process into multiple segments by applying different patching algorithms (harmonic and mixing) to generate separate patches. Each algorithm addresses specific spectral gaps, and the patches are combined to achieve complete spectral coverage without excessive computational complexity.
Solution Approach 2:
The patent applies different patching algorithms in different spectral regions or for different patch types. The harmonic patching algorithm is used for certain frequency regions while the mixing algorithm is used for others, optimizing the spectral density distribution across the entire bandwidth according to local spectral characteristics.
2Quantity of substance
If the upper band is coarsely characterized with limited parameters, then the data rate is reduced, but the approximation quality of the synthesized upper band deteriorates
Solution Approach 1:
The patent copies spectral characteristics from the lower band to the upper band through patching algorithms. By replicating and transforming lower band spectral information into upper band patches, the system achieves accurate upper band approximation without transmitting extensive upper band data, thus maintaining low data rate while improving quality.
3Manufacturing precision
If filterbank calculations and patching are performed in the filterbank domain, then the bandwidth extension accuracy is improved, but the computational effort increases significantly
Solution Approach 1:
The patent extracts essential spectral characteristics from the filterbank domain and processes them in a simplified representation domain. By taking out only the necessary spectral parameters and processing them through the patching algorithms, the system maintains bandwidth extension accuracy while significantly reducing the computational effort compared to full filterbank domain processing.
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.