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 gaps and energy imbalances in the reconstructed high-frequency bands, which are not adequately addressed by current harmonic transposition, phase vocoder, or noise addition techniques.
Innovation Solution
A method involving a patch generator that creates two patches from a lower resolution band of an input signal using different patching algorithms, where the second patch has a higher spectral density than the first, and a combiner that combines these patches with the input signal to form a bandwidth extended signal, ensuring the spectral envelope matches the original signal.
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 in the high-frequency band are not adequately filled
Solution Approach 1:
The patent combines two different patching algorithms (first patching algorithm and second patching algorithm) to generate two different patches from the low-frequency band. These patches are then merged together, where the first patch provides the spectral envelope and the second patch fills in the spectral gaps, achieving both computational efficiency and high spectral reconstruction accuracy.
2Quantity of substance
If the high-frequency band is coarsely characterized using spectral envelope parameters only, then the data rate is reduced, but the subjective audio quality deteriorates
Solution Approach 1:
The patent changes the parameter representation of the high-frequency band from a single spectral envelope parameter to a combination of two patches with different spectral densities. The first patch uses spectral envelope parameters for data reduction, while the second patch adds finer spectral details, thereby improving audio quality without proportionally increasing data rate.
3Manufacturing precision
If harmonic transposition is used to extend the bandwidth, then the spectral envelope is preserved, but the computational effort becomes very high
Solution Approach 1:
The patent segments the bandwidth extension process into two distinct patching operations instead of using a single complex harmonic transposition. The first patching algorithm handles the spectral envelope preservation, while the second patching algorithm handles the spectral gap filling, dividing the computational task into manageable segments that are more efficient than full harmonic transposition.
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.