Shared Filter Bank Harmonic Transposition for Efficient HFR
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Solution Overview
Problem
Existing harmonic transposition methods for high frequency reconstruction in audio coding systems require multiple filter banks for different transposition orders, leading to increased computational complexity and inefficiency, especially when upsampling is needed.
Innovation Solution
The method involves sharing a common analysis and synthesis filter bank pair among multiple harmonic transposers, using nonlinear processing to map nonlinearly modified subband signals from the analysis filter bank to selected subbands in the synthesis filter bank, allowing for efficient generation of high frequency components with reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple filter banks are used for different transposition orders, then the accuracy of high frequency reconstruction is improved, but the computational complexity increases significantly
Solution Approach 1:
The patent applies universality by designing a single analysis filter bank and a single synthesis filter bank that can be shared across multiple transposition orders. The analysis filter bank decomposes the input signal into subbands, and the synthesis filter bank reconstructs the signal from these subbands. By making these filter banks universal and order-independent, the system achieves multiple transposition orders without requiring separate filter banks for each order, thus resolving the contradiction between reconstruction accuracy and computational complexity
Solution Approach 2:
The patent applies segmentation by dividing the signal processing into distinct stages: analysis filter bank decomposition, nonlinear processing with order-specific phase modification, and synthesis filter bank reconstruction. This segmentation allows the common filter banks to be used across different transposition orders while maintaining the ability to achieve accurate reconstruction through proper subband manipulation and phase adjustment
2Reliability
If multiple filter banks are used for different transposition orders, then the quality of synthesized high band signal is improved, but the number of components and system structure becomes more complex
Solution Approach 1:
The patent makes the analysis and synthesis filter banks universal components that serve all transposition orders. Instead of having separate filter banks for each transposition order, a single pair of filter banks is designed to handle all orders by processing subbands and applying order-specific nonlinear operations. This reduces the number of components while maintaining signal quality through proper subband manipulation
Solution Approach 2:
The patent merges the functionality of multiple filter banks into a single shared analysis filter bank and a single shared synthesis filter bank. By combining these components and using them across different transposition orders, the system reduces the total number of components while maintaining the ability to synthesize high band signals of various qualities through nonlinear processing and phase modification
3Speed
If upsampling is performed to convert core signal to output sampling rate, then the bandwidth of the output signal is improved, but additional filter banks are required increasing complexity
Solution Approach 1:
The patent applies universality by designing the analysis and synthesis filter banks to inherently handle sampling rate conversion. The same filter banks used for transposition also perform the upsampling function by processing subbands at different rates and reconstructing the signal at the desired output sampling rate. This eliminates the need for separate upsampling filter banks, resolving the contradiction between bandwidth improvement and complexity increase
Data Source
AI summary
The present document relates to audio coding systems which make use of a harmonic transposition method for high frequency reconstruction (HFR), and to digital effect processors, e.g. so-called exciters, where generation of harmonic distortion adds brightness to the processed signal. In particular; a system configured to generate a high frequency component of a signal from a low frequency component of the signal is described, The system may comprise an analysis filter bank (501) configured to provide a set of analysis subband signals from the low frequency component of the signal; wherein the set of analysis subband signals comprises at least two analysis subband signals; wherein the analysis filter bank (501) has a frequency resolution of Δf, The system further comprises a nonlinear processing unit (502) configured to determine a set of synthesis subband signals from the set of analysis subband signals using a transposition order P; wherein the set of synthesis subband signals comprises a portion of the set of analysis subband signals phase shifted by an amount derived from the transposition order P; and a synthesis filter bank (504) configured to generate the high frequency component of the signal from the set of synthesis subband signals; wherein the synthesis filter bank (504) has a frequency resolution of FΔf; with F being a resolution factor, with F≧1; wherein the transposition order P is different from the resolution factor F.