Harmonic Transposition Filter Bank for Efficient High-Frequency Reconstruction
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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 to match the sampling rate of the output signal.
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 transposition of high frequency components without the need for multiple filter banks for each transposition order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing 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:
A single filter bank is designed to perform multiple functions by supporting different transposition orders through parameter configuration. The filter bank can be adapted to work with various transposition orders (T=2, T=3, etc.) without requiring separate dedicated filter banks for each order, thereby reducing computational complexity while maintaining reconstruction accuracy.
Solution Approach 2:
The filter bank operates with variable parameters that can be adjusted according to the required transposition order. By changing parameters such as decimation factors and filter coefficients dynamically, the same filter bank structure can accommodate different transposition scenarios, eliminating the need for multiple fixed filter banks.
2Manufacturing precision
If multiple filter banks are used for different transposition orders, then the quality of high frequency reconstruction is improved, but the number of components in the system increases
Solution Approach 1:
The filter bank is designed as a universal component that can serve multiple transposition orders. Instead of having separate filter banks for each transposition order, a single configurable filter bank is implemented that can be adapted to different orders through parameter settings, thereby reducing the total number of components in the system.
Solution Approach 2:
Multiple filter bank functions are merged into a single filter bank structure. The system combines the functionality of what would otherwise require separate filter banks into one unified component that handles different transposition orders through parameter variation, reducing system complexity and component count.
3Adaptability or versatility
If upsampling is added to convert core signal to output sampling rate, then the compatibility with output signal is improved, but the computational complexity increases
Solution Approach 1:
The filter bank is designed to handle both transposition and upsampling functions within a single unified structure. By integrating these functions, the system achieves sampling rate compatibility without adding separate upsampling stages, thereby maintaining adaptability while controlling computational complexity.
Solution Approach 2:
The upsampling operation is merged with the filter bank processing. Instead of implementing upsampling as a separate subsequent stage, the filter bank is configured to perform both the transposition filtering and the sampling rate conversion in an integrated manner, reducing overall system complexity.
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.