Harmonic Transposition Filter Bank for Low-Complexity 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 implements a universal filter bank structure that can perform multiple transposition operations (T=2, T=3, T=4) using the same analysis and synthesis filter banks. The filter bank pair is configured with sufficient frequency resolution to handle different transposition orders, eliminating the need for separate filter banks for each transposition order while maintaining reconstruction accuracy
Solution Approach 2:
The patent changes the operational parameters of the universal filter bank by adjusting the transposition order parameter T and the subband selection parameter k. By modifying these parameters rather than the filter bank structure itself, the system can adapt to different transposition orders without requiring multiple dedicated filter banks, thus reducing computational complexity while maintaining accuracy
2Device complexity
If a single filter bank pair is shared among multiple transposers, then the computational complexity is reduced, but the ability to accurately reconstruct high frequencies for all transposition orders may be compromised
Solution Approach 1:
The patent segments the frequency spectrum into multiple subbands using the universal filter bank. By carefully selecting which subbands to process for each transposition order and using the mapping relationship between analysis subband index k and synthesis subband index n, the system accurately reconstructs high frequencies for different transposition orders using the same filter bank pair
Solution Approach 2:
The patent implements dynamic parameter adjustment where the transposition order T and subband selection k can be changed based on the input signal characteristics and desired output. This dynamic adaptability allows the universal filter bank to maintain high reconstruction accuracy across different transposition scenarios without requiring dedicated filter banks for each case
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.