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 allows sharing of analysis and synthesis filter banks among multiple harmonic transposers, using advanced nonlinear processing to map nonlinearly modified subband signals from an analysis filter bank into selected subbands of a synthesis filter bank, enabling efficient frequency domain transposition and reducing 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 where a single analysis filter bank and synthesis filter bank serve multiple transposition orders (T=2, T=3, T=4, etc.). Instead of requiring separate filter banks for each transposition order, the same filter bank pair is reused across different orders, with the filter bank being configured to handle the specific transposition order through parameter adjustment rather than structural duplication. This multi-functional approach maintains reconstruction accuracy across multiple orders while dramatically reducing computational complexity.
Solution Approach 2:
The patent employs parameter changes to adapt the filter bank behavior for different transposition orders. By modifying operational parameters (such as decimation factors, filter lengths, or frequency mappings) rather than changing the fundamental filter bank structure, the system can efficiently support multiple transposition orders using the same hardware/software resources, thus resolving the contradiction between accuracy and complexity.
2Reliability
If multiple filter banks are used for different transposition orders, then the quality of synthesized high band signal is improved, but the implementation efficiency deteriorates
Solution Approach 1:
The filter bank pair is designed to universally support multiple transposition orders through configurable parameters. The analysis filter bank decomposes the input signal into subbands, and the synthesis filter bank reconstructs the high band signal, with both banks capable of operating across different transposition orders without requiring separate instances, thereby improving implementation efficiency while maintaining signal quality.
Solution Approach 2:
The patent merges the functionality of multiple separate filter banks into a single shared filter bank pair. By combining the analysis and synthesis operations into a unified structure that serves multiple transposition orders, the system achieves both high signal quality and improved implementation efficiency through resource consolidation and shared processing paths.
3Adaptability or versatility
If upsampling is added to convert core signal to output sampling rate, then the compatibility with final output signal is improved, but the device complexity increases
Solution Approach 1:
The filter bank pair is designed to perform both transposition and upsampling functions universally. The analysis filter bank can operate at the core signal sampling rate while the synthesis filter bank outputs at the final output sampling rate, with the upsampling ratio embedded in the transposition operation itself. This multi-functional design achieves sampling rate compatibility without requiring separate upsampling filter banks, thus avoiding additional complexity.
Data Source
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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 Pis different from the resolution factorF.