Shared Filter Banks for Harmonic Transposition in Audio 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 advanced nonlinear processing to map nonlinearly modified subband signals across different transposition orders, allowing for efficient frequency domain transposition and reducing the need for multiple filter banks.
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 single analysis filter bank and a single synthesis filter bank that serve multiple transposition orders simultaneously. The analysis filter bank decomposes the input signal into subbands that can be processed for different transposition orders, and the synthesis filter bank reconstructs the signal by combining results from multiple transposition operations. This multi-functional approach eliminates the need for separate filter banks for each transposition order, thereby maintaining reconstruction accuracy while significantly reducing computational complexity.
Solution Approach 2:
The patent merges multiple filter bank operations into a unified structure where a single analysis filter bank and single synthesis filter bank handle all transposition orders. By combining the filtering operations and sharing the filter bank resources across different transposition processes, the system achieves the same reconstruction quality without the redundant computational overhead of multiple separate filter banks.
2Reliability
If multiple filter banks are used for different transposition orders, then the quality of synthesized bandwidth is improved, but the system becomes less efficient
Solution Approach 1:
The analysis and synthesis filter banks are designed to be universal components that can process signals for multiple transposition orders without requiring separate instances. This multi-functionality ensures that audio quality is maintained across different transposition operations while improving processing efficiency by eliminating redundant filter bank computations.
Solution Approach 2:
The patent discards the redundant filter banks for each transposition order and recovers the necessary filtering functionality through the shared analysis and synthesis filter banks. By eliminating unnecessary duplicate components while preserving the essential filtering capabilities, the system achieves both high audio quality and improved processing efficiency.
3Adaptability or versatility
If upsampling is added to convert core signal to output sampling rate, then the compatibility of the system is improved, but the device complexity increases
Solution Approach 1:
The upsampling operation is merged with the existing synthesis filter bank structure. The synthesis filter bank is configured to perform both the filtering and upsampling operations in a unified process, eliminating the need for a separate upsampling stage. This integration maintains sampling rate compatibility while avoiding the additional complexity of independent upsampling components.
Solution Approach 2:
The synthesis filter bank is designed with multi-functionality to handle both signal reconstruction and sampling rate conversion. By making the synthesis filter bank universal enough to perform upsampling as part of its reconstruction process, the system achieves sampling rate compatibility without adding separate upsampling hardware or software modules.
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 P is different from the resolution factor F.