Harmonic Transposition Filter Banks 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, utilizing nonlinear processing to map subband signals across different transposition orders, and employing advanced nonlinear processing techniques to reduce the number of required filter banks and simplify the transposition process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple filter banks are used for different transposition orders, then the audio quality and bandwidth synthesis are 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) by reconfiguring the same hardware resources. The filter bank is designed to be multi-functional, where the same filters and processing units can be reused across different transposition orders through time-multiplexing and parameter reconfiguration, eliminating the need for separate dedicated filter banks for each transposition order.
Solution Approach 2:
The patent employs a nested structure where transposition stages are organized hierarchically. The output of one transposition stage becomes the input for the next stage, with T=2 transposition feeding into T=3, which feeds into T=4. This nesting allows shared resources and progressive bandwidth expansion, reducing overall computational complexity compared to independent parallel processing of all transposition orders.
2Adaptability or versatility
If multiple filter banks are used for different transposition orders, then the required bandwidth of the high band signal is synthesized, but the resource requirements increase
Solution Approach 1:
The filter bank is designed as a universal resource that can be dynamically reconfigured to support multiple transposition orders. The same filter bank infrastructure serves T=2, T=3, and T=4 operations by adjusting operational parameters and timing, significantly reducing the quantity of hardware resources needed compared to having dedicated filter banks for each transposition order.
Solution Approach 2:
The patent merges multiple transposition operations into a unified processing pipeline. Instead of having separate independent filter bank systems for each transposition order, the operations are combined into a single integrated system where resources are shared and coordinated, reducing overall resource consumption while maintaining the ability to synthesize the required high band signal bandwidth.
3Speed
If upsampling is added to convert core signal to output sampling rate, then the sampling rate conversion is achieved, but the device complexity increases
Solution Approach 1:
The upsampling function is merged with the existing filter bank structure used for transposition operations. The same filter bank that performs frequency domain transposition also handles the sampling rate conversion by operating as an upsampler when needed. This integration eliminates the need for a separate dedicated upsampling module, reducing device complexity while achieving the required sampling rate conversion from the core signal to the final output rate.
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.