Efficient combined harmonic transposition
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Solution Overview
Problem
Existing harmonic transposition methods 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, utilizing nonlinear processing to map 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 universal filter bank structure that serves multiple transposition orders simultaneously. The same analysis filter bank and synthesis filter bank are reused across different transposition operations, allowing one filter bank pair to perform the function of what would traditionally require multiple separate filter banks. This multi-functional approach maintains reconstruction accuracy while eliminating redundant computational operations.
Solution Approach 2:
The patent merges the functionality of multiple separate filter banks into a single shared filter bank structure. By combining the analysis and synthesis filter banks into a reusable pair that serves all transposition orders, the system consolidates what would be multiple independent processing chains into one unified structure, thereby reducing overall computational complexity while preserving the necessary filtering functionality for accurate high frequency reconstruction.
2Adaptability or versatility
If multiple filter banks are implemented for different transposition orders, then the bandwidth extension capability is improved, but the processing time increases
Solution Approach 1:
The patent performs preliminary action by pre-computing and storing the filter bank coefficients in a lookup table during system initialization. This allows the filter bank operations to be executed efficiently during actual transposition operations by simply retrieving pre-computed values, thereby reducing processing time while maintaining the capability to handle multiple transposition orders and achieve effective bandwidth extension.
3Productivity
If a single filter bank pair is shared among multiple transposers, then the computational efficiency is improved, but the difficulty of coordinating subband signal mapping increases
Solution Approach 1:
The patent applies segmentation by dividing the frequency spectrum into distinct subband regions, each handled by specific transposition operations. The analysis filter bank decomposes the input signal into multiple subbands, and each subband is processed according to its specific transposition requirements. This segmented approach to frequency domain processing makes the coordination of subband signal mapping more manageable while maintaining computational efficiency through the shared filter bank structure.
Solution Approach 2:
The patent introduces an intermediary frequency domain processing stage that mediates between the shared filter bank and the multiple transposition operations. This intermediary stage handles the coordination of subband signal mapping by providing a standardized interface for converting subband signals between different transposition orders, thereby simplifying the coordination complexity while enabling efficient reuse of the filter bank structure.
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 factorF.