Harmonic Transposition with Adaptive Window Length
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Solution Overview
Problem
Existing harmonic transposition methods face challenges in achieving good transient performance without the need for window switching, and they often require high frequency resolution, which can be detrimental for transient signal processing.
Innovation Solution
The proposed solution involves oversampling in frequency by a factor related to the transposition factor, appropriate choice of analysis and synthesis windows, and ensuring time-alignment of transposed signals, all while minimizing additional complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency resolution is used in harmonic transposition, then transposition quality for stationary sounds is improved, but transient response deteriorates
Solution Approach 1:
The patent applies dynamics by making the window length adaptive rather than fixed. The system automatically adjusts window length based on signal characteristics: using long windows for stationary sounds to achieve high frequency resolution, and short windows for transient sounds to maintain good transient response. This dynamic adaptation resolves the contradiction between frequency resolution and transient response.
2Speed
If window switching is implemented to improve transient performance, then transient response is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic window length selection that adapts to signal characteristics without requiring manual window switching. The system automatically determines the appropriate window length based on the detected signal type (stationary or transient), eliminating the need for complex window switching mechanisms while maintaining good transient performance.
3Measurement precision
If long windows are used to achieve high frequency resolution, then frequency resolution is improved, but transient detection capability deteriorates
Solution Approach 1:
The patent resolves this contradiction by making window length dynamic. The system detects transient characteristics in the signal and automatically switches to short windows when transients are detected, enabling both high frequency resolution for stationary sounds and effective transient detection for transient sounds.
Data Source
AI summary
The present invention relates to transposing signals in time and/or frequency and in particular to coding of audio signals. More particular, the present invention relates to high frequency reconstruction (HFR) methods including a frequency domain harmonic transposer. A method and system for generating a transposed output signal from an input signal using a transposition factor T is described. The system comprises an analysis window of length La, extracting a frame of the input signal, and an analysis transformation unit of order M transforming the samples into M complex coefficients. M is a function of the transposition factor T. The system further comprises a nonlinear processing unit altering the phase of the complex coefficients by using the transposition factor T, a synthesis transformation unit of order M transforming the altered coefficients into M altered samples, and a synthesis window of length Ls, generating a frame of the output signal.