Frequency-Domain Harmonic Transposition Without Window-Switching Artifacts
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Solution Overview
Problem
Existing harmonic transposition methods face challenges in achieving high frequency resolution for stationary sounds while maintaining good transient response, often leading to signal artifacts due to window switching and increased complexity.
Innovation Solution
The method employs frequency oversampling and appropriate choice of analysis and synthesis windows, along with time-alignment of transposed signals, to improve transient performance without the need for window switching, ensuring minimal additional complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high frequency resolution is used to achieve high quality transposition for stationary sounds, then the frequency resolution is improved, but the time response for transient or percussive sounds deteriorates due to large window sizes
Solution Approach 1:
The patent applies dynamics by making the window size adaptive rather than fixed. The method automatically adjusts the analysis and synthesis window lengths based on the signal characteristics - using long windows for stationary portions to achieve high frequency resolution, and short windows for transient portions to maintain good temporal resolution. This dynamic adaptation eliminates the need for manual window switching while resolving the contradiction between frequency and time resolution.
Solution Approach 2:
The patent changes the parameter of window size dynamically. By modifying the window length parameter according to the local signal characteristics (stationary vs. transient), the system optimizes both frequency resolution and time response performance. The parameter adaptation is based on measuring signal stability and adjusting window sizes accordingly, thereby resolving the trade-off between these two opposing requirements.
2Speed
If window switching is used to adapt to different signal characteristics, then the transient response is improved, but signal artifacts are introduced and system complexity increases
Solution Approach 1:
The patent employs dynamic window size adaptation that transitions smoothly between different window lengths based on signal characteristics. This dynamic approach maintains good transient response while avoiding the abrupt transitions that cause artifacts. The system continuously monitors signal stability and adjusts window sizes渐变地, preventing the discontinuities that would otherwise generate audible artifacts.
Solution Approach 2:
The patent performs preliminary analysis of signal characteristics to determine appropriate window sizes before processing each frame. By pre-adapting the window parameters based on local signal properties, the system prepares the optimal processing configuration in advance, avoiding abrupt changes during processing that would generate artifacts. This preliminary adaptation ensures smooth transitions and maintains signal quality.
3Speed
If adaptive window switching is implemented to handle transient and stationary portions, then transient response is improved, but device complexity increases due to additional signal analysis measures
Solution Approach 1:
The patent implements a dynamic window size adaptation mechanism that automatically adjusts processing parameters based on signal characteristics. The system includes a signal analysis component that detects transient vs. stationary portions, and a window size selection component that adapts accordingly. This dynamic adaptation achieves good transient response without requiring complex manual intervention or multiple fixed processing paths.
Solution Approach 2:
The patent changes the window size parameter adaptively based on signal analysis results. By modifying this key parameter dynamically, the system achieves optimal transient response for different signal types. The parameter adaptation is driven by simple signal stability measurements rather than complex analysis, keeping the overall system complexity manageable while maintaining high performance.
Data Source
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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.