Harmonic Transposition With Oversampling for Cleaner Transients
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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 without introducing signal artifacts, particularly due to the need for window switching and signal analysis measures.
Innovation Solution
The method employs frequency oversampling and appropriate selection of analysis and synthesis windows, along with time-alignment of transposed signals, to improve transient performance without window switching, ensuring minimal additional complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high frequency resolution is used in harmonic transposition, then the transposition quality for stationary sounds is improved, but the transient response deteriorates due to large window sizes
Solution Approach 1:
The patent applies dynamics by making the window size adaptive rather than fixed. The window size automatically adjusts based on the characteristics of the input signal - using larger windows for stationary portions to achieve high frequency resolution, and smaller windows for transient portions to maintain good transient response. This dynamic adaptation eliminates the need for manual window switching while resolving the contradiction between frequency resolution and transient response.
Solution Approach 2:
The patent changes the parameter of window size based on signal characteristics. By monitoring the input signal and adjusting the window size parameter accordingly, the system achieves high frequency resolution when needed while maintaining fast transient response when required. This parameter adaptation directly addresses the technical contradiction by allowing the system to optimize for different operational conditions.
2Speed
If window switching is implemented to handle transient and stationary portions, then transient response is improved, but device complexity increases due to signal analysis measures and decision steps
Solution Approach 1:
The patent applies self-service by designing a system where the window size automatically adapts based on the inherent characteristics of the input signal itself. The signal's own properties (such as energy distribution or spectral characteristics) drive the window size selection, eliminating the need for external signal analysis measures or decision steps. This self-adaptive mechanism reduces device complexity while maintaining good transient response.
3Speed
If window switching is used to adapt to signal characteristics, then transient performance is improved, but signal artifacts are introduced during switching
Solution Approach 1:
The patent applies dynamics by implementing smooth, continuous adaptation of window size rather than abrupt switching between fixed window sizes. This dynamic transition prevents sudden changes in signal processing characteristics that would cause artifacts. The window size evolves gradually based on signal characteristics, maintaining signal integrity while improving transient 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.