Harmonic Transposition with Adaptive Windows for Clean 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, often requiring complex signal analysis and window switching, which can introduce artifacts.
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 window switching, ensuring minimal additional complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency resolution is used for stationary signal transposition, then transposition quality is improved, but 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 method automatically adjusts window length based on signal characteristics - using long windows for stationary portions to achieve high frequency resolution, and short windows for transient portions to maintain good transient response. This dynamic adaptation eliminates the need for manual window switching and associated artifacts.
2Measurement precision
If window switching is used to adapt to signal characteristics, then both frequency resolution and transient response are improved, but system complexity increases due to signal analysis and decision steps
Solution Approach 1:
The patent implements self-service by designing a transposition system that automatically adapts to signal characteristics without external control. The method inherently detects transient conditions through the transposition process itself and adjusts window size accordingly, eliminating the need for separate signal analysis modules and decision-making logic that would increase system complexity.
3Measurement precision
If window switching is implemented for adaptive transposition, then transposition quality is improved, but signal artifacts are introduced during window transitions
Solution Approach 1:
The patent eliminates window switching artifacts by implementing smooth dynamic adaptation of window size. Rather than abruptly switching between fixed window lengths, the system continuously adjusts window parameters based on signal characteristics, ensuring seamless transitions that do not introduce audible artifacts while maintaining optimal frequency resolution and transient response.
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.