Time-Warped Transform Coding With Overlap-Add Audio Reconstruction
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Solution Overview
Problem
Existing audio coding techniques face inefficiencies in encoding signals with pitch variations, leading to audible discontinuities and increased bit rate demands due to uncontrollable duration and bandwidth limitations, especially in time-warped signals.
Innovation Solution
Estimating a common time warp for consecutive audio frames to enable efficient block transform coding, integrating time-warp operations with window functions and resampling, thereby reducing audible discontinuities and bit rate overhead by transmitting warp parameters instead of pitch information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If simple time warping is applied to achieve constant pitch over voiced segments, then pitch stability is improved, but duration control deteriorates and bandwidth limitations are violated
Solution Approach 1:
The patent applies time warping by changing the time parameter of the audio signal to achieve constant pitch over voiced segments. A time warp function is applied to the input signal to transform the time axis, making the pitch stable during voiced portions while allowing flexible duration control through parameter adjustment
2Productivity
If frame-based transform coding is used for stationary signals, then coding efficiency is improved, but handling of non-stationary signals deteriorates
Solution Approach 1:
The patent makes the transform adaptive by dynamically adjusting the transform basis functions according to the signal's stationarity characteristics. The system switches between different transform types (DCT for stationary, DFT for transient) based on signal analysis, enabling both high coding efficiency for stationary segments and proper handling of non-stationary portions
3Measurement precision
If pitch information is transmitted to control time warping, then reconstruction accuracy is improved, but bit rate overhead increases substantially
Solution Approach 1:
The patent extracts only the essential time warp parameters needed for reconstruction rather than transmitting full pitch information. By taking out only the critical timing transformation parameters and discarding redundant pitch data, the system achieves accurate reconstruction with minimal bit rate overhead
4Productivity
If large transform sizes are used for stationary signals, then coding gain is improved, but resolution of transient events deteriorates
Solution Approach 1:
The patent segments the audio signal into stationary and transient portions, applying different transform sizes to each segment. Large transform sizes are used for stationary segments to maximize coding gain, while small transform sizes are used for transient segments to maintain temporal resolution, with smooth transitions between segments
Data Source
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AI summary
A spectral representation of an audio signal having consecutive audio frames can be derived more efficiently, when a common time warp is estimated for any two neighbouring frames, such that a following block transform can additionally use the warp information. Thus, window functions required for successful application of an overlap and add procedure during reconstruction can be derived and applied, the window functions already anticipating the re-sampling of the signal due to the time warping. Therefore, the increased efficiency of block-based transform coding of time-warped signals can be used without introducing audible discontinuities.