Time-Warped Audio Transform Coding Without Frame Discontinuities
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Solution Overview
Problem
Existing audio coding methods using time warping introduce discontinuities at frame borders and require significant bit-rate overhead for pitch variation parameters, leading to inefficiencies and audible distortions in encoding non-stationary signals.
Innovation Solution
Estimate a common time warp for consecutive audio frames to derive spectral representations, integrating time-warp operations with window functions for block transforms, allowing for efficient coding without audible discontinuities and reducing the need for pitch-related side information transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time warping is applied to encode non-stationary signals with pitch variation, then coding efficiency is improved, but discontinuities are introduced at frame borders and bit-rate overhead increases
Solution Approach 1:
The patent combines time-warp operations with window functions for block transforms, integrating two previously separate processing steps into a unified operation. This merging allows the time-warping to be applied continuously across frame boundaries rather than discontinuously at segment boundaries, eliminating audible discontinuities while maintaining coding efficiency for non-stationary signals with pitch variation.
2Stability of the object's composition
If simple time warping is applied to achieve constant pitch, then pitch variation is corrected, but uncontrollable duration violation and substantial bit-rate overhead occur
Solution Approach 1:
The patent changes the parameter representation from absolute tape speed to relative time-warp factors. Instead of transmitting absolute pitch or speed information that requires substantial bit-rate overhead, the system uses relative time-warp factors that describe pitch variation in a more compact form. This parameter transformation maintains pitch stability while significantly reducing the information that needs to be transmitted.
3Productivity
If large transform sizes are used for stationary signals, then coding gain is maximized, but the ability to handle non-stationary signals with pitch variation deteriorates
Solution Approach 1:
The patent introduces dynamic time-warping parameters that adapt to the local pitch variation characteristics of the signal. Instead of using a fixed transform size that must compromise between stationary and non-stationary signals, the system dynamically adjusts the time-warp factors to match the local pitch contour. This allows large transform sizes to be used for stationary segments (maximizing coding gain) while simultaneously adapting to handle non-stationary segments with pitch variation.
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.