Time-Warped Transform Coding Across Audio Frames Without Discontinuities
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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 bit-rate overhead in time-warped signals.
Innovation Solution
A method that estimates a common time warp for consecutive audio frames, allowing for efficient block transform coding by integrating time-warp operations with window functions and resampling, thereby reducing audible discontinuities and bit-rate overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If simple time warping is applied to achieve constant pitch over voiced segments, then coding efficiency is improved, but duration of the encoded signal becomes uncontrollable and bandwidth limitations are violated
Solution Approach 1:
The audio signal is divided into consecutive non-overlapping frames, with each frame processed independently by time warping. This segmentation allows duration control at the frame level while maintaining overall signal structure, resolving the contradiction between coding efficiency and duration controllability.
Solution Approach 2:
The time warping operation is made dynamic and adaptive by estimating a common time warp parameter for each frame based on local pitch variation characteristics. This allows the system to apply time warping only where needed and at appropriate rates, maintaining duration control while improving coding efficiency in regions with pitch variation.
2Productivity
If common time warp is estimated for consecutive frames, then coding efficiency is improved, but bit-rate overhead increases due to additional side information transmission
Solution Approach 1:
The time warp parameter is quantized to a limited set of discrete values, reducing the number of bits required to transmit this side information. By changing the parameter representation from continuous to discrete with limited levels, the system achieves better coding efficiency while controlling bit-rate overhead.
Solution Approach 2:
The common time warp parameter estimated for consecutive frames is reused and copied across multiple frames rather than being independently transmitted for each frame. This reduces redundant information transmission and minimizes bit-rate overhead while maintaining coding efficiency benefits.
3Adaptability or versatility
If frame size is decreased to handle transient events, then adaptability to pitch variation is improved, but coding gain decreases rapidly
Solution Approach 1:
The system dynamically adapts the effective processing duration through time warping rather than reducing frame size. By warping the time axis to achieve constant pitch within frames, the system maintains large frame sizes for high coding gain while still adapting to local pitch variations, thus preserving coding efficiency.
Solution Approach 2:
Instead of changing the frame size parameter, the system changes the time scaling parameter through time warping. This allows the frame to cover the same time duration (maintaining coding gain) while transforming the signal to have constant pitch characteristics (improving adaptability to 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.