Time-Warped Audio Transform Coding for Smooth Frame Reconstruction
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Solution Overview
Problem
Existing audio coding techniques face inefficiencies in encoding signals with pitch variations, leading to increased bit rates and audible discontinuities due to uncontrollable duration and bandwidth limitations in time-warped signals, as well as significant bit-rate overhead for transmitting pitch information.
Innovation Solution
A method for efficient audio coding using time warping, where a common time warp is estimated for consecutive frames to facilitate block transforms, allowing for overlap and add reconstruction without introducing rapid pitch variations at frame borders, and reducing the need for additional pitch information transmission by using warp parameters instead of pitch parameters.
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 uncontrollable duration and bandwidth limitations occur leading to violation of signal duration and bandwidth constraints
Solution Approach 1:
The patent changes the parameter representation from absolute pitch values to relative pitch ratios between adjacent frames. This allows the time-warping operation to maintain constant pitch within frames while the sequence of pitch ratios controls the overall pitch contour, thereby maintaining signal duration and bandwidth constraints while achieving coding efficiency.
Solution Approach 2:
The patent segments the signal processing into frame-level constant pitch transformation and inter-frame pitch ratio transmission. Each frame is processed independently with time-warping to achieve local stationarity, while the global duration and bandwidth constraints are maintained through controlled pitch ratio sequences between frames.
2Duration of action of moving object
If additional side information on tape speed (pitch) is transmitted to control duration, then signal duration is preserved, but substantial bit-rate overhead is introduced especially at low bit-rates
Solution Approach 1:
The patent transmits pitch ratios between adjacent frames instead of absolute pitch values or tape speed information. This parameter transformation reduces the bit-rate overhead because pitch ratios can be represented with fewer bits and exhibit better predictive coding properties, while still allowing accurate reconstruction of the signal duration.
3Duration of action of moving object
If consecutive non-overlapping segments are processed independently by time warp to preserve duration, then signal duration is maintained, but pitch jumps at segment boundaries introduce audible discontinuities and loss of coding efficiency
Solution Approach 1:
The patent applies time-warping transformation preliminarily within each frame to achieve local pitch stationarity before encoding. By processing overlapping or adjacent frames with continuous pitch ratio control, the harmful pitch jumps at boundaries are eliminated while maintaining signal duration through controlled pitch evolution between frames.
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.