Time-Warped Audio Transform Coding With Warp-Aware Windowing
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Solution Overview
Problem
Existing audio coding techniques face inefficiencies in encoding signals with pitch variations, leading to audible discontinuities and high bit-rate overhead due to uncontrollable duration and bandwidth limitations, especially in time-warped signals.
Innovation Solution
Estimating a common time warp for consecutive audio frames to derive window functions for overlap and add procedures, anticipating re-sampling and enabling efficient block-based transform coding without discontinuities, and reducing bit-rate demand by transmitting warp parameters instead of pitch information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time warping is applied to achieve constant pitch over voiced segments, then coding efficiency is improved, but absolute tape speed becomes uncontrollable leading to duration violation and bandwidth limitations
Solution Approach 1:
The patent applies preliminary time-warping to the audio signal before block transform coding, anticipating the pitch variations and correcting them in advance. This allows the subsequent transform coding to operate on a signal with more constant pitch, improving coding efficiency while the duration control is handled in the reconstruction stage
Solution Approach 2:
The patent changes the time parameter of the audio signal through time-warping operations, transforming the signal to have more constant pitch characteristics. This parameter transformation enables better coding efficiency by making the signal more stationary, while the original duration is preserved through proper reconstruction
2Productivity
If simple time warping is applied to achieve constant pitch, then coding efficiency is improved, but substantial bit-rate overhead is introduced for transmitting tape speed information
Solution Approach 1:
The patent extracts only the essential time-warping parameters needed for pitch correction, rather than transmitting complete tape speed information. By separating the pitch correction function from full speed control, the patent reduces the information that needs to be transmitted while maintaining the beneficial effects of time-warping
Solution Approach 2:
The patent introduces an intermediary time-warping operation that acts as a bridge between the original signal and the transform coding process. This intermediary transformation handles the pitch variations, allowing the main coding process to operate more efficiently without requiring extensive side information
3Productivity
If large transform sizes are used for stationary signals, then coding gain is maximized, but pitch variations cause scrambling of frequency analysis and quantization noise
Solution Approach 1:
The patent applies preliminary time-warping to correct pitch variations before the transform coding process. This pre-correction ensures that when large transform sizes are used, the frequency analysis is not scrambled by pitch variations, thereby maintaining both high coding gain and frequency analysis accuracy
Solution Approach 2:
The patent changes the time parameter of the signal through time-warping to compensate for pitch variations. This parameter transformation makes the signal more stationary within analysis frames, allowing large transform sizes to be used effectively without the harmful effects of pitch-induced frequency scrambling
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.