Warp-Aware Audio Transform Coding for Pitch-Varying Frames
Find Innovative SolutionsGenerate Solutions
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 bit-rate overhead in time-warped signals, especially in cases of non-stationary audio like voiced sounds and musical instruments.
Innovation Solution
The implementation of a time-warped transform coding method that uses normalized warp maps and biorthogonal bases to maintain constant pitch within frames, allowing for efficient encoding and decoding without loss of information, by resampling and windowing the signal to align with the warp parameters, thereby reducing computational complexity and bit-rate overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time warping is applied to maintain constant pitch within frames, then coding efficiency is improved, but duration of the encoded signal becomes uncontrollable and bandwidth limitations are violated
Solution Approach 1:
The signal is divided into overlapping frames with a specific overlap ratio (e.g., 50%). Each frame is processed independently with time warping to maintain constant pitch, while the overlap ensures continuity. This segmentation allows local pitch correction without affecting the global duration control.
Solution Approach 2:
A normalization step is introduced as an intermediary process that scales the warped frame to match the original frame duration. This mediator ensures that while pitch is corrected within the frame, the overall signal duration remains controlled and bandwidth limitations are not violated.
2Stability of the object's composition
If simple time warping is applied to achieve constant pitch, then pitch variation is corrected, but additional side information on tape speed must be transmitted introducing substantial bit-rate overhead
Solution Approach 1:
Instead of transmitting absolute pitch or tape speed information, the invention changes the parameter to transmit only the warp factor (a normalization coefficient). This warp factor is derived from the ratio of original frame duration to warped frame duration, requiring significantly fewer bits while maintaining pitch stability.
Solution Approach 2:
The time warping is applied locally within each frame independently, allowing pitch correction to be achieved frame-by-frame without requiring global pitch information. This local approach reduces the amount of side information needed, as only local normalization factors must be transmitted rather than global pitch curves.
3Adaptability or versatility
If frame size is decreased to handle transient events, then adaptability to non-stationary signals is improved, but coding gain decreases rapidly
Solution Approach 1:
The invention introduces dynamic frame sizing through overlapping analysis frames with different effective durations. While the nominal frame size remains constant for transform coding, the overlapping structure and selective processing allow the system to adapt to transient events by applying time warping only where pitch variation occurs, maintaining large frame sizes for stationary parts to preserve coding gain.
Solution Approach 2:
The transform size parameter is kept large for stationary signal portions to maintain high coding gain, while the warp factor parameter dynamically adjusts the effective processing duration for transient portions. This separation allows the system to maintain large transform sizes overall while still adapting to transient events through localized parameter modification.
Data Source
Figure 1
Figure 2~2B
Figure 3A~3B
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.