Asymmetric Audio Window Switching With Truncated Overlap
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Solution Overview
Problem
Existing audio processing technologies face challenges in achieving low delay and high coding efficiency, particularly in handling transform size switching and window overlaps, which affect frequency separation and coder delay in audio coders.
Innovation Solution
The use of asymmetric transform windows with truncated overlap portions allows for flexible transform size switching without increasing coder delay, enabling efficient coding of both stationary and transient signals by constructing and applying windowed audio signal portions using a processor or method that determines and applies these windows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transition windows are inserted between frames encoded using different transform lengths, then frequency separation is improved, but coder delay increases
Solution Approach 1:
The patent extracts and removes the transition window portion from the frame structure, allowing instant switching between different transform lengths without requiring transition windows. This is achieved by using asymmetric analysis and synthesis windows where the analysis window extends beyond the frame boundary and the synthesis window compensates for this extension, enabling direct switching without intermediate transition frames.
Solution Approach 2:
The patent performs preliminary design of asymmetric windows where the analysis window shape is predetermined to extend beyond frame boundaries. This pre-planned window structure allows immediate switching between transform lengths without requiring runtime transition windows, as the windowing function itself provides the necessary smoothing and frequency separation.
2Loss of time
If low window overlap is used for all transform sizes, then coder delay is reduced, but frequency separation is degraded
Solution Approach 1:
The patent applies different overlap characteristics to different parts of the windowing function. The analysis window has a long tail extending beyond the frame boundary while the synthesis window has corresponding asymmetric structure. This local differentiation in window properties allows maintaining low overall overlap delay while providing sufficient frequency separation through the asymmetric window shapes.
Solution Approach 2:
The patent employs asymmetric analysis and synthesis windows where the window shapes are not symmetric around their centers. The analysis window extends further in one direction than the other, and the synthesis window is designed to complement this asymmetry. This asymmetric structure enables flexible overlap management that reduces delay while maintaining frequency separation.
3Measurement precision
If asymmetric MDCT windows with long overlap with previous frame are used, then frequency separation is improved, but look-ahead delay increases
Solution Approach 1:
The patent inverts the conventional approach by making the analysis window extend beyond the current frame boundary rather than requiring look-ahead. Instead of looking ahead to prepare transition windows, the analysis window naturally extends into the next frame, and the synthesis window compensates by having corresponding asymmetric structure. This inversion eliminates look-ahead delay while maintaining frequency separation.
Data Source
AI summary
A processor for processing an audio signal has: an analyzer for deriving a window control signal from the audio signal indicating a change from a first asymmetric window to a second window, or indicating a change from a third window to a fourth asymmetric window, wherein the second window is shorter than the first window, or wherein the third window is shorter than the fourth window; a window constructor for constructing the second window using a first overlap portion of the first asymmetric window, wherein the window constructor is configured to determine a first overlap portion of the second window using a truncated first overlap portion of the first asymmetric window, or wherein the window constructor is configured to calculate a second overlap portion of the third window using a truncated second overlap portion of the fourth asymmetric window; and a windower for applying the first and second windows or the third and fourth windows to obtain windowed audio signal portions.