Asymmetric Audio Window Overlap Switching for Low-Delay Coding
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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.
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 truncated overlap portions.
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 only the necessary overlap portion from the asymmetric window and discards the remaining part. By taking out only the essential overlap samples needed for frequency separation and discarding the rest, the solution achieves good frequency separation without requiring full transition windows, thus reducing coder delay while maintaining spectral accuracy.
Solution Approach 2:
The patent segments the asymmetric window into two parts: the overlap portion that is retained and the remaining portion that is discarded. This segmentation allows the system to use only the critical part of the window for frequency separation while eliminating the parts that would increase delay, resolving the contradiction between frequency separation and coder delay.
2Loss of time
If low window overlap is used for all transform sizes, then coder delay is reduced, but frequency separation deteriorates
Solution Approach 1:
The patent applies different overlap strategies to different parts of the windowing function. Specifically, it uses a longer overlap portion from the asymmetric window where it is most needed for frequency separation, while using shorter overlap elsewhere. This local differentiation of overlap quality achieves good frequency separation without uniformly increasing coder delay across all transform sizes.
Solution Approach 2:
The patent changes the overlap parameter dynamically based on the window type and transform size. Instead of using a fixed low overlap for all cases, it adjusts the overlap length by selecting appropriate portions from asymmetric windows, thereby optimizing frequency separation for each specific transform size without proportionally increasing coder delay.
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 extracts only the necessary overlap portion from the asymmetric window that provides frequency separation benefits, while discarding the portions that would increase look-ahead delay. By taking out only the essential overlap samples and discarding the rest, the system achieves good frequency separation without requiring the full long overlap of traditional asymmetric windows.
Solution Approach 2:
The patent applies partial overlap rather than full overlap from the asymmetric window. By using only the necessary portion of the overlap (partial action) rather than the complete overlap designed for optimal frequency separation, the system achieves sufficient frequency separation with reduced look-ahead delay, avoiding the excessive delay that would result from implementing the full asymmetric window overlap.
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.