Asymmetric Audio Window Overlap for Low-Delay Transform Switching
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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 transitions, which often compromise frequency separation or increase coder delay.
Innovation Solution
The use of asymmetric transform windows with truncated overlap portions allows for flexible transform size switching without inserting additional transition windows, enabling efficient coding of both stationary and transient signals while maintaining reduced delay and perfect reconstruction properties.
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 from the audio processing chain, replacing it with a fixed low overlap approach. This eliminates the harmful element (transition window causing delay) while preserving the beneficial frequency separation through the fixed overlap mechanism.
Solution Approach 2:
The patent changes the overlap parameter from variable (transition windows) to fixed (low overlap for all transform sizes). This parameter change allows instant switching between transform sizes without requiring transition windows, thereby reducing coder delay while maintaining frequency separation through the fixed overlap value.
2Loss of time
If a fixed low window overlap is used for all transform sizes, then coder delay is reduced, but frequency separation deteriorates
Solution Approach 1:
The patent employs asymmetric MDCT windows where the analysis and synthesis windows have different characteristics. The analysis window uses a fixed low overlap to minimize delay, while the asymmetric window shape itself provides the frequency separation needed, compensating for the reduced overlap length.
3Loss of time
If asymmetric MDCT windows with shortened overlap are used, then coder delay is reduced, but frequency separation is compromised
Solution Approach 1:
The patent uses asymmetric MDCT windows where the window shape itself provides frequency separation compensation. The asymmetric design allows the window to maintain spectral resolution even with shortened overlap, as the non-symmetric shape creates different spectral leakage patterns that preserve frequency information.
Solution Approach 2:
The patent changes the window shape parameter from symmetric to asymmetric, which fundamentally alters the spectral characteristics. This parameter change allows the system to achieve both reduced delay (through shortened overlap) and maintained frequency separation (through the asymmetric window's spectral properties).
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.