Transient-Dependent Audio Window Overlap for Low-Look-Ahead Coding
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Solution Overview
Problem
Existing audio coding systems face challenges in minimizing look-ahead delay while maintaining coding quality, especially during transient signal segments, due to restricted window lengths and inefficiencies in transform switching, leading to pre-echo and post-echo noise.
Innovation Solution
An adaptive window selection mechanism that identifies transient locations within frames to choose from a set of overlapping windows with varying lengths, allowing for precise adaptation of transform lengths and overlap widths to minimize pre-echoes and artifacts, and a modified transition window with a 'double-overlap' region to reduce encoder look-ahead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asymmetric transition windows are used for transform switching, then transform length switching can be performed, but encoder look-ahead delay increases
Solution Approach 1:
The patent applies preliminary action by performing transform switching without requiring asymmetric transition windows, thereby eliminating the need for encoder look-ahead. The method switches between long and short transforms by adjusting the overlap region in the time domain, allowing immediate response to transient signals without delaying the encoding process.
Solution Approach 2:
The patent implements dynamics by making the overlap region width variable depending on the signal characteristics. The overlap width is dynamically adjusted between different values (e.g., first overlap width for normal operation, second overlap width for transient handling) based on the detected signal properties, enabling adaptive transform switching without fixed asymmetric windows.
2Reliability
If reduced overlap width is used for non-stationary signals, then temporal spread of coding error is minimized, but coding efficiency for stationary signals decreases
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the overlap width based on the detected signal characteristics. For non-stationary signals containing transients, a reduced overlap width is used to confine temporal spread of coding errors. For stationary signals, a larger overlap width is used to maintain coding efficiency. This dynamic adaptation allows the system to optimize both reliability and productivity according to signal conditions.
Solution Approach 2:
The patent implements parameter changes by varying the overlap width parameter according to signal characteristics. The system detects whether the signal is stationary or non-stationary and changes the overlap width parameter accordingly, thereby achieving both reduced temporal error spread for transients and maintained coding efficiency for stationary portions.
3Device complexity
If fixed window lengths are used, then implementation is simplified, but adaptability to transient and non-transient signal portions is limited
Solution Approach 1:
The patent applies dynamics by implementing variable window lengths that adapt to signal characteristics. Instead of using fixed window lengths, the system dynamically selects between different window lengths (corresponding to different overlap widths) based on whether the signal is stationary or contains transients. This maintains relative implementation simplicity while significantly improving adaptability.
Solution Approach 2:
The patent implements segmentation by dividing the signal processing into different segments with different window characteristics. The system segments the signal based on detected transients and applies appropriate window lengths to different segments - longer windows for stationary portions and shorter windows for transient portions, thereby achieving adaptability while maintaining manageable complexity.
Data Source
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AI summary
An apparatus for encoding an audio or image signal, comprises: a controllable windower (102) for windowing the audio or image signal to provide the sequence of blocks of windowed samples; a converter (104) for converting the sequence of blocks of windowed samples into a spectral representation comprising a sequence of frames of spectral values; a transient location detector (106) for identifying a location of a transient within a transient look-ahead region of a frame; and a controller (108) for controlling the controllable windower (102) to apply a specific window having a specified overlap length to the audio or image signal in response to an identified location (210-213) of the transient, wherein the controller (108) is configured to select the specific window from a group of at least three windows comprising a first window (201) having a first overlap length (203), a second window (215) having a second overlap length (218), and a third window (224) having a third overlap length (229) or having no overlap, wherein the first overlap length (203) is greater than the second overlap length (218), and wherein the second overlap length (218) is greater than the third overlap length (229) or greater than an overlap of zero, wherein the specific window is selected based on the transient location such that one of two time-adjacent overlapping windows has coefficients at the location of the transient and the other of the two time-adjacent overlapping windows has second window coefficients at the location of the transient, wherein the second coefficients are at least nine times greater than the first coefficients.