Transient-Location Window Overlap for Low-Delay Audio Encoding
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Solution Overview
Problem
Conventional audio coding systems face challenges in minimizing look-ahead delay while maintaining audio 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 apparatus and method for encoding and decoding audio signals that utilize a controllable windower to apply specific overlap lengths based on transient locations, allowing for flexible selection among multiple overlap widths to minimize look-ahead delay and reduce pre-echo noise, by using a transient location detector to identify transient positions within frames and adjust window overlap accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional audio coding systems use fixed window lengths and transform switching, then coding simplicity is maintained, but look-ahead delay increases and pre-echo noise occurs
Solution Approach 1:
The patent implements dynamic adjustment of window overlap lengths based on transient detection. The system transitions from fixed window lengths to variable overlap lengths (50%, 25%, 0%) selected according to transient characteristics, allowing the coding system to adapt its parameters in real-time to minimize look-ahead delay while maintaining audio quality
Solution Approach 2:
The patent changes the parameter of window overlap length from a fixed value to a variable parameter with at least three different lengths. This parameter change enables the system to optimize look-ahead delay by selecting appropriate overlap lengths based on transient detection results, directly addressing the time loss issue
2Manufacturing precision
If asymmetric transition windows are used for transform switching, then transient coding accuracy is improved, but device complexity and look-ahead requirements increase
Solution Approach 1:
The patent applies different window overlap lengths to different signal segments based on transient detection. By identifying transient locations and applying appropriate overlap lengths (50% for stationary, 25% for transition, 0% for transient regions), the system achieves high transient coding accuracy while avoiding the complexity of asymmetric transition windows throughout the entire signal
Solution Approach 2:
The patent segments the audio signal processing into different regions (stationary, transition, transient) and applies different window overlap strategies to each segment. This segmentation allows the system to achieve high transient coding accuracy in critical regions while using simpler methods in stationary regions, reducing overall device complexity
3Reliability
If reduced window overlap is used for non-stationary signals, then temporal spread of coding error is minimized, but audio quality during stationary passages deteriorates
Solution Approach 1:
The patent dynamically selects window overlap lengths based on signal stationarity detection. The system uses 50% overlap for stationary passages to maintain audio quality, switches to 25% or 0% overlap for non-stationary and transient regions to minimize coding error temporal spread, thus achieving both reliability and quality through adaptive parameter control
Data Source
AI summary
An apparatus for encoding an audio or image signal, includes: a controllable windower for windowing the audio or image signal to provide the sequence of blocks of windowed samples; a converter for converting the sequence of blocks of windowed samples into a spectral representation including a sequence of frames of spectral values; a transient location detector for identifying a location of a transient within a transient look-ahead region of a frame; and a controller for controlling the controllable windower to apply a specific window having a specified overlap length to the audio or image signal in response to an identified location of the transient, wherein the controller is configured to select the specific window from a group of at least three windows, wherein the specific window is selected based on the transient location.