Adaptive Audio Window Overlap for Transient Pre-Echo Control
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Solution Overview
Problem
Conventional audio coding systems face challenges in minimizing look-ahead delay while maintaining audio quality, particularly 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 adaptive selection of window overlap widths to minimize look-ahead delay and reduce pre-echo noise, by using a group of windows with varying overlap lengths, including zero overlap, to accurately capture transients without smearing coding errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a long transform with 50% overlap is used for stationary signals, then coding efficiency is improved, but transient signal quality deteriorates due to pre-echo and post-echo noise
Solution Approach 1:
The patent implements dynamic switching between different window overlap widths (50% for stationary signals, reduced overlap for transient signals) based on transient detection. This allows the system to adapt its parameters in real-time, using long transforms with full overlap during stationary periods for coding efficiency, and switching to shorter effective transforms with reduced overlap during transients to minimize pre-echo and post-echo artifacts
Solution Approach 2:
The patent changes the window overlap parameter from a fixed 50% to a variable parameter that can be reduced for transient signals. By modifying the overlap width parameter dynamically based on signal characteristics, the system optimizes the trade-off between coding efficiency and transient quality, reducing the time extension of transforms and their associated coding errors during transient periods
2Object-affected harmful factors
If transform switching is implemented to handle transient signals, then transient quality is improved, but look-ahead delay increases due to asymmetric transition windows
Solution Approach 1:
The patent employs asymmetric window functions (start window and stop window) that are optimized for different transition directions. The start window is designed for transitioning from long to short transforms, while the stop window handles the reverse transition. This asymmetric design allows for more efficient transition management, reducing the look-ahead delay required for transform switching while maintaining transient signal quality
Solution Approach 2:
The patent performs preliminary transient detection in a look-ahead region to identify upcoming transient signals before they occur in the main processing stream. By detecting transients in advance and preparing the appropriate window configuration, the system can switch transforms more efficiently with reduced delay, as the decision logic is already prepared based on the pre-analyzed transient characteristics
3Object-affected harmful factors
If reduced window overlap is used for transient signals, then pre-echo noise is reduced, but coding efficiency decreases due to shorter transform length
Solution Approach 1:
The patent segments the signal processing into different regions: stationary regions use long transforms with 50% overlap for high coding efficiency, while transient regions use reduced overlap to minimize pre-echo noise. By segmenting the signal based on transient detection and applying different window overlap parameters to different segments, the system optimizes both coding efficiency and transient quality without compromising overall performance
Solution Approach 2:
The patent applies different window overlap parameters locally based on the signal characteristics. Instead of using a uniform overlap width throughout, the system adjusts the overlap parameter locally around transient regions where it is needed most, while maintaining full 50% overlap in stationary regions for optimal coding efficiency. This localized parameter adjustment minimizes pre-echo noise precisely where it occurs without sacrificing overall coding performance
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.