Asymmetric Overlap Windows for Low-Delay Audio Transform Coding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing audio coding techniques face challenges in reducing algorithmic delay while maintaining audio quality, particularly when using asymmetric windows, which can lead to audible degradation due to high weighting values exceeding 1, complicating fixed-point implementation and frequency selectivity.
Innovation Solution
A method for coding digital audio signals using asymmetrical weighting windows with four distinct portions: increasing, constant at 1, decreasing, and constant at 0, optimized to reduce complexity and improve audio quality by adjusting the intervals based on the desired delay and block duration, ensuring efficient implementation and perfect reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If asymmetric windows with zeros at the tail of the analysis window are used to reduce delay, then algorithmic delay is reduced, but weighting values exceed 1 causing audible degradation and implementation complexity
Solution Approach 1:
The patent modifies the window function parameters by introducing a constant section at value 1 between the increasing and decreasing portions, and setting the tail portion to 0. This parameter change ensures weighting values stay within [0,1] range while maintaining delay reduction benefits of asymmetric windows.
Solution Approach 2:
The patent employs asymmetric windowing where the analysis window has zeros only at the tail (not symmetric at both ends), creating unequal distribution of window portions. This asymmetry reduces algorithmic delay while the controlled parameter ranges prevent implementation issues.
2Loss of time
If asymmetric windows are used to reduce delay, then algorithmic delay is reduced, but frequency selectivity deteriorates compared to symmetric windows
Solution Approach 1:
The patent applies different window characteristics to different portions of the signal: the increasing portion handles signal onset, the constant portion maintains steady-state with optimal weighting, and the decreasing portion handles signal decay. This local differentiation maintains frequency selectivity while achieving delay reduction.
3Loss of time
If weighting values exceed 1 in asymmetric windows, then delay reduction is achieved, but audio quality degrades due to high weighting values
Solution Approach 1:
The patent constrains the weighting function parameters so that values remain within the [0,1] range by introducing the constant section at value 1 and setting the tail to 0. This prevents the weighting values from exceeding 1, thereby maintaining audio quality while still achieving delay reduction through the asymmetric structure.
Data Source
Figure 1~3
Figure 4~6
Figure 7
AI summary
The invention relates to the coding/decoding of a digital signal, consisting of successive blocks of samples, the coding being of the transform with overlap type and comprising, upon analysis, the application of a weighting window to two blocks of M successive samples. In particular, this weighting window is asymmetric and comprises four distinct portions extending successively over the two aforesaid blocks, with: a first portion (wl), increasing over a first interval of samples, a second portion (w2), constant at a value of 1 over a second interval, a third portion (w3), decreasing over a third interval, and a fourth portion (w4), constant at a value of 0 over a fourth interval.