Complex Audio Subband Filterbanks With Asymmetric Low-Delay Windows
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Solution Overview
Problem
Digital audio processing systems face challenges in balancing bit rate, computational complexity, memory requirements, quality, and delay, particularly in real-time applications, where compromises often need to be made between these parameters to achieve optimal performance.
Innovation Solution
The implementation of complex-valued low-delay filterbanks with asymmetric window functions that distribute energy differently across window coefficients, allowing for reduced delay and improved quality without increasing computational complexity or memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetric window functions are used in filterbanks, then the filterbank provides stable frequency response, but the system delay increases and reconstruction quality deteriorates
Solution Approach 1:
The patent applies asymmetry by using asymmetric window functions instead of conventional symmetric window functions in the filterbank. The asymmetric window function has different weighting distributions that allow for reduced group delay while maintaining frequency response stability. This directly addresses the contradiction by breaking the symmetry constraint that causes the delay-quality tradeoff.
Solution Approach 2:
The patent changes the parameter distribution within the window function by using different parameter sets for different frequency bands. Specifically, it employs parameter-dependent window functions where parameters such as decay rates and weighting factors are adjusted based on the subband index, allowing optimization of delay characteristics without sacrificing frequency response stability.
2Measurement precision
If longer filter lengths are used to improve frequency selectivity, then the time-frequency localization improves, but the system delay increases
Solution Approach 1:
The patent applies local quality by using different window function characteristics for different frequency regions. The asymmetric window functions are designed with locally optimized parameters that provide better time localization for high frequencies and better frequency localization for low frequencies, thereby improving overall time-frequency localization without uniformly increasing delay across all bands.
Solution Approach 2:
The patent introduces dynamics by making the window function parameters dependent on the subband index and frequency position. This allows the filterbank to adaptively adjust its characteristics across different frequency regions, achieving optimal time-frequency localization for each band while maintaining manageable system delay through the asymmetric design.
3Manufacturing precision
If higher bit rates are used to improve audio quality, then the reconstruction quality improves, but the transmission bandwidth and computational complexity increase
Solution Approach 1:
The patent changes parameters by using asymmetric window functions with optimized parameter sets that improve the efficiency of the transform domain representation. This allows for better audio quality at lower bit rates by improving the energy compaction and sparsity of the transformed signal, thereby reducing the computational complexity of encoding and decoding while maintaining or improving quality.
4Loss of time
If lower delay is achieved through asymmetric window functions, then the real-time performance improves, but the reconstruction quality may deteriorate
Solution Approach 1:
The patent uses asymmetry in the window function design to achieve lower group delay while maintaining reconstruction quality. The asymmetric weighting allows for faster decay of the impulse response, reducing delay, while the carefully designed parameter distribution ensures that the frequency response characteristics are preserved, thereby maintaining reconstruction quality despite the reduced symmetry.
Data Source
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AI summary
An embodiment of an apparatus (100) for generating audio subband values in audio subband channels comprises an analysis windower (110) for windowing a frame (120) of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function (190) comprising a sequence of window coefficients to obtain windowed samples. The analysis window function (190) comprises a first group (200) of window coefficients and a second group (210) of window coefficients. The first group (200) of window coefficients is used for windowing later time-domain samples and the second group (210) of window coefficients is used for windowing an earlier time-domain samples. The apparatus (100) further comprises a calculator (170) for calculating the audio subband values using the windowed samples.