Audio Synthesis Filterbank With Asymmetric Windowing for Low Delay
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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 across these parameters.
Innovation Solution
The use of complex modulated low-delay filterbanks with asymmetric window functions that distribute energy across two portions of window coefficients, allowing for reduced delay or improved quality without increasing computational complexity, by employing analysis and synthesis filterbanks with specific window functions that extend the filter impulse response without introducing additional delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional filter banks with symmetric window functions are used, then reconstruction quality is maintained, but delay increases
Solution Approach 1:
The patent applies asymmetry by using asymmetric window functions where the first portion (earlier time coefficients) has higher energy than the second portion (later time coefficients). This asymmetric energy distribution allows the filter bank to achieve lower delay while maintaining reconstruction quality, as the higher energy in the first portion provides better signal representation earlier in time.
Solution Approach 2:
The patent changes the parameter distribution within the window function by allocating different energy levels to different portions of the window coefficients. Specifically, it modifies the energy distribution parameter such that the first portion has higher energy concentration, which directly impacts the delay characteristic while preserving reconstruction fidelity through proper parameter design.
2Manufacturing precision
If filter length is increased to improve reconstruction quality, then quality improves, but delay increases
Solution Approach 1:
The patent resolves this contradiction by changing the energy distribution parameters within the window function rather than simply increasing filter length. By concentrating higher energy in the first portion of the window coefficients, the system achieves better reconstruction quality with effective use of filter length, while the asymmetric distribution reduces the effective delay compared to symmetric distributions of the same length.
3Manufacturing precision
If bit rate is increased to improve audio quality, then quality improves, but transmission bandwidth increases
Solution Approach 1:
The patent optimizes the audio coding efficiency by changing the window function parameters to achieve better energy compaction and signal representation. The asymmetric window function with higher energy in the first portion improves the efficiency of the transform coding, allowing for better audio quality at lower bit rates by more effectively representing the signal characteristics in the transformed domain.
Data Source
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AI summary
An apparatus for generating time-domain audio samples or synthesis filterbank (300) comprises a calculator (310) for calculating a frame (330) comprising a sequence of intermediate time-domain samples from audio subband values of block (320). The calculator (310) is coupled to a synthesis windower (360) to which the frame (330) of intermediate time-domain samples is provided. The synthesis windower (360) is adapted to windowing the sequence of intermediate time-domain samples using a synthesis window function (370) and provides a frame (380) of windowed intermediate time-domain samples. The synthesis windower (360) is coupled to an overlap-adder output stage (400) that obtains a block (410) of time-domain samples. The block (410) of the time-domain (output) samples can then for instance be provided to further components for further processing, storing or transforming into audible audio signals.