Variable Bandwidth Delayless Subband Algorithm for Active Noise Control
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Solution Overview
Problem
Active noise control systems face challenges with high computational burden and slow convergence due to large reference signal eigenvalue spread, particularly in controlling broadband road noise, and suffer from aliasing effects in uniform discrete Fourier transform filter banks.
Innovation Solution
A variable bandwidth delayless subband algorithm is introduced, which decomposes signals into subbands with a filter bank design that minimizes aliasing and reduces computational complexity, using a discrete Fourier transform filter bank with offset center frequencies and variable bandwidths to overcome these limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a uniform discrete Fourier transform filter bank is used in the delayless subband algorithm, then the signal decomposition is simplified, but aliasing effects occur between adjacent subbands that degrade system performance
Solution Approach 1:
The patent applies local quality by making the filter bank bandwidths non-uniform across different subbands. Specifically, the bandwidth of each subband filter is adjusted according to the local spectral characteristics of the road noise, with narrower bandwidths in frequency regions where aliasing is more problematic and wider bandwidths where it is less critical. This localized adaptation resolves the contradiction by maintaining simple filter bank structure while eliminating aliasing effects through targeted bandwidth adjustment.
2Adaptability or versatility
If broadband white noise reference signal is used for road noise control, then the coverage frequency range is improved, but computational burden and convergence speed are degraded due to large reference signal eigenvalue spread
Solution Approach 1:
The patent applies segmentation by dividing the broadband reference signal into multiple narrowband subband signals using the non-uniform filter bank. Each subband signal has a smaller eigenvalue spread, which enables faster convergence of the adaptive noise control algorithm in each subband. The overall system achieves broadband coverage by combining the results from all subbands, thus resolving the contradiction between frequency range coverage and convergence speed.
3Reliability
If the bandwidth of the discrete Fourier transform filter bank is reduced to minimize aliasing, then aliasing effects are decreased, but the frequency resolution and coverage are compromised
Solution Approach 1:
The patent applies dynamics by making the filter bank bandwidths adjustable and adaptive rather than fixed. The bandwidth of each subband filter is dynamically adjusted based on the spectral characteristics of the input signal and the required aliasing performance. This allows the system to optimize the trade-off between aliasing reduction and frequency resolution by allocating narrower bandwidths where aliasing is critical and wider bandwidths where frequency resolution is more important.
Data Source
AI summary
An active noise control (ANC) system includes a speaker and one or more processors programmed to implement a delayless subband filtered-x least mean square control algorithm. The algorithm includes a variable bandwidth discrete Fourier transform filter bank having a number of subbands such that the system, in response to a broadband white noise reference signal indicative of road noise in the vehicle, exhibits a uniform gain spectrum across a frequency range defined by the subbands and partially cancels the road noise via output of the speaker.