Active Noise Reduction Filter Control for Fast Stable Convergence
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Solution Overview
Problem
Conventional active noise reduction devices face challenges in quickly converging filter coefficients due to small step-size parameters, leading to delayed noise reduction and instability, especially when noise levels change frequently during vehicle operation.
Innovation Solution
The active noise reduction device incorporates a μ-adjustment unit that dynamically calculates the step-size parameter based on representative input values and standard values, allowing for optimal convergence and stability of filter coefficients, even with large reference signals, by multiplying a standard step-size parameter by a ratio of current to standard representative input values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small step-size parameter is used to ensure stability of filter coefficient convergence, then the filter coefficient converges stably, but the converging speed becomes slow and noise reduction is delayed
Solution Approach 1:
The patent applies dynamics by making the step-size parameter variable rather than fixed. The μ-adjustment unit dynamically adjusts the step-size parameter based on the current noise level and convergence state, allowing the system to transition between different operational modes: using larger step-sizes for faster convergence when far from optimal, and smaller step-sizes for stable refinement when near convergence, thus resolving the contradiction between stability and speed
Solution Approach 2:
The patent changes the parameter μ (step-size parameter) based on the representative input value and convergence progress. By computing μ as a function of the ratio between standard representative input value and current representative input value, the system adapts the step-size parameter to match current operating conditions, achieving both fast initial convergence and stable final convergence without the trade-off present in fixed-parameter systems
2Speed
If a large step-size parameter is used to increase converging speed, then the filter coefficient converges quickly, but the system becomes unstable and the filter coefficient may diverge
Solution Approach 1:
The patent implements feedback by continuously monitoring the representative input value and using it to adjust the step-size parameter μ in real-time. The μ-adjustment unit receives feedback about the current convergence state and noise characteristics, and adjusts μ accordingly to maintain stability while maximizing convergence speed, preventing the divergence that occurs with fixed large step-sizes
3Reliability
If the step-size parameter is fixed to ensure stability, then the filter coefficient converges stably, but the system cannot adapt to frequently changing noise conditions
Solution Approach 1:
The patent makes the step-size parameter dynamic and adaptive to changing conditions. The μ-adjustment unit continuously updates μ based on the representative input value that reflects current noise characteristics, allowing the system to adapt to frequently changing noise conditions while maintaining stability through controlled adjustment of the step-size parameter
Solution Approach 2:
The patent changes the step-size parameter μ in response to changing noise conditions by computing it as a function of the representative input value. This allows the system to adapt its convergence behavior to match current operating conditions, achieving both stability and adaptability that are impossible with fixed parameters
Data Source
AI summary
An active noise reduction device is used with a secondary noise source that generates a secondary noise and an error signal source that outputs an error signal corresponding to a residual sound caused by interference between the secondary noise and a noise. A μ-adjustment unit calculates a step-size parameter for updating a filter coefficient of an adaptive filter by multiplying a standard step-size parameter by a ratio of a standard representative input value corresponding to amplitude of a signal to a representative input value corresponding to the amplitude of the signal.