Active Noise Control Device Adaptive Filter Coefficient Update
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Solution Overview
Problem
Existing active noise control devices face challenges in maintaining effective noise reduction when the transfer characteristic between the speaker and microphone changes, leading to potential noise amplification and abnormal noise occurrences.
Innovation Solution
An active noise control device that employs adaptive notch filters and a secondary path filter coefficient updating mechanism, using an initial value table and updated value table to store and update filter coefficients, allowing the system to adapt to changes in the transfer characteristic without pre-measurement, ensuring continuous noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the transfer characteristic is measured in advance and used as correction values, then the initial noise reduction performance is improved, but the system cannot adapt when the transfer characteristic changes
Solution Approach 1:
The patent implements dynamic adaptation by continuously updating the secondary path filter coefficients using adaptive algorithms (NLMS, FxLMS). The system transitions from static pre-measured correction values to dynamic real-time coefficient adjustment, allowing the filter to track changes in transfer characteristics between the speaker and microphone.
Solution Approach 2:
The system performs self-calibration by automatically updating its own filter coefficients based on error signals from the microphone. The adaptive algorithm uses the difference between expected and actual acoustic responses to self-correct the transfer characteristic estimation without external intervention.
2Adaptability or versatility
If adaptive filtering is used to update based on error signals, then adaptability to changes is improved, but the system may diverge or produce abnormal noise when transfer characteristics change
Solution Approach 1:
The system employs feedback mechanisms where the microphone captures the actual acoustic response, converts it to an error signal, and feeds this back to the adaptive filter. This closed-loop feedback allows the system to continuously monitor and adjust to transfer characteristic changes while maintaining stability through controlled adaptation.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting filter coefficients based on operating conditions. The system monitors error signal magnitudes and adapts coefficient update rates, allowing it to respond to transfer characteristic changes while preventing divergence through controlled parameter adjustment.
3Measurement precision
If multiple virtual error signals are generated and multiple filter coefficient updates are performed, then noise reduction performance is improved, but the device complexity increases
Solution Approach 1:
The patent segments the noise control task into multiple parallel adaptive filter updates: one for the control filter coefficients and another for the secondary path filter coefficients. Each filter type processes specific error signals independently, dividing the complex adaptation task into manageable segments that can be computed in parallel.
Solution Approach 2:
The system merges multiple signal processing paths by combining the control filter output with secondary path filter output to generate comprehensive error signals. Multiple virtual error signals from different processing paths are combined and used together to drive the adaptive coefficient updates, achieving enhanced noise reduction through integrated processing.
Data Source
AI summary
An active noise control device includes an updated value table operating unit that writes initial values of an initial value table into an updated value table as updated values and writes updated coefficients of a secondary path filter C{circumflex over ( )} updated in a secondary path filter coefficient updating unit during active noise control, into the updated value table as updated values. The secondary path filter coefficient updating unit reads the updated value corresponding to a frequency from the updated value table before updating the coefficients of the secondary path filter C{circumflex over ( )}, and updates the coefficients of the secondary path filter C{circumflex over ( )}, using the read updated values as the pervious values.