Active Noise Reduction Controller with Adaptive Secondary Path Filter
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Solution Overview
Problem
Existing active noise reduction systems fail to effectively adapt to changes in the user's position and the transfer function of the secondary path, leading to reduced noise reduction efficiency.
Innovation Solution
The system incorporates a controller with a control filter, a secondary path filter, and a correction filter that estimates the transfer function of the secondary path and adapts to changes, enhancing noise reduction control by correcting error signals and updating filters based on acoustic characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system uses a fixed secondary path filter without adaptive updating, then the device complexity is reduced, but the noise reduction effect deteriorates when the transfer function of the secondary path changes
Solution Approach 1:
The secondary path filter is transformed from a fixed configuration to a dynamic adaptive filter that automatically updates its parameters based on real-time acoustic environment changes. The controller continuously adjusts the filter coefficients to track variations in the secondary path transfer function, ensuring optimal noise reduction performance without requiring manual intervention or complex hardware modifications.
Solution Approach 2:
The system implements a feedback mechanism where the controller monitors the error signal and uses it to adaptively update the secondary path filter. By feeding back the difference between the actual and expected error signals, the system automatically adjusts the filter parameters to compensate for changes in the acoustic environment, maintaining high noise reduction effectiveness.
2Measurement precision
If the system only corrects error signals based on user position without adapting to secondary path changes, then the device complexity is reduced, but the noise reduction control accuracy deteriorates
Solution Approach 1:
The correction mechanism is divided into two independent but coordinated components: a correction filter that compensates for acoustic characteristics differences based on user position, and an adaptive secondary path filter that tracks transfer function changes. This segmentation allows each component to specialize in one aspect of adaptation, improving overall control accuracy while maintaining manageable system complexity.
Solution Approach 2:
The system merges the correction filter output with the adaptive secondary path filter output to generate the final control signal. By combining both correction mechanisms in the control loop, the system achieves comprehensive noise reduction control that accounts for both user position variations and secondary path changes, resulting in superior noise reduction accuracy.
Data Source
AI summary
An active noise reduction system includes an error microphone configured to generate an error signal, and a controller configured to control a speaker based on the error signal. The controller includes a control filter configured to generate a control signal, a secondary path filter that represents an estimation value of a transfer function of a secondary path, and a correction filter that represents a difference between acoustic characteristics at a position of the error microphone and acoustic characteristics at a position of a user. The controller is configured to generate a correction signal by the correction filter, generate a correction error signal by correcting the error signal using the correction signal, generate a canceling sound estimation signal by the secondary path filter based on the control signal, and adaptively update the secondary path filter based on the canceling sound estimation signal and the correction error signal.