Active Noise Reduction Using Precomputed Secondary Path Lookup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Active noise control systems face challenges when the distance between the control loudspeaker and the error microphone is large, leading to a slow update rate and potential divergence of the control filter due to long secondary path delays, making it difficult to efficiently reduce noise effectively.
Innovation Solution
The introduction of a processed secondary path characteristic, which shortens the delay in the secondary path characteristic by a time corresponding to the period of the target sound multiplied by a constant, allows for a higher update rate and minimizes the error signal, thereby relaxing the constraint of the slow adaptation limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the distance between control loudspeaker and error microphone is made long, then the spatial coverage and adaptability of the system is improved, but the secondary path delay increases causing slow update rate and potential filter divergence
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the processed secondary path characteristic in a lookup table during system initialization or calibration phase. This pre-processing step eliminates the need for real-time computation of the processed secondary path characteristic, allowing the system to handle long distances between loudspeaker and microphone without suffering from slow update rates or filter divergence.
2Reliability
If the update rate of control filter is reduced, then the filter stability is improved, but the time needed to generate control effect increases
Solution Approach 1:
The patent applies preliminary action by pre-computing the processed secondary path characteristic and storing it in a lookup table during system initialization. This eliminates the need for real-time computation of the processed secondary path characteristic, allowing the control filter to operate at higher update rates without causing divergence, thus reducing the time needed to generate control effect while maintaining stability.
Solution Approach 2:
The patent applies copying by creating a lookup table that stores pre-computed values of the processed secondary path characteristic. Instead of computing the processed secondary path characteristic in real-time during operation, the system copies pre-computed values from the lookup table, significantly reducing computational delay and enabling faster update rates.
3Length of stationary object
If the secondary path delay is long, then the system can handle larger distances between components, but the adaptation speed decreases
Solution Approach 1:
The patent applies preliminary action by pre-calculating the processed secondary path characteristic during system initialization or calibration, and storing it in a lookup table. This pre-computation step allows the system to handle long distances between components without suffering from slow adaptation speed, as the processed secondary path characteristic is readily available during operation without requiring real-time computation.
Solution Approach 2:
The patent applies copying by creating a lookup table that stores pre-computed values of the processed secondary path characteristic. This allows the system to quickly access and use the processed secondary path characteristic during operation, maintaining fast adaptation speed even when the distance between components is large.
Data Source
AI summary
According to an embodiment, an active noise-reduction apparatus includes following elements. The microphone converts a sound including a target sound into an error signal. The control filter generates a control signal in accordance with a control characteristic. The first control effect estimation filter converts the control signal into a first signal in accordance with an estimated secondary path characteristic. The second control effect estimation filter converts the control signal into a second signal in accordance with a processed secondary path characteristic obtained by shortening a delay of the estimated secondary path characteristic. The updating unit updates the control characteristic based on the error signal, the first signal, and the second signal.