Adaptive Filter Stability for Overlapping Harmonic Noise
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Solution Overview
Problem
Adaptive feed-forward noise reduction systems face instability and noise artifacts when canceling frequencies that are close or coincident, particularly in motor vehicles where engine and propeller shaft harmonics are involved, leading to compromised stability margins and potential divergence of filter algorithms.
Innovation Solution
The system employs an overlap detector to assess the proximity of frequencies being canceled, allowing adjustments to adaptive filter parameters such as adaptation step size and leakage to maintain stability margins, ensuring effective cancellation by altering the operation of adaptive filters when frequencies overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two or more adaptive filters are used to cancel noise from multiple sources (engine and propeller shaft), then the system can cancel a broader range of noise frequencies, but the stability margins of the filters are compromised and divergence becomes more likely
Solution Approach 1:
The system dynamically adjusts the adaptation step size of adaptive filters based on the frequency proximity between multiple noise sources. When frequencies are close, the adaptation step size is reduced to maintain stability; when frequencies are well-separated, the adaptation step size can be increased for faster convergence. This dynamic parameter adjustment allows the system to maintain both multi-source cancellation capability and filter stability.
Solution Approach 2:
The patent changes key parameters of the adaptive filter algorithm (adaptation step size, leakage factor) based on the detected frequency proximity of multiple noise sources. By monitoring the frequency separation between engine harmonics and propeller shaft harmonics, the system adjusts these parameters to prevent divergence while maintaining effective noise cancellation across multiple sources.
2Reliability
If adaptive filter parameters are adjusted to maintain stability when frequencies are close, then system divergence is reduced, but the complexity of the noise reduction system increases
Solution Approach 1:
The system implements a feedback mechanism where the frequency proximity between multiple noise sources is continuously monitored, and based on this information, the adaptation parameters of the filters are automatically adjusted. This closed-loop control ensures stability without requiring complex manual tuning or additional hardware, as the system self-regulates based on real-time frequency analysis.
Solution Approach 2:
The noise reduction system performs self-adjustment by automatically detecting frequency proximity and modifying its own filter parameters accordingly. The system serves itself by implementing stability control through autonomous parameter adaptation, eliminating the need for external intervention or complex control mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes the likelihood of system divergence and reduces detectable noise artifacts, maintaining performance similar to single-canceller systems even when frequencies are close, thereby enhancing the stability and effectiveness of harmonic noise cancellation.
Implementation Method 1
The adaptive filter can alter the magnitude and/or the phase of the input sine wave. The output of the adaptive filter is applied to one or more transducers that produce sound (i.e., loudspeakers) that is acoustically opposite to the undesirable engine harmonics
Implementation Method 2
The output of the adaptive filter is applied to one or more transducers that produce sound (i.e., loudspeakers) that is acoustically opposite to the undesirable engine harmonics that are to be canceled
Implementation Method 3
Engine harmonic cancellation systems also use one or more microphones as error input transducers
Data Source
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AI summary
A system and method for reducing harmonic noise caused by two or more noise sources by causing one or more loudspeakers to produce sounds that are at about the same frequencies as the noise and of substantially opposite phase. There is a noise canceller associated with each noise source. Each noise canceller includes a harmonic sine wave generator that generates an output sine wave. Each noise canceller also has an adaptive filter that uses a sine wave to create a noise reduction signal that is used to drive one or more transducers with their outputs directed to reduce noise caused by the noise sources. There is an overlap detector that compares the harmonic frequencies and, based on their proximity, alters the operation of one or more adaptive filters.