Adaptive ANC Filter Updates for Stable Personal Audio
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Solution Overview
Problem
Adaptive noise canceling circuits in personal audio devices can generate undesirable responses and instability due to external changes in the acoustic environment, such as varying noise sources and device position.
Innovation Solution
A personal audio device with an integrated circuit that includes a microphone to measure ambient audio, generating an anti-noise signal using adaptive filters, which adjusts its coefficients based on an error signal. The system modifies the cost function to prevent instability by ceasing updates when the error signal magnitude exceeds a threshold, ensuring robust noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If adaptive noise canceling circuits continuously update filter coefficients to adapt to environmental changes, then noise cancellation effectiveness is improved, but system stability deteriorates due to external changes causing undesirable responses
Solution Approach 1:
The patent implements a feedback mechanism where the error signal from the microphone is continuously monitored and used to control the adaptation process. The system measures the actual noise cancellation performance and adjusts filter coefficients based on this feedback, allowing it to adapt to environmental changes while maintaining stability through controlled updates.
Solution Approach 2:
The patent dynamically changes the adaptation parameter (error threshold) based on system conditions. By comparing the error signal magnitude against a threshold and only updating coefficients when the threshold is exceeded, the system adjusts its sensitivity to environmental changes, improving adaptability while preventing instability from excessive updates.
2Productivity
If adaptive filter coefficients are updated frequently to track environmental changes, then noise cancellation performance is improved, but disruption from de-stabilizing samples increases
Solution Approach 1:
The patent applies partial action by selectively updating filter coefficients only when necessary - specifically when the error signal exceeds a predefined threshold. This prevents excessive updates that would occur with continuous adaptation, reducing disruption from de-stabilizing samples while maintaining adequate responsiveness to genuine environmental changes.
3Speed
If the adaptive filter responds to all error signals, then adaptation speed is improved, but undesirable responses are generated under certain circumstances
Solution Approach 1:
The patent performs preliminary action by establishing a threshold criterion before updating filter coefficients. The error signal is first compared against this threshold, and only updates proceed if the threshold is exceeded. This preliminary check prevents undesirable responses by filtering out spurious error signals before they can destabilize the adaptation process.
Data Source
AI summary
An adaptive noise canceling (ANC) circuit adaptively generates an anti-noise signal from that is injected into the speaker or other transducer output to cause cancellation of ambient audio sounds. At least one microphone provides an error signal indicative of the noise cancellation at the transducer, and the coefficients of the adaptive filter are adapted to minimize the error signal. In order to prevent improper adaptation or instabilities in one or both of the adaptive filters, spikes are detected in the error signal by comparing the error signal to a threshold ambient noise average. Therefore, if the magnitude of the coefficient error is greater than a threshold value for an update, the update is skipped. Alternatively the step size of the updates may be reduced.