Auto Regressive Filter for Hearing Aid Feedback Control
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Solution Overview
Problem
Digital hearing aids with adaptive feedback cancellers face artifacts due to periodic input signals, which cause entrainment artifacts like whistle-like sounds, reducing output signal quality.
Innovation Solution
An auto regressive unit is used to measure the acoustic feedback path, providing a ratio of predictive estimates to adjust the adaptation rate of the adaptive feedback cancellation filter, preventing entrainment artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an adaptive feedback canceller is used to model external acoustic feedback, then feedback cancellation performance is improved, but entrainment artifacts occur when the input signal is periodic
Solution Approach 1:
A correlation detection unit is introduced as an intermediary component between the microphone signal and the adaptive feedback canceller. This unit detects the correlation between the microphone signal and delayed receiver signal, and provides control signals to adjust the adaptation rate of the feedback canceller, thereby preventing entrainment artifacts while maintaining feedback cancellation performance
Solution Approach 2:
The adaptation rate of the feedback canceller is made dynamic rather than fixed. The correlation detection unit continuously monitors signal correlation and adjusts the adaptation rate accordingly - reducing it when periodic signals are detected to prevent entrainment, and maintaining it at normal levels when no periodic signals are present to ensure effective feedback cancellation
2Measurement precision
If the adaptive feedback canceller continuously adapts to trace correlation, then feedback cancellation accuracy is improved, but periodic signals cause undesired correlation that degrades performance
Solution Approach 1:
A feedback control mechanism is implemented where the correlation detection unit monitors the relationship between microphone and receiver signals, and feeds back control information to the adaptive feedback canceller. This feedback loop enables the system to distinguish between desired correlation (acoustic feedback) and undesired correlation (periodic input signals), adjusting adaptation accordingly to maintain both accuracy and reliability
Data Source
AI summary
A method of signal processing an input signal in a hearing aid to avoid entrainment, the hearing aid including a receiver and a microphone, the method comprising using an adaptive filter to measure an acoustic feedback path from the receiver to the microphone and adjusting an adaptation rate of the adaptive filter using an output from a filter having an autoregressive portion, the output derived at least in part from a ratio of a predictive estimate of the input signal to a difference of the predictive estimate and the input signal.