Hearing Aid Feedback Control Using Correlation Detection
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Solution Overview
Problem
Existing hearing aid feedback control systems struggle to effectively distinguish between feedback-related artefacts and tonal signals in acoustic environments, leading to performance degradation and increased audibility of artefacts, especially in scenarios with strong autocorrelation or external tones.
Innovation Solution
A hearing aid system with a feedback control mechanism that utilizes a correlation detection unit to differentiate between feedback-induced tonal sounds and external tonal sounds by calculating a correlation measure and its processed version, adjusting the adaptive filter's adaptation rate based on these measures, and enabling or disabling frequency shifting to minimize artefacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive feedback cancellation is used to track feedback path changes, then feedback control performance is improved, but the system introduces artefacts when strong autocorrelation (tones) are present in the input signal
Solution Approach 1:
The patent applies dynamics by making the adaptation rate of the adaptive filter variable rather than fixed. The adaptation rate is dynamically adjusted based on the detected correlation measure between input and output signals. When high correlation is detected (indicating tonal components), the adaptation rate is reduced to prevent artefact generation. When low correlation is detected, the adaptation rate is increased to improve feedback tracking performance.
Solution Approach 2:
The patent changes the parameter of adaptation rate based on the correlation measure. By monitoring the correlation between input and output signals and adjusting the adaptation rate accordingly, the system optimizes feedback cancellation while avoiding artefact introduction in tonal environments.
2Measurement precision
If the adaptation rate is increased to improve feedback tracking, then feedback control accuracy is improved, but the system becomes more sensitive to tonal signals causing wrong feedback detection
Solution Approach 1:
The patent uses feedback by continuously monitoring the correlation measure between input and output signals and using this information to adjust the adaptation rate. This closed-loop control ensures that the system adapts its behavior based on the actual signal conditions, improving both accuracy and reliability.
Solution Approach 2:
The adaptation rate is made dynamic and responsive to signal conditions. Rather than using a fixed high adaptation rate that causes false feedback detection in tonal environments, the system dynamically adjusts the rate based on real-time correlation analysis, maintaining reliability across different acoustic conditions.
3Measurement precision
If frequency shift is applied to de-correlate input and output signals, then feedback estimation quality is improved, but audibility of artefacts increases in tonal environments
Solution Approach 1:
The frequency shift amount is made dynamic rather than fixed. The system adjusts the frequency shift based on the detected correlation measure and presence of tonal components. When tonal signals are detected, the frequency shift is reduced or disabled to minimize artefact audibility, while maintaining sufficient de-correlation for accurate feedback estimation in non-tonal environments.
Data Source
AI summary
A hearing aid is configured to be worn in and/or at an ear of a user, and comprises a) an input transducer for converting an input sound to an electric input signal representing sound, h) an output transducer for converting a processed electric output signal to an output sound, c) a signal processor operationally coupled to the input and output transducers and configured to apply a forward gain to the electric input signal or a signal originating therefrom, wherein the input transducer, the signal processor and the output transducer forming part of a forward path of the hearing aid. The hearing aid further comprises d) a feedback control system for compensating for acoustic or mechanical feedback of an external feedback path from the output transducer to the input transducer, wherein the feedback control system comprises i) a feedback estimation unit for providing a feedback estimate signal of said external feedback path, ii) a combination unit located in the forward path for combining the electric input signal or a signal derived therefrom and the feedback signal detected by said estimation unit, to provide a resulting feedback corrected signal, iii) a correlation detection unit configured to determine a correlation measure between said feedback corrected signal and said output signal, said correlation detection unit further configured to provide a processed version of said correlation measure.