Hearing Aid Adaptive Feedback Suppression
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Solution Overview
Problem
Hearing aids face challenges with acoustic feedback, particularly in Complete In the Canal (CIC) models, where feedback becomes audible due to low attenuation and short delays, and existing adaptive filters struggle to balance convergence rate and signal distortion, especially when dealing with speech and music signals.
Innovation Solution
A hearing aid system with a pair of equalization filters that selectively frequency equalize and decorrelate only the relevant frequency bands for feedback cancellation, using adaptive and non-adaptive filters to achieve faster and more uniform adaptation, while ignoring irrelevant frequency ranges to minimize distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the convergence rate of the adaptive filter is increased to cope with sudden changes in the acoustic environment, then the feedback cancellation performance is improved, but signals representing speech or music become distorted due to excessive correlation removal
Solution Approach 1:
The patent implements dynamic control of the adaptive filter by introducing a variable step size that adapts based on signal characteristics. The step size is reduced when speech or music signals are detected (high correlation) and increased when feedback cancellation is prioritized (low correlation), allowing the system to dynamically balance between preventing distortion and maintaining feedback cancellation effectiveness
Solution Approach 2:
The patent changes the convergence parameter (step size) of the adaptive filter based on the detected signal type and correlation level. By monitoring the correlation of the input signal and adjusting the step size accordingly, the system optimizes the trade-off between feedback cancellation performance and signal integrity preservation
2Productivity
If a larger than optimal size vent is used to improve sound transmission, then the hearing aid performance is enhanced, but acoustic feedback becomes audible in the form of whistling or howling noise
Solution Approach 1:
The patent implements an active feedback cancellation system that uses a feedback path model to generate an anti-phase signal. This cancellation signal is subtracted from the output signal to eliminate audible feedback caused by large vent sizes, allowing the hearing aid to maintain both high performance and comfort without whistling or howling noises
3Speed
If the adaptive filter operates quickly to remove correlation from the input signal, then the feedback cancellation responds faster to environmental changes, but signals representing speech or music are distorted
Solution Approach 1:
The patent dynamically adjusts the adaptation speed of the filter by implementing a variable step size that responds to the correlation characteristics of the input signal. When speech or music is detected (high correlation), the step size is reduced to prevent distortion. When the signal has low correlation (non-speech), the step size increases to maintain fast adaptation for feedback cancellation
Solution Approach 2:
The convergence parameter (step size) is changed based on the detected signal type and correlation level, optimizing the trade-off between adaptation speed and signal integrity
Data Source
AI summary
A hearing aid comprises an input transducer (2), a subtraction node for subtracting a feedback cancellation signal from the electrical input signal thereby generating a processor input signal, a signal processor (3), an output transducer (4), a pair of equalization filters (7a, 7b) for selecting from the processor input and output signals a plurality of frequency band signals, a frequency equalization unit for frequency equalization for the selected frequency band signals, and an adaptive feedback estimation filter (5, 6) for adaptively deriving the feedback cancellation signal from the equalized frequency band signals. The equalization of selected frequency bands of the input signals of the adaptive feedback cancellation filter provides for an improved and in particular a faster adaption of the feedback cancellation. The invention further provides a method of reducing acoustic feedback of a hearing aid, and a hearing aid circuit.