Hearing Aid Feedback Filter Control for Tonal Signal Discrimination
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Solution Overview
Problem
Existing hearing apparatuses face challenges in effectively controlling the adaptation speed of adaptive filters to reduce feedback whistling, leading to either slow adaptation or misadaptation, especially with tonal input signals, which affects sound quality.
Innovation Solution
A method that involves picking up sound signals, generating earpiece signals, reducing feedback signals using an adaptive filter, and controlling the adaptation increment based on autocorrelation values obtained from shifted frequency signals, allowing for rapid adaptation while minimizing artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the adaptation increment of the adaptive filter is increased to achieve rapid feedback compensation, then the feedback suppression speed is improved, but misadaptation occurs with tonal input signals leading to degraded sound quality
Solution Approach 1:
The adaptation increment is made dynamic rather than fixed. The system automatically adjusts the adaptation increment based on the detected signal characteristics - using high adaptation increments for rapid feedback suppression when needed, and low adaptation increments for stable sound quality during tonal signals. This dynamic adjustment resolves the contradiction between speed and reliability.
Solution Approach 2:
The system changes the adaptation increment parameter based on autocorrelation analysis of the input signal. By monitoring signal characteristics and adjusting the adaptation increment parameter accordingly, the system achieves both rapid adaptation when necessary and maintains sound quality during tonal periods, thus resolving the contradiction.
2Reliability
If the adaptation increment is decreased to prevent misadaptation with tonal signals, then sound quality is maintained, but feedback compensation becomes slow
Solution Approach 1:
The system dynamically adjusts the adaptation increment based on real-time signal analysis. When feedback conditions are detected, the adaptation increment is increased for rapid suppression. When tonal signals are present, it is decreased to maintain sound quality. This dynamic behavior resolves the contradiction between maintaining sound quality and achieving fast feedback suppression.
Solution Approach 2:
The system periodically analyzes the autocorrelation of the input signal to determine the appropriate adaptation increment. This periodic monitoring allows the system to switch between different adaptation rates based on signal characteristics, ensuring both sound quality maintenance and rapid feedback suppression when needed.
3Device complexity
If a fixed adaptation increment is used, then the device complexity is reduced, but the system cannot distinguish between feedback whistling and tonal signals leading to either slow adaptation or misadaptation
Solution Approach 1:
The system uses the autocorrelation function, which is already computed for other signal processing purposes, to detect tonal signals and adjust the adaptation increment. This self-service approach allows the system to gain signal discrimination capability without adding significant complexity, as it leverages existing computational resources.
Solution Approach 2:
The autocorrelation computation serves multiple functions: it is used for both signal analysis and adaptation increment control. This multi-functionality allows the system to distinguish between feedback and tonal signals while maintaining relatively simple device architecture, resolving the contradiction between complexity and adaptability.
Data Source
AI summary
Feedback whistling and external tonal signals are distinguished during feedback suppression. For that purpose an adaptation increment of an adaptive filter of a hearing apparatus for feedback reduction is controlled. A sound signal is picked up by a microphone and a microphone signal is output, from which an earpiece signal for an earpiece is generated. An adaptive filter reduces a feedback signal in the microphone signal. To this end an autocorrelation value of sampled values of the microphone signal, between which a time difference exists, is obtained, and the adaptation increment of the adaptive filter is controlled based on the autocorrelation value. A frequency of an output signal obtained on the basis of the microphone signal is shifted while creating the earpiece signal and the time difference for obtaining the autocorrelation value is controlled as a function of the shifting of the frequency of the microphone signal.