Hearing Aid Beamformer Gain Control for Feedback Stability
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Solution Overview
Problem
State-of-the-art hearing aids face mechanical instability due to excessive loop gain when beam-forming is used, leading to feedback artifacts, as the amplification limits set by Full-On Gain (FOG) do not account for beam-forming contributions, which can result in inadequate amplification for users' hearing impairments.
Innovation Solution
A hearing aid system dynamically adjusts the amplification gain and beamformer gain to ensure the electrical gain does not exceed the Full-On Gain (FOG) value, prioritizing amplification gain to compensate for user hearing impairments, while allowing some gain for beamforming, by using a gain control unit that modifies the Full-On Gain (FOG) based on directional gains and previously determined values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If beam-forming is used to attenuate noise from directions other than the desired listening direction, then noise reduction is improved, but the loop gain increases causing mechanical instability and feedback artifacts
Solution Approach 1:
The system dynamically adjusts the beam-forming weights and gain distribution based on real-time acoustic conditions. The directional gains applied to individual microphone signals are continuously optimized to maintain noise reduction while keeping the electrical gain within stable limits, preventing mechanical feedback instability.
Solution Approach 2:
The patent modifies the electrical gain parameters by dynamically adjusting the beam-forming weights and applying frequency-dependent gain compensation. This allows the system to change the distribution of gain between the beam-forming stage and the amplification stage, thereby controlling the loop gain to remain below instability thresholds while maintaining effective noise reduction.
2Reliability
If the Full-On Gain limit is strictly enforced to maintain stability, then mechanical feedback is prevented, but insufficient amplification is provided for users with hearing impairments
Solution Approach 1:
The system implements dynamic gain management where the amplification level is continuously adjusted based on the current beam-forming configuration and acoustic conditions. This allows the hearing aid to provide maximum effective amplification within the stability constraints, adapting in real-time to maintain both stability and hearing assistance effectiveness.
Solution Approach 2:
The system uses feedback mechanisms to monitor the loop gain and acoustic feedback conditions, continuously optimizing the gain distribution between beam-forming and amplification stages. This ensures that the Full-On Gain limit is respected for stability while maximizing the useful amplification for the user's hearing needs.
3Object-affected harmful factors
If beam-forming weights are increased to improve spatial filtering, then directional noise attenuation is enhanced, but the individual microphone gains become excessively large contributing to loop gain instability
Solution Approach 1:
The patent applies frequency-dependent gain compensation and dynamic weight optimization to adjust the beam-forming parameters. By modifying the weights and gain distribution as a function of frequency and acoustic conditions, the system achieves effective spatial filtering without allowing individual microphone gains to become excessively large, thereby maintaining loop gain stability.
4Productivity
If the hearing aid provides maximum amplification to compensate for hearing impairments, then user hearing needs are met, but the device exceeds the Full-On Gain limit causing mechanical feedback
Solution Approach 1:
The system dynamically manages the gain distribution between beam-forming and amplification stages based on real-time conditions. This allows the hearing aid to provide maximum effective amplification for the user's hearing impairment while continuously adapting to stay within the Full-On Gain stability limit, preventing mechanical feedback.
Data Source
AI summary
The application relates to a hearing aid comprising a forward path comprising a) a multitude of input units for providing a multitude of electric input signals INi, i=1, . . . , M, representative of sound, b) a multi input beam former filtering unit for providing a beam formed signal YBF from said multitude of electric input signals, c) a gain unit for applying a hearing aid gain GHA to said beam formed signal YBF, and providing a processed signal, and d) an output unit for providing stimuli perceivable by a user as sound based on said processed signal or a signal derived therefrom. The hearing aid further comprises e) a gain control unit for limiting said hearing aid gain GHA to a modified full-on gain value G′FOG. The multi input beam former filtering unit is configured to apply a current frequency dependent directional gain GDIR,i to each of said multitude of electric input signals INi, and the gain control unit is configured to determine the modified full-on gain value G′FOG in dependence of said current directional gains GDIR,i, i=1, . . . , M, and a previously determined full-on gain value GFOG. Thereby an improved hearing aid is provided. The invention may e.g. be used for hearing instruments, headsets, or active ear protection systems.