Hearing Device Microphone Array Feedback Suppression
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Solution Overview
Problem
Hearing devices often experience feedback loops that lead to whistling due to uncontrolled directional characteristics of microphone arrays, particularly when amplifying signals for hearing loss compensation, which can result in unstable systems and bothersome noise.
Innovation Solution
A method for operating a hearing device with a microphone array where a directional parameter is set to satisfy stability conditions, restricting possible values to prevent feedback, using an overall transfer function that includes directional and feedback path transfer functions to ensure a gain less than one, and employing an adaptation algorithm to control feedback suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the directional characteristic of the microphone array is made adjustable to optimize hearing in different directions, then the adaptability is improved, but the risk of feedback and system instability increases
Solution Approach 1:
The patent implements dynamic adjustment of the directional parameter within predefined stable ranges. The control unit continuously monitors system stability and adjusts the directional characteristic of the microphone array in real-time based on current operating conditions, allowing the system to adapt to different listening situations while maintaining feedback-free operation through constrained parameter values.
2Power
If the gain is increased to compensate for hearing loss, then the hearing support is improved, but the feedback effect is amplified leading to whistling
Solution Approach 1:
The patent changes the directional parameter of the microphone array to values that have been predetermined to prevent feedback. By adjusting the directional characteristic (e.g., beamforming angles, null positions) rather than simply reducing gain, the system maintains high amplification for hearing support while redirecting the microphone sensitivity pattern to avoid picking up feedback paths from the ear canal vent or bone conduction routes.
3Measurement precision
If the directional parameter is freely adjustable to maximize signal capture, then the signal-to-noise ratio is improved, but feedback suppression becomes difficult
Solution Approach 1:
The patent performs preliminary determination of stable directional parameter ranges before actual operation. During a setup or calibration phase, the system identifies which directional parameter values maintain feedback-free operation for the specific user's anatomy and listening environment. These predetermined stable ranges are then used to constrain the directional parameter during normal operation, ensuring both good signal capture and feedback suppression.
Data Source
AI summary
Sound from the receiver of a hearing device may be fed back to its microphones via acoustic feedback paths, which may cause undesirable whistling. It is particularly difficult to predict the creation of feedback in a microphone array with adjustable directional characteristic. This is because the stability of the system then is dependent on a directional parameter by way of which the directional characteristic is fixed. The invention enables feedback-free operation of such a hearing device. A prescribed stability condition is used to establish for which values of the directional parameter feedback-free operation is possible. The directional parameter is then restricted to these values during operation of the hearing device. As an alternative thereto, a value for a strength of a feedback effect is established for a current value of the directional parameter and the directional parameter or a control parameter for the purpose of feedback suppression is then set as a function of the established value.