Parallel Feedback Filters for Hearing Devices
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Solution Overview
Problem
Hearing devices face challenges in quickly and effectively reducing feedback artifacts, which can lead to bothersome whistles or echoing sounds due to the time required for adapting feedback filters.
Innovation Solution
A hearing device with a feedback-canceller apparatus that operates multiple filters in parallel, allowing for the selection of the most effective filter based on stored filter coefficients, with adaptive and non-adaptive filters that can be automatically switched to address changing feedback situations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single adaptive filter is used for feedback cancellation, then the filter can be continuously adapted to current feedback situations, but feedback artifacts such as whistles and echoing sounds occur during the adaptation time
Solution Approach 1:
The patent stores multiple sets of filter coefficients in advance, each corresponding to different feedback situations (e.g., different acoustic environments, user positions). When feedback is detected, the system quickly switches between pre-prepared filter sets rather than adapting in real-time, thereby eliminating feedback artifacts during transitions.
Solution Approach 2:
The system changes the parameter of filter coefficients by selecting from multiple pre-stored sets with different characteristics. This allows rapid adaptation to varying feedback conditions without the delay of real-time coefficient adaptation, thus preventing feedback whistles and artifacts.
2Difficulty of detecting and measuring
If the amplification in the hearing aid is set to be sufficiently high to make feedback perceivable, then feedback can be detected for countermeasures, but feedback becomes bothersome to the wearer with shrill-sounding and echoing artifacts
Solution Approach 1:
The patent creates a copy of the feedback signal path by using a separate feedback cancellation pathway that mirrors the main audio signal. This allows the system to detect and cancel feedback without increasing the amplification of the main audio signal, thus making feedback detectable without making it bothersome to the wearer.
3Speed
If feedback is detected and step size is increased for a certain amount of time, then adaptation speed is improved, but feedback whistle or measurable artifact occurs before targeted countermeasure can be taken
Solution Approach 1:
Multiple filter coefficient sets are prepared in advance for different feedback scenarios. When feedback is detected, the system immediately switches to the appropriate pre-prepared filter set rather than increasing step size for gradual adaptation. This eliminates the time delay and prevents feedback whistles from occurring during adaptation.
Solution Approach 2:
The system skips the gradual adaptation process by directly switching between pre-stored filter coefficient sets. This allows the feedback cancellation to take effect immediately without going through intermediate adaptation states that would produce feedback artifacts.
Data Source
AI summary
A hearing device has a signal-processing apparatus for processing an input signal into an output signal, and a feedback-canceller apparatus for reducing feedback artifacts on the basis of the input signal and the output signal. The feedback-canceller apparatus has an adaptive, first filter, for establishing a set of filter coefficients for a predefined feedback situation. The feedback-canceller apparatus is configured to store the set of filter coefficients. It has at least one second filter, which can be operated directly parallel to the first filter on the basis of the stored set of filter coefficients. The adaptive, first filter can be continuously adapted to a current feedback situation, and the feedback-canceller apparatus is configured such that in the current feedback situation it automatically selects either the first or the second filter. As a result, it generally only requires a simple switchover, but not a complete adaptation.