Variable Whitening Filter for Hearing Aid Feedback Cancellation
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Solution Overview
Problem
Existing hearing aid systems with feedback cancellation methods suffer from biased acoustic feedback estimation due to autocorrelation in input signals, leading to artefacts when tonal inputs are present, as the whitening filter cannot effectively separate desired tones from feedback-induced oscillations.
Innovation Solution
A listening system with a variable whitening filter that estimates and updates filter coefficients based on an electrical update signal from a secondary input transducer, minimizing acoustic feedback and allowing for accurate reconstruction of the direct input signal, thereby avoiding artefacts and improving feedback cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a whitening filter is used to whiten the microphone signal in feedback cancellation, then the feedback estimation accuracy is improved, but desired tones are removed from the reference and error signals causing feedback cancellation failure
Solution Approach 1:
The patent segments the signal processing into two distinct paths: one for whitening the error signal to improve feedback estimation accuracy, and another for preserving the reference signal without whitening to maintain desired tones. This segmentation allows each path to be optimized independently without interfering with the other's function.
Solution Approach 2:
The patent introduces an intermediary approach by applying the whitening filter only to the error signal rather than to both the reference and error signals as in conventional methods. This selective application acts as an intermediary solution that achieves whitening benefits while preserving the integrity of the reference signal.
2Object-affected harmful factors
If the whitening filter is applied to both reference and error signals, then the input signal is whitened to avoid artefacts, but the reference signal loses desired tone information needed for accurate feedback cancellation
Solution Approach 1:
The patent extracts the whitening operation from the conventional path where it is applied to both signals, and applies it only to the error signal. This extraction preserves the desired tone information in the reference signal while still achieving the whitening effect needed to reduce autocorrelation artefacts in the feedback estimation.
Solution Approach 2:
The patent applies different processing qualities to different signals: the error signal receives full whitening processing to eliminate autocorrelation artefacts, while the reference signal maintains its original spectral characteristics to preserve desired tones. This local differentiation of processing quality resolves the contradiction between artefact removal and information preservation.
Data Source
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AI summary
The invention relates to: A listening system comprising a first input transducer for converting an input sound to an electrical input signal, the electrical input signal comprising a direct part and an acoustic feedback part, an output transducer for converting an electrical output signal to an output sound, a forward path being defined between the input and output transducer and comprising a signal processing unit, a feedback cancellation system for estimating acoustic feedback comprising an adaptive FBC filter arranged in parallel to the forward path, the adaptive FBC filter comprising a variable FBC filter part and an FBC update algorithm part for updating the variable FBC filter part, the FBC update algorithm part comprising first and second FBC algorithm input signals influenced by the electrical input and output signals, respectively, the first and second FBC update algorithm input signal paths comprising first and second variable filters, respectively, the listening system further comprising an electrical update signal essentially consisting of said direct part of said electrical input signal. The invention further relates to a method of improving feedback cancellation and to use of a listening system. The object of the present invention is to provide an alternative scheme for improving acoustic feedback cancellation. The problem is solved in that said first and second variable filters are adapted to be updated on the basis of said electrical update signal. An advantage of the invention is that a desired tone in the input signal is not substantially affected by the feedback cancellation system. The invention may e.g. be used in listening devices comprising active feedback cancellation, e.g. hearing aids, active ear protection devices, etc.