Hearing Aid Active Noise Cancellation Filter Update
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Solution Overview
Problem
Standard adaptive ANC filter updates in hearing aids are challenging due to the desired hearing aid output signal acting as a disturbing signal for the adaptive ANC filter estimation, hindering optimal noise cancellation performance.
Innovation Solution
A modified adaptive ANC filter update system is introduced, featuring a variable feedforward ANC filter with adaptive algorithm coefficients updated based on first and second algorithm input signals, which includes a filtered version of the hearing aid output signal to compensate for the secondary path transfer function, thereby improving noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard adaptive ANC filter update is used in a hearing aid, then the ANC filter can be obtained before use and remain fixed, but the desired hearing aid output signal acts as a disturbing signal for the adaptive ANC filter estimation, degrading noise cancellation performance
Solution Approach 1:
The patent extracts the harmful component (hearing aid output signal) from the error signal by introducing a model of the secondary path. The model generates an estimate of the hearing aid output signal's contribution to the error signal, which is then subtracted to isolate the true noise component for adaptive filter updating.
Solution Approach 2:
The patent introduces a secondary path model as an intermediary element that mediates between the hearing aid output signal and the adaptive filter estimation. This model acts as a bridge to understand and compensate for the distortion introduced by the hearing aid's own output on the error signal.
2Adaptability or versatility
If the adaptive ANC filter uses the hearing aid output signal for update, then the filter can adapt to changes, but the hearing aid output signal interferes with the accurate estimation of the ANC filter coefficients
Solution Approach 1:
The patent extracts the interfering component from the error signal by using the secondary path model to estimate and remove the hearing aid output signal's contribution, leaving only the pure noise component for accurate filter coefficient estimation.
Solution Approach 2:
The patent employs feedback by using the estimated ANC signal (derived from the adaptive filter output and secondary path model) to correct the error signal fed back to the adaptive algorithm, creating a closed-loop system that compensates for self-interference.
3Device complexity
If a fixed ANC filter is used before use, then device complexity is reduced, but optimal noise cancellation performance cannot be achieved as the primary path and secondary path change over time
Solution Approach 1:
The patent enables the ANC system to self-adjust by automatically updating the adaptive filter coefficients based on the corrected error signal. The system serves itself by using its own output and error measurements to continuously optimize its performance without external intervention.
Solution Approach 2:
The patent transitions from a static fixed filter to a dynamic adaptive filter that continuously adjusts its coefficients in response to changing acoustic conditions. The adaptive algorithm enables the filter to track and adapt to temporal variations in the primary and secondary paths.
Data Source
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AI summary
A hearing aid configured to be worn at an ear, at least partially in an ear canal comprising an eardrum, of a user, the hearing aid comprises • a first input transducer (M) for converting first sound in an environment around the hearing aid to a first electric input signal (y) representing said sound in said environment; • a second input transducer (MEC) for converting sound in said ear canal, e.g. at said eardrum, of the user to a second electric input signal (e) representing said sound in said ear canal, e.g. at said eardrum; • a hearing aid processor (G) for processing said first and second electric input signals, or signals depending thereon, and to provide a processed signal (yG) based thereon; • an output transducer (SPK) for converting said processed signal, or a signal depending thereon, (u), to acoustic stimuli presented to said eardrum of the user; • an active noise cancellation system (ANCS) configured to cancel or reduce directly propagated sound (xp) from said environment to said eardrum of the user, said active noise cancellation system comprising an adaptive filter (C, EST) configured to provide a feedforward cancellation signal (yc) to compensate the directly propagated sound (xp) of an acoustic propagation path (P) from said first input transducer to said second input transducer, and a combination unit (+) for combining, e.g. subtracting, said estimate (yc) of the directly propagated sound (xp) with, e.g. from, said processed signal (yG), the adaptive filter comprising a variable filter (C) and an adaptive algorithm (EST), the adaptive algorithm (EST) being configured to provide update filter coefficients (cUPD) to the variable filter (C) in dependence of first and second algorithm input signals. The first algorithm input signal (ys) comprises said first electric input signal (y), or a signal dependent thereon, and said second algorithm input signal (ec) comprises a combination of said second electric input signal (e) and said processed signal (yG), or a signal or signals depending thereon. A method of operating a hearing aid is further disclosed. The invention may e.g. be used in hearing aids or headsets.