US-12621613-B2 - Method of detecting a sudden change in a feedback/echo path of a hearing aid

US12621613B2US 12621613 B2US12621613 B2US 12621613B2US-12621613-B2

Abstract

A method of detecting a sudden change in a feedback/echo path of a hearing aid is based on a gradient of an adaptive filter comprising an adaptive algorithm configured to estimate the feedback/echo path. The method may comprise comparing a smoothed and processed version of the gradient values over time to a threshold value. A hearing aid configured to detect a sudden change in a feedback/echo path is furthermore provided.

Inventors

Bernhard KUENZLE
Martin KURIGER
Meng Guo

Assignees

OTICON A/S

Dates

Publication Date: 20260505
Application Date: 20230419
Priority Date: 20201228

Claims (15)

1 . A method of detecting a sudden change in a feedback/echo path of a hearing aid comprising: S1. estimating a feedback path using an adaptive algorithm employed by an adaptive filter to detect the sudden change in the feedback/echo path; S2. smoothing a gradient of the adaptive algorithm over time; S3. performing an operation on the smoothed gradient to provide a modified gradient; S4. determining whether the gradient or the modified gradient fulfils an instability criterion; and S5. detecting the sudden change in the feedback/echo path as a result of the instability criterion being fulfilled.
2 . A method according to claim 1 , further comprising: comparing a smoothed and processed version of gradient values of the adaptive algorithm over time to a threshold value.
3 . A method according to claim 1 , further comprising in response to the instability criterion being fulfilled, updating the adaptive feedback path estimate of the adaptive algorithm and/or adapting another processing of the hearing aid when.
4 . A method according to claim 3 , wherein said another processing of the hearing aid comprises detecting directionality.
5 . A method according to claim 1 , wherein the instability criterion is fulfilled when the one or more gradient values, or modified gradient values, or a weighted combination of said one or more gradient values, or modified gradient values, are larger than a threshold value.
6 . A method according to claim 1 , further comprising: repeating steps S1-S4 when the instability criterion is not fulfilled.
7 . A method according to claim 1 , further comprising determining a feedback path change from the gradient, or the smoothed or modified gradient, when the instability criterion is fulfilled.
8 . A method according to claim 1 , wherein step S2 comprises smoothing a gradient vector g (n) of adaptive filter coefficients over time, where n is a time index, by using a first-order filter with a coefficient a, wherein the smoothing of the gradient vector g(n) is performed according to the following formula: g sm ( n )= a*g ( n )+(1− a )* g sm ( n− 1), where a is a small and positive number, and where the elements of the gradient vector g (n) are constituted by the gradients to adapt the respective filter coefficients of the adaptive filter from one time step to the next.
9 . A method according to claim 8 wherein step S3 comprises performing operations (O) on the vector entries of the smoothed gradient vector g sm (n) to obtain an operations vector g O (n) as follows: g O ( n )= O ( g sm ( n )), wherein the operations (O) comprise one or more of min, max, median, sum, mean, and abs.
10 . A method according to claim 9 , wherein step S4 comprises performing a comparison of the operations vector g O (n) with a feedback criterion comprising a threshold value (THV) to determine a feedback/echo path change, g O ( n )>THV? wherein the threshold value may be a single value, or a threshold vector.
11 . A method according to claim 10 , wherein the feedback/echo path change is determined as g O (n)>THV in step S4.
12 . A method according to claim 1 , further comprising taking a first action when the feedback criterion is fulfilled, and taking a second action or no action when the feedback criterion is not fulfilled.
13 . A method according to claim 12 , wherein a first action comprises initiating a change of the feedback/echo path estimate, or changing an adaptation rate of the adaptive algorithm, or changing a mode of operation of the hearing aid.
14 . A method according to claim 1 , further comprising determining current gradient values of the adaptive algorithm to adapt one or more of current filter coefficients of the adaptive filter and to provide smoothed and possibly further processed, versions thereof.
15 . A hearing aid comprising: an adaptive filter employing an adaptive algorithm to detect the sudden change in the feedback/echo path; and a controller configured to detect a sudden change in a feedback/echo path of the hearing aid by executing a process including S1. estimating a feedback path using an adaptive algorithm employed by an adaptive filter to detect a sudden change in the feedback/echo path; S2. smoothing a gradient of the adaptive algorithm over time; S3. performing an operation on the smoothed gradient to provide a modified gradient; S4. determining whether the gradient or the modified gradient fulfils an instability criterion; and S5. detecting the sudden change in the feedback/echo path as a result of the instability criterion being fulfilled.

Description

This application is a Divisional of copending application Ser. No. 17/560,611, filed on Dec. 23, 2021, which claims priority under 35 U.S.C. § 119(a) to Application No. 20217344.9, filed in Europe on Dec. 28, 2020, and Application No. 21157068.4, filed in Europe on Feb. 15, 2021, all of which are hereby expressly incorporated by reference into the present application. BACKGROUND The background of the present disclosure is in the technical area of adaptive filter control, more specifically in feedback and/or echo path change and detection, e.g. in hearing aids or headsets. Traditional adaptive filters used for feedback cancellation have a trade-off between convergence/tracking and steady-state errors. It means that many times the convergence/tracking of the adaptive filters needs to be compromised to obtain reasonable steady-state errors. This limits how fast an adaptive filter can cancel feedback upon a change of feedback situation, e.g., when the user wearing a hearing aid gets too close to a hard surface. SUMMARY The present disclosure proposes a method/procedure to speed up the adaptive filter convergence/tracking upon critical changes of feedback situations, without sacrificing goal of obtaining reasonable steady-state errors. The present disclosure further describes a simple method to rapidly detect a feedback/echo path change, which would require a reaction from a feedback/echo cancellation systems, e.g. in that the adaptive filters in these systems need to adapt to the new feedback/echo paths upon the changes. These rapid detections can be used to change programs, e.g. different applications of gain/directionality, etc., in an audio system. A Hearing Aid: In a general aspect, a hearing aid with an improved feedback control system is provided (see e.g. FIG. 1A). The hearing aid comprises a forward path for processing an audio signal. The forward path may e.g. comprise A) an input transducer configured to convert sound in an environment of the user to an electric input signal representing the sound, B) a processor for processing said electric input signal, or a signal derived therefrom (e.g. a feedback corrected signal), and for providing a processed signal, and C) an output transducer for converting the processed signal, or a signal derived therefrom, to stimuli perceivable by the user as sound. The forward path may e.g. provide a forward path transfer function (F, e.g. F(k,n), where k and n are frequency and time indices, respectively). The forward path transfer function (F) may e.g. be configured to compensate for a hearing impairment of a user of the hearing aid. The hearing aid may e.g. further comprise D) a feedback control system for handling external feedback from the output transducer to the input transducer. The feedback control system may e.g. comprise E) an adaptive filter comprising an adaptive algorithm. The adaptive filter may e.g. be configured to provide a current estimate of a feedback signal from the output transducer to the input transducer. The feedback control system may e.g. further comprise F) a combination unit configured to subtract the current estimate of the feedback signal from the electric input signal, or a processed version thereof, and to provide a feedback corrected signal, termed the error signal. The processor may e.g. be configured to base its processing on the error signal. The feedback control system may e.g. further comprise G) a feedback change estimator configured to provide an (instant or fast) estimate of a feedback path transfer function (or a sudden change thereof) in dependence of the forward path transfer function, and optionally a current estimate of the feedback path transfer function provided by the adaptive algorithm. The feedback control system may e.g. further comprise H) an adaptive filter controller for providing an update transfer function estimate for the adaptive filter in dependence of the (instant or fast) estimate of the feedback path transfer function. The (instant or fast) estimate of the feedback path transfer function is e.g. intended to be provided from one time index (n) to the next (n+1) (as opposed to the current estimate of the feedback path transfer function provided by the (adaptive algorithm of the) adaptive filter. The feedback control system may comprise a feedback instability detector for monitoring the fulfillment of a feedback path instability criterion (e.g. indicating a sudden change or instability of the feedback path transfer function). In case the feedback path instability criterion is fulfilled, the (instant or fast) estimate of the feedback path transfer function is intended to override the current estimate of the feedback path transfer function provided by the adaptive filter (the adaptive algorithm) to thereby provide a faster convergence of the adaptive algorithm. It is the intention that the adaptive algorithm continues its feedback path estimation using the (instant or fast) estimate of the feedback path transfer