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Detection of feedback path change

a feedback path and detection technology, applied in the field of detection of feedback path change, can solve the problems of significant contamination of desired audio input signal, biased estimation of acoustic feedback path (provided by adaptive filter), and audible feedback

Active Publication Date: 2022-10-27
EARGO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The patent text describes a method that can reduce squeal when changing the feedback path in an audio device. The method involves reducing the gain applied to at least one of the audio signals or the subband audio signals. This can make the audio device more stable and less sticky.

Problems solved by technology

As this cycle continues, the effect of acoustic feedback becomes audible as artefacts, squealing, etc. when the system becomes unstable.
The problem appears typically when the microphone and the loudspeaker are placed closely together, as e.g. in hearing aids or other audio systems.
Unstable systems due to acoustic feedback tend to significantly contaminate the desired audio input signal with narrow band frequency components, which are often perceived as squeal or whistle.
The filter update may be calculated using stochastic gradient algorithms, including some form of the Least Mean Square (LMS) or the Normalized LMS (NLMS) algorithms A drawback of these methods is that the estimate of the acoustic feedback path (provided by the adaptive filter) will be biased, if the input signal to the system is not white (i.e. if there is autocorrelation) because the estimate is made in a ‘closed loop’.
Feedback in acoustic systems, especially hearing aids, is prevalent because of air conduction paths that exist between the output of the system and its input.
Other physical paths can also cause feedback; for example a loose package may be subject to transmitting vibrations from output back to the input.
A negative side-effect of some adaptive FBC algorithms is the occurrence of entrainment artifacts.

Method used

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Examples

Experimental program
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example 1

[0125]FIG. 3 plots the magnitude of the BEAll metric against time, in seconds. BeAll(n) is labeled as reference numeral 302. In this example, the value of BEAll never equaled or exceed the value of BEThresh (BEThresh was set to a log2 value of +16.0 in this example, as well as in the examples referencing FIGS. 4-8) and therefore feedback path change was not detected and μ(n) was maintained at the slow rate over the entire 5 second duration of this example. The value of 13 used for calculating BESmooth was 2−3, and the value of y used for calculating BESlow was 2−13 for this example and the examples referencing FIGS. 4-8. Example 1 shown in FIG. 3 used music as input. The music inputted was a new age piano solo title “Joy”, by George Winston, which includes multiple segments of single notes, i.e., pure tones. The maximum value of the signal was down −23 dB from full scale. FIG. 3 shows that the metric 302 stays well below the threshold value of +16.0 throughout the duration of the ex...

example 2

[0126]FIG. 4 shows the BEAll metric 302 in a simulation where the signal analyzed is human speech. After the start-up period (e.g. from zero up to about 1.5 seconds) has passed to allow for settling of the metrics, it can be observed in FIG. 4 that the value of BEAll metric 302 never equals or exceeds the BEThresh value of +16.0, therefore feedback path change is not detected and the slow rate for μ(n) was maintained throughout the duration of this experiment. Thus, the metric 302 is able to distinguish the tonal parts of human speech from feedback and the tonal parts of the speech do not cause the metric 302 to equal or exceed the threshold value.

example 3

[0127]FIG. 5 shows the BEAll metric 302 in a simulation where the signals analyzed are the sounds made by “clicking” a retractable ball point pen when the pen is actuated to repeatedly extend and retract the ball point of the pen. The impulsive sounds produced by the pen clicks are shown by the downward spikes 312 in the plot. The downward spikes 312 resulting from the clicks are correctly interpreted and are not identified as feedback path change, as only positive values greater than or equal to the threshold value (+16.0 in this example) are recognized as feedback path change. Therefore the slow rate for μ(n) was maintained throughout the duration of this experiment, since the metric 302 never equals or exceed the threshold value.

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Abstract

Methods and systems for signal processing an audio signal in a hearing device to detect when feedback path change occurs and controlling an adaptive feedback canceler to remove the feedback are provided. The hearing device includes a receiver and a microphone. An exemplary method includes detecting whether a tonal signal is caused by a feedback path change by estimating a product of a subband error signal and a subband output signal generated in response to a subband audio input signal; estimating a fast metric based on the estimated product and estimating a slow metric; and applying or maintaining an adaptation rate to the adaptive feedback canceler of the hearing device, wherein the adaptation rate applied or maintained is selected based upon a value of the difference between the fast and slow metrics compared to a threshold value.

Description

FIELD OF THE INVENTION[0001]This disclosure relates to detection of the onset of feedback in feedback cancellation subsystems of acoustic systems, and more particularly to such for feedback cancellation subsystems in hearing devices.BACKGROUND OF THE INVENTION[0002]Acoustic feedback occurs because the output speaker signal from an audio system providing amplification of a signal picked up by a microphone is partly returned to the microphone via an acoustic coupling through the air or other media. The part of the output signal returned to the microphone is then re-amplified by the system before it is re-presented at the speaker, and again returned to the microphone. As this cycle continues, the effect of acoustic feedback becomes audible as artefacts, squealing, etc. when the system becomes unstable. The problem appears typically when the microphone and the loudspeaker are placed closely together, as e.g. in hearing aids or other audio systems. Some other classic situations with feed...

Claims

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Application Information

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IPC IPC(8): H04R25/00
CPCH04R25/453H04R25/43H04R25/505H04R2225/023H04R1/1016H04R3/02H04R2430/03
Inventor SORENSEN, BRYANT E.STEELE, BRENTON
Owner EARGO
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