Hearing Device Feedback Cancellation Bias Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Acoustic feedback in hearing devices and audio systems causes performance degradation and instability, leading to issues like howling, due to the correlation between input and output signals introduced by frequency shifting, which results in biased adaptive filter estimation.
Innovation Solution
A correction unit is implemented to subtract the residual bias introduced by frequency shifting from the feedback path estimate, using a second adaptive filter and frequency analysis to determine dominant frequencies and correct the feedback signal, thereby reducing the periodic bias in the adaptive filter estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency shifting is applied to de-correlate input and output signals, then feedback cancellation performance is improved, but residual bias is introduced in the adaptive filter estimation
Solution Approach 1:
The patent extracts and removes the residual bias component from the adaptive filter estimation. The correction unit specifically targets and subtracts the bias introduced by frequency shifting, separating the useful de-correlation effect from the harmful estimation bias to achieve both improved feedback cancellation and accurate adaptation
Solution Approach 2:
The patent modifies the estimation process by changing the parameter being estimated - instead of directly estimating the feedback path, the system estimates the bias component introduced by frequency shifting and subtracts it. This parameter transformation allows the system to maintain the benefits of frequency shifting while correcting the resulting estimation error
2Measurement precision
If adaptive filter estimation is performed without frequency shifting, then unbiased estimation is achieved, but correlation between input and output signals persists causing feedback instability
Solution Approach 1:
The patent introduces frequency shifting as an intermediary mechanism that breaks the direct correlation between input and output signals. This intermediary transformation allows the adaptive filter to converge by reducing signal correlation, while the correction unit acts as a second intermediary to remove the bias introduced by this necessary transformation
3Reliability
If frequency shifting is used to reduce feedback correlation, then feedback cancellation is improved, but periodic time-varying bias is introduced in the estimate
Solution Approach 1:
The patent converts the harmful periodic bias introduced by frequency shifting into a detectable and correctable artifact. By analyzing the characteristics of the bias and using the correction unit to subtract it, the system transforms what was previously a detrimental side effect into an opportunity for improved estimation accuracy through explicit bias compensation
Data Source
Figure 1~2
Figure 3
Figure 4~6
AI summary
The application relates to a hearing device, e.g. a hearing aid, comprising a) an input transducer for converting an input sound to an electric input signal representing sound, b) an output transducer for converting a processed electric output signal to an output sound, c) a signal processing unit operationally coupled to the input and output transducers and configured to apply a forward gain to the electric input signal or a signal originating therefrom, and d) a frequency shifting unit for de-correlating the processed electric output signal and the electric input signal. The input transducer, the signal processing unit, the frequency shifting unit, and the output transducer form part of a forward path of the hearing device. The hearing device further comprises e) a feedback cancellation system for reducing a risk of howl due to acoustic or mechanical feedback of an external feedback path from the output transducer to the input transducer. The feedback cancellation system comprises e1) a feedback estimation unit comprising e1.1) a first adaptive filter for providing an estimate of said external feedback path, and e2) a combination unit located in the forward path. The feedback estimation unit provides a resulting feedback estimate signal, which is combined with the electric input signal or a signal derived therefrom in the combination unit to provide a resulting feedback corrected signal. The application further relates to a method of operating a hearing device. The object of the present application is to improve feedback cancellation in hearing devices. The problem is solved in that the feedback estimation unit further comprises e1.2) a correction unit for influencing said estimate of the feedback path by diminishing a residual bias in said resulting estimate of the feedback path, said residual bias being (e.g. a result of the frequency shift) introduced by the frequency shifting unit. This has the advantage of improving feedback cancellation, in particular in an acoustic environment comprising tonal components. The invention may e.g. be used for the hearing aids, headsets, ear phones, active ear protection systems, handsfree telephone systems, mobile telephones, teleconferencing systems, public address systems, karaoke systems, classroom amplification systems, etc.