Adaptive feedback cancellation in hearing aids with clipping in the feedback path

Abstract

Adaptive linear filtering algorithms are commonly used to cancel feedback in hearing aids. The use of these algorithms is based on the assumption that the feedback path is linear, so nonlinearities in the feedback path may affect performance. This study investigated the effect on feedback canceller performance of clipping of the feedback signal arriving at the microphone, as well as the benefit of applying identical clipping to the cancellation signal so that the cancellation path modeled the nonlinearity of the feedback path. Feedback signal clipping limited the amount of added stable gain that the feedback canceller could provide, and caused misadjustment in response to high-level inputs, by biasing adaptive filter coefficients toward lower magnitudes. Cancellation signal clipping mitigated these negative effects, permitting higher amounts of added stable gain and less misadjustment in response to high-level inputs, but the benefit was reduced in the presence of the highest-level inputs.

Adaptive feedback cancellation in hearing aids using a sinusoidal near-end signal model

“…Typically, there exist two approaches to this decorrelation [1], i.e., decorrelation in the closed signal loop and decorrelation in the adaptive filtering circuit. Recently proposed methods for decorrelation in the closed signal loop consist in the insertion of all-pass filters [2] in the forward path of the hearing aid or in clipping [3] of the feedback signal arriving at the microphone. Alternatively, an unbiased identification of the feedback path model can be achieved by applying decorrelation in the adaptive filtering circuit, i.e., by first prefiltering the loudspeaker and microphone signals with the inverse near-end signal model before feeding these signals to the adaptive filtering algorithm [4], [5].…”

Study on the applicability of instrumental measures for black-box evaluation of static feedback control in hearing aids

“…A simple method to detect instability is to track the short-term output-to-reference signal energy ratio ORR(l) 15 ORRðlÞ ¼ 10 log 10…”

“…Since a feedback control system basically permits an increase of the forward path gain without the system becoming unstable, the amount by which this gain can be increased characterizes one aspect of its performance. This increased forward path gain is typically measured in terms of the maximum stable gain (MSG), 2,6,[14][15][16] or the loop gain. 17,18 Alternatively, measures for the detection of instability (and thereby, indirectly, the maximum gain) have been proposed by the authors of Refs.…”

Improved prediction error filters for adaptive feedback cancellation in hearing aids

“…Typically, there exist two approaches to achieve this decorrelation [4], i.e., decorrelation in the closed signal loop and decorrelation in the adaptive filtering circuit. Recently proposed methods for decorrelation in the closed signal loop consist of inserting all-pass filters in the forward path of the hearing aid [5], applying a clipping operation to the feedback signal arriving at the microphone [6], or inserting a probe noise signal into the closed signal loop [7]. However, decorrelation in the closed signal loop implicitly affects the desired (near-end) speech component, hence a trade-off between signal decorrelation and perceptual degradation is unavoidable [4].…”