Feedback Cancellation Research Articles

Effects of kinesthetic and cutaneous stimulation during the learning of a viscous force field.

Haptic stimulation can help humans learn perceptual motor skills, but the precise way in which it influences the learning process has not yet been clarified. This study investigates the role of the kinesthetic and cutaneous components of haptic feedback during the learning of a viscous curl field, taking also into account the influence of visual feedback. We present the results of an experiment in which 17 subjects were asked to make reaching movements while grasping a joystick and wearing a pair of cutaneous devices. Each device was able to provide cutaneous contact forces through a moving platform. The subjects received visual feedback about joystick's position. During the experiment, the system delivered a perturbation through (1) full haptic stimulation, (2) kinesthetic stimulation alone, (3) cutaneous stimulation alone, (4) altered visual feedback, or (5) altered visual feedback plus cutaneous stimulation. Conditions 1, 2, and 3 were also tested with the cancellation of the visual feedback of position error. Results indicate that kinesthetic stimuli played a primary role during motor adaptation to the viscous field, which is a fundamental premise to motor learning and rehabilitation. On the other hand, cutaneous stimulation alone appeared not to bring significant direct or adaptation effects, although it helped in reducing direct effects when used in addition to kinesthetic stimulation. The experimental conditions with visual cancellation of position error showed slower adaptation rates, indicating that visual feedback actively contributes to the formation of internal models. However, modest learning effects were detected when the visual information was used to render the viscous field.

Feedback Cancellation With Probe Shaping Compensation

Adaptive feedback cancellation methods may integrate the use of probe signals to assist with the biased optimal solution in acoustic systems working in closed-loop. However, injecting a probe noise in the loudspeaker decreases the signal quality perceived by users of assistive listening devices. To counter this, probe signals are usually shaped to provide some level of perceptual masking. In this letter we show the impact of using a shaping filter on the system behavior in terms of convergence rate and steady state error. From this study, it can be concluded that shaping the probe signal may have detrimental influence in terms of system performance. Accordingly, we propose to use the unshaped probe signal combined with an inverse filter of the shaping filter to identify the feedback channel. This restructure of the problem restores convergence rate of LMS type algorithms. Furthermore, we also show that an adequate forward path delay is required to obtain an unbiased solution and that the suggested scheme reduces this delay.

Variable step-size affine projection algorithm based on global speech absence probability for adaptive feedback cancellation

A novel approach is proposed for improving adaptive feedback cancellation using a variable step-size affine projection algorithm (VSS-APA) based on global speech absence probability (GSAP). The variable step-size of the proposed VSS-APA is adjusted according to the GSAP of the current frame. The weight vector of the adaptive filter is updated by the probability of the speech absence. The performance measure of acoustic feedback cancellation is evaluated using normalized misalignment. Experimental results demonstrate that the proposed approach has better performance than the normalized least mean square (NLMS) and the constant step-size affine projection algorithms.

64 Bands Hybrid Noise Reduction and Feedback Cancellation Algorithm for Hearing Aid

Both chronic problems of hearing aid have been solved by a probabilistic signal processing algorithm. The algorithm was implemented into a low and single voltage and low power dsp ic chip which can be used as a hybrid of the hearing aid. Both simulated and experimented results show clear noise reduction as well as feedback cancellation. The computational capacity of the physical chip was practically discussed for the limit of the algorithm.

Criteria for estimating an FIR filter for cancelling the feedback path signal in hearing aid system

Many adaptive methods use a Finite Impulse Response (FIR) filter to estimate and cancel the effect of acoustic feedback from the loudspeaker to the microphone in a hearing aid system. In these methods the order of the filter is assumed to be fixed and known a priori, even if the feedback path characteristics change from one environment to another. Underestimation of the order of the filter and thus, the filter itself, results in inadequate feedback cancellation, while overestimation of the filter order increases computational complexity, delay, and power consumption without significantly improving cancellation of the feedback path effect. In this paper an adaptive method using short-duration noise injection with new criteria is proposed to recursively find the FIR filter of proper order for estimating the feedback path and cancelling its effect. The proposed method requires no a priori knowledge of the acoustic feedback path or its order. Using the speech and music signals as the desired signals at the input microphone, the performance of the proposed method is analyzed and compared with those based on the convergence of Misalignment (MISA) and Perceptual Evaluation of Speech Quality (PESQ) criteria.

Effects of imperfect feedback cancellation on the design of AF full-duplex relay system

This paper studies the effects of imperfect feedback cancellation on the design of amplify-and-forward full-duplex relay system. The lower and upper bounds of relay-transmit power as well as the upper bound of a feedback channel estimation error, guaranteeing improved performance than point-to-point transmission, are derived. Then, we propose the strategy controlling relay-transmit power within bounds. The computer simulations confirm the analysis.

Modified Pseudo Affine Projection Algorithm for Feedback Cancellation in Hearing Aids

Modified Pseudo Affine Projection Algorithm for Feedback Cancellation in Hearing Aids

가변 스텝 크기 적응 필터와 음성 검출기를 이용한 보청기용 피드백 제거 알고리즘

Acoustic feedback is perceived as whistling or howling, which is a major complaint of hearing-aids users. Acoustic feedback cancellation is important in hearing-aids because acoustic feedback degrades performance of the hearing aid device by reducing maximum insertion gain. Adaptive systems for estimate acoustic feedback path and feedback suppression algorithms have been proposed in order to solve this problem. A typical feedback cancellation algorithm is LMS(least mean squares) because of its computational efficiency. However it has problem of convergence performance in high correlated input signal. In this paper, we propose a new variable step-size normalized LMS(least mean squares) algorithm using VAD(voice activity detection) to overcome the limitation of the LMS algorithm. The VAD algorithm is GSAP(global speech absence probability) and the feedback cancellation algorithm is normalized LMS. The proposed algorithm applies different step-size between voice and non-voice using VAD, for high stability, fast convergence speed and low misalignment when correlated inputs, such as speech. The result of simulation with white noise mixed speech signal, the proposed algorithm shows high performance then traditional algorithm in terms of stability, convergence speed and misalignment.

ATSC DTV 방송용 중계기 궤환간섭 제거 성능 개선

본 논문에서는 ATSC DTV 시스템에서 독립적인 궤환간섭 제거기(Feedback Interference Canceller: FIC)를 가지는 등화형 디지털 동일채널 중계기(Equalization Digital On-Channel Repeater: EDOCR)의 궤환간섭 제거 성능 향상을 위한 새로운 구조의 FIC를 제안한다. FIC는 기준신호와 궤환되는 신호의 상관관계를 이용하여 궤환채널을 추정하는데, ATSC DTV 방송 신호는 신호의 상관관계 특성을 저해하는 DC 파일럿을 포함하고 있으므로 FIC로 하여금 정확한 궤환채널 추정을 수행하지 못하게 한다. 이러한 문제를 해결하기 위해, EDOCR과 FIC의 결합 구조에 기반하여 EDOCR에서 신호 재변조 시 DC 파일럿을 포함하지 않는 기준신호를 추가적으로 생성하여 궤환채널 추정에 사용하는 DC 파일럿 없는 기준신호 기반 FIC와 디지털 신호처리를 통해 입력신호들을 백색화하여 DC 파일럿을 제거한 후 궤환채널을 추정하는 백색화된 신호 영역 FIC를 제안한다. 모의실험을 통해, 제안된 두 FIC 구조 모두 기존의 상관관계 제거형 FIC에 비해 우수한 궤환간섭 제거 성능을 가짐을 보인다. We propose two feedback interference cancellers(FICs) to improve the performance of the equalization digital on-channel repeater(EDOCR) with the FIC for the ATSC DTV broadcasting system. The FIC estimates the feedback channel between Tx. and Rx. antennas of the repeater by cross-correlating the reference signal and the feedback signal. Since there is a DC pilot which ruins the white property of the ATSC DTV signals, the FIC cannot estimate the feedback channel accurately. To solve the problem, the structural method which uses an additional DC pilot free reference for feedback channel estimation and the algorithmic method based on the digital signal processing which whitens the ATSC DTV signals and performs the feedback cancellation in the whitened signal domain. Simulation results show that the proposed two FICs show better feedback cancellation performance than the conventional FIC.

New Insights Into Optimal Acoustic Feedback Cancellation

In this letter, we present new insights into the bias problem for acoustic feedback cancellation when a probe signal approach is used. The optimum solution of the feedback canceler is not the feedback path but the product of the feedback path and the sensitivity function and hence, the solution is biased. The novelty of this paper also consists of the derivation of the conditions for unbiased feedback cancellation when a probe signal is used as input to the canceler. An adequate delay in the forward path is necessary to reduce, or remove the bias term. The theoretical analysis is verified with simulation results.

Improved prediction error filters for adaptive feedback cancellation in hearing aids

Acoustic feedback is a well-known problem in hearing aids, caused by the undesired acoustic coupling between the hearing aid loudspeaker and microphone. Acoustic feedback produces annoying howling sounds and limits the maximum achievable hearing aid amplification. This paper is focused on adaptive feedback cancellation (AFC) where the goal is to adaptively model the acoustic feedback path and estimate the feedback signal, which is then subtracted from the microphone signal. The main problem in identifying the acoustic feedback path model is the correlation between the near-end signal and the loudspeaker signal caused by the closed signal loop, in particular when the near-end signal is spectrally colored as is the case for a speech signal. This paper adopts a prediction-error method (PEM)-based approach to AFC, which is based on the use of decorrelating prediction error filters (PEFs). We propose a number of improved PEF designs that are inspired by harmonic sinusoidal modeling and pitch prediction of speech signals. The resulting PEM-based AFC algorithms are evaluated in terms of the maximum stable gain (MSG), filter misadjustment, and computational complexity. Simulation results for a hearing aid scenario indicate an improvement up to 5–7dB in MSG and up to 6–8dB in terms of filter misadjustment.

ADAPTIVE LONG-TERM PREDICTION FILTER FOR ADAPTIVE WHITENING

The invention relates to a hearing instrument for processing an input sound to an output sound according to a user's needs. The invention further relates to a method of estimating acoustic feedback in a hearing instrument. The object of the present invention is to reduce the impact of tonal components in the target input signal on the quality of the estimate of acoustic feedback. The problem is solved in that hearing instrument comprises an input transducer for converting an input sound to an electric input signal and an output transducer for converting a processed electric output signal to an output sound, a forward path being defined between the input transducer and the output transducer and comprising a signal processing unit defining an input side and an output side of the forward path, a feedback loop from the output side to the input side comprising a feedback cancellation system for estimating the effect of acoustic feedback from the output transducer to the input transducer, the feedback cancellation system comprising a feedback path estimation unit receiving first and second estimation input signals from the input and output side of the forward path, respectively, wherein the first and second estimation input signal paths comprise first and second long term prediction filters P(z) each having an input and an output, the feedback cancellation system being adapted to provide that the variable parameters of at least one of the long term prediction filters are estimated based on the input signal to the filter in question. Embodiments of the invention have the advantage of leading to better feedback cancellation, even for tonal input signals. The invention may e.g. be used for the hearing instruments or headsets.

METHOD FOR SUPPRESSING ACOUSTIC FEEDBACK IN A HEARING DEVICE AND CORRESPONDING HEARING DEVICE

A hearing device (HD) incorporates a method for adaptive cancellation of acoustic feedback (AF). The method comprises generating an estimated feedback signal (EF) and subtracting the estimated feedback signal (EF) from the microphone signal (MS) before feeding it to a signal processor (SP) providing the primary hearing device function. The estimated feedback signal (EF) is generated in an adaptive filter (FE1), which is controlled using a least-mean-square algorithm, which operates on an error signal (E) and a reference signal (R). The algorithm may behave erroneously if the feedback path changes while a signal with low HF content, such as speech, is received. In this case, the hearing device (HD) will not be able to quickly adapt the HF characteristic of the adaptive filter (FE1) to the changed conditions. The adaptive filter (FE1) may thus have an incorrect HF gain when a subsequent signal with high HF content is received. This may lead to whistling or, alternatively, to an unwanted suppression of the subsequent signal. The problem is solved by modifying a filter function (H) applied to the error signal (E) and to the reference signal (R) in dependence on estimated relative amounts of high- and low-frequency signal content in the microphone signal (MS).

Adaptive Feedback Cancellation on Improved DCD Algorithms

Adaptive Feedback Cancellation on Improved DCD Algorithms

Novel Acoustic Feedback Cancellation Approaches in Hearing Aid Applications Using Probe Noise and Probe Noise Enhancement

Adaptive filters are widely used in acoustic feedback cancellation systems and have evolved to be state-of-the-art. One major challenge remaining is that the adaptive filter estimates are biased due to the nonzero correlation between the loudspeaker signals and the signals entering the audio system. In many cases, this bias problem causes the cancellation system to fail. The traditional probe noise approach, where a noise signal is added to the loudspeaker signal can, in theory, prevent the bias. However, in practice, the probe noise level must often be so high that the noise is clearly audible and annoying; this makes the traditional probe noise approach less useful in practical applications. In this work, we explain theoretically the decreased convergence rate when using low-level probe noise in the traditional approach, before we propose and study analytically two new probe noise approaches utilizing a combination of specifically designed probe noise signals and probe noise enhancement. Despite using low-level and inaudible probe noise signals, both approaches significantly improve the convergence behavior of the cancellation system compared to the traditional probe noise approach. This makes the proposed approaches much more attractive in practical applications. We demonstrate this through a simulation experiment with audio signals in a hearing aid acoustic feedback cancellation system, where the convergence rate is improved by as much as a factor of 10.

Efficient OFDM-based WLAN-multicast with feedback aggregation, power control and rate adaptation

Feedback aggregation is an approach for repeat request protocols in which positive and negative feedback from multiple wireless stations is aggregated within a single time slot, during which negative acknowledgments (NACKs) from non-leader receivers may cancel positive acknowledgments (ACK) sent by the leader. This solves the problem of increased overhead with increasing number of receivers, and enables high rate audiovisual mediacast for large wireless multicast receiver groups. In this paper, we investigate feedback cancelation (jamming) failure rates, which in turn determine the performance of error correction protocols using feedback aggregation. We do so by simulation and measurement using a variable number of NACKs in i.i.d. fading scenarios. Our results apply to OFDM based wireless multicast and we show that multicast error performance and throughput can be tuned with ACK power control using consumer IEEE 802.11 hardware.

Correlation Canceling-Type Feedback Canceler Based on Decision-Directed Pilot Symbols for T-DMB Repeaters

This paper presents a novel correlation canceling-type feedback canceler based on decision-directed pilot symbols for a terrestrial digital multimedia broadcasting (T-DMB) on-channel repeater (OCR). In order to guarantee an additional isolation of the OCR, two types of the feedback cancelers have been investigated: a correlation canceling (CC)-type feedback canceler and a frequency-domain channel estimation (FDCE)-type feedback canceler. While both of the feedback cancelers suppress the feedback signal effectively, they can operate complementarily each other with their own respective advantages. To achieve these complementary properties of the two types of feedback cancelers, we adopt a CC-type feedback canceling structure based on the frequency-domain estimated pilot symbols. The proposed feedback canceler improves the feedback channel estimation accuracy of the conventional CC-type feedback canceler as well as increases the channel estimation speed of the conventional FDCE-type feedback canceler. Simulation results show that the proposed feedback canceler has better feedback canceling performance and tracking ability for dynamic feedback channels.

An Adaptive Feedback Canceller for Full-Duplex Relays Based on Spectrum Shaping

Although full-duplex relaying schemes are appealing in order to improve spectral efficiency, simultaneous reception and transmission in the same frequency results in self-interference, distorting the retransmitted signal and making the relay prone to oscillation. Current feedback cancellation techniques by means of adaptive filters are hampered by the fact that the useful and interference signals are highly correlated. We present a new adaptive algorithm which effectively and blindly restores the spectral shape of the desired signal. In contrast with previous schemes, the novel adaptive feedback canceller has low complexity, does not introduce additional delay in the relay station, and partly compensates for multipath propagation.

Objective Prediction of the Sound Quality of Music Processed by an Adaptive Feedback Canceller

Adaptive feedback cancellers in hearing aids can produce unpleasant sounding distortion artifacts (entrainment) in response to periodic inputs, including music. Reliable objective metrics that predict user-perceived distortion could significantly reduce development costs for new hearing aids. The aim of this study was to gain insight into the ability of different objective metrics to predict subjective ratings of the sound quality of music processed by adaptive feedback cancellation. The metrics tested consisted of perceptual measures from established audio quality models (including Perceptual Evaluation of Audio Quality (PEAQ), PEMO-Q and .Rnonlin). Neural networks were used to map between the values of the perceptual measures and a subjective scale of perceived quality. Training data consisted of values of perceptual measures obtained from ten different excerpts of orchestral music processed by a simplified model of a hearing aid with an adaptive feedback canceller, and corresponding subjective quality ratings from 27 normal hearing subjects. An optimal combination of perceptual measures to use as inputs to a network input was found using an extended Fourier amplitude sensitivity test (EFAST). Our results suggest that the most salient inputs to a multivariate model of measured quality ratings consist of perceptual measures related to spectral noise loudness, modulation differences between clean and processed signals, and correlation-based measurement of nonlinear distortion. The intraclass correlation between mean subjective ratings and the output of a network combining these perceptual measures was high , which compares favorably to results from previous studies of perceptual quality metrics applied to audio signals with other forms of noise or distortion.

On Acoustic Feedback Cancellation Using Probe Noise in Multiple-Microphone and Single-Loudspeaker Systems

A probe noise signal can be used in an acoustic feedback cancellation system to prevent biased adaptive estimation of acoustic feedback paths. However, practical experiences and simulation results indicate that whenever a low-level and inaudible probe noise signal is used, the convergence rate of the adaptive estimation is significantly decreased when keeping the steady-state error unchanged. The goal of this work is to derive analytic expressions for the system behavior such as convergence rate and steady-state error for a multiple-microphone and single-loudspeaker audio system, where the acoustic feedback cancellation is carried out using a probe noise signal. The derived results show how different system parameters and signal properties affect the cancellation performance, and the results explain theoretically the decreased convergence rate. Understanding this is important for making further improvements in the existing probe noise approach.