Online Censoring Based Acoustic Feedback Cancellation for Wearable Hearing Aids

When fitting hearing aids, there are three guidelines that should always be followed by the dispenser: restore audibility; so that the amplified sound is above the user's threshold, limit the output; so that the amplified signal does not exceed the user's discomfort level, and do no harm; so that the amplified signal is not unintentionally or undesirably altered by the hearing aid. The first two of these three guidelines are obvious. The first is to present sounds above the user's threshold of hearing in order to create an acoustic environment with the maximum amount of audible speech cues. The second ensures that discomfort level is not exceeded, so that the user does not wince or remove the hearing aids when loud sounds are present. The third guideline—do no harm—is less obvious. This indicates that it is important that the hearing aids produce no alteration of the signal other than that which the fitter intends. This is a subtle way of saying that, among other things, well-fitted hearing aids should not distort the desired sound. The topic of distortion is the subject of this issue of Trends in Amplification. The intention of this issue is to explain why distortion occurs in some hearing aids; to explain how distortion is measured; to summarize what can be done to prevent distortion; and to summarize the perception of distortion by the hearing aid wearer. Distortion in hearing aids can be broadly defined as the generation of undesired audible components that are present in the output, but which are not present in the input. When distortion occurs, hearing aids produce undesired elements at the output through the interaction of the processed signal with some internal non-linear mechanism. These undesired components may interfere to some degree or other with the reception of sound by the listener. If these added elements are small compared to the overall signal level, they may effectively cause no interference at all. If they are large, they can be so disruptive to the listener that the desired sound becomes irritating or even incomprehensible. All audio systems inevitably contain some amount of distortion. The practical problem for the listener is the type of distortion that is present and the level that is acceptable or tolerable in hearing aids before the distortion becomes disruptive to speech intelligibility and sound quality. It is known that highly distorted speech in quiet can remain intelligible (Licklider, 1946); however, as dispensers often experience, intelligibility is not the only measure of whether or not a user will accept and wear hearing aids. Gabrielsson and Sjogren (1979b) have shown that overall perceived sound quality is important to users when selecting a hearing aid. Punch (1978) has shown that listeners with mild to moderate sensorineural hearing losses retain the same ability to make distinctions in sound quality judgments as listeners with normal hearing. This implies that good sound quality is as equally important and desired by listeners with a hearing impairment as it is for listeners with normal hearing. Three characteristics of distortion in hearing aids modify the sound delivered to the user: the type of distortion, the relative amount of distortion at different frequencies, and the variation of distortion with different input levels. Since the most important goal for fitting hearing aids is to restore or facilitate communication ability, undistorted sound is important for optimum speech intelligibility and sound quality. However, it is important to also recognize that there are other reasons to provide undistorted amplification of sound. For example, undistorted and pleasant reproduction of music may be an important sensory experience for some listeners. This issue concentrates on different types of undesired modification to the waveshape of the sound, primarily by total harmonic distortion (THD) and intermodulation distortion (IMD). However, in a more general sense, any undesired component added to the sound by hearing aids is a form of distortion. Thus, this issue also discusses sound generated by hearing aids with no signal present at the microphone. This artifact is more commonly called internal noise. Internal noise fits within the definition of distortion given earlier, since internal noise is an undesired product generated in the output of hearing aids that is not present at the input. In some cases, distortion and internal noise are so closely linked that they cannot always be separated into discrete entities. For example, instability in the frequency and shape of the clock pulses in a Class D output stage (often loosely called clock jitter) results in distortion of the signal. However, this artifact may be audibly revealed in the output sound primarily as noise, rather than as distortion of the waveform. According to this broad definition of distortion, undesired noises such as “motorboating” and other acoustic feedback oscillations can also be considered to be forms of distortion. However, acoustic feedback and other similar audible artifacts occurring within hearing aids will not be discussed here. These types of distortion have been discussed in detail by Agnew (1996b) in a previous issue of Trends in Amplification. In this issue distortion is discussed in two general categories: Undesired modification of the waveform of the incoming sound by some mechanism occurring within the hearing aids. The severity of this effect may or may not vary with the acoustic level of the incoming sound. This type of audible artifact is generally what most dispensers refer to as “distortion”. This will be the subject of Part I of this issue, and will follow the definition used for distortion in this text. The production of undesired audible components in the output sound, regardless of whether or not there is any acoustic input to the hearing aid. This is generally called “noise”. This will be the subject of Part II of this issue. The first part of this issue discusses the causes and effect of distortion. First, different types of distortion are described, followed by an explanation of how they are measured. This is followed by a discussion of the sources of distortion that may be present in hearing aids and the various mechanisms by which distortion is created. The final section of Part I discusses the effects of distortion on the hearing aid wearer. For the reader having difficulty understanding the technical concepts in the first part of this tutorial, a good overview from a different perspective has been presented by Kuk (1996). The second part of this issue discusses the causes and effects of internal noise in hearing aids. This part starts with a discussion of sources of internal noise and continues with a description of methods for the measurement of internal noise. This part concludes with a discussion of the perception of internal noise and its effects on the user of hearing aids. At the end of the text is an intentionally long list of references, which is intended to serve as a reasonably comprehensive resource for the reader seeking further information on distortion and noise in hearing aids.

While several proactive acoustic feedback (Larsen-effect) cancellation schemes have been presented for speech applications with short acoustic feedback paths as encountered in hearing aids, these schemes fail with the long impulse responses inherent to, for instance, public address systems. We derive a new prediction error method (PEM)-based scheme (referred to as PEM-AFROW) which identifies both the acoustic feedback path and the nonstationary speech source model. A cascade of a short- and a long-term predictor removes the coloring and periodicity in voiced speech segments, which account for the unwanted correlation between the loudspeaker signal and the speech source signal. The predictors calculate row operations which are applied to prewhiten the speech source signal, resulting in a least squares system that is solved recursively by means of normalized least mean square or recursive least squares algorithms. Simulations show that this approach is indeed superior to earlier approaches whenever long acoustic channels are dealt with

Purpose: This study investigates the social support in both elderly who wear hearing aids and elderly who do not report any hearing loss.Methods: The study subjects were 48 seniors age 65 or older who wore hearing aids and 48 seniors who did not wear hearing aids. A Lubben social network scales survey was conducted. The Korean Version of International Outcome Inventory for Hearing Aids, Puretone Audiometry, and Word Recognition Score tests were carried out on the elderly who were wearing hearing aids.Results: A statistical analysis represented that the total social support scores were not significantly different between the two groups. Of all the social support factors, social network was statistically significant between the groups (p < 0.05), but social support was not statistically significant. The correlation between social support and the degree of hearing loss was not statistically significant. Further, there were no significant relationships found for the social support of older adults’ wearing hearing aids and satisfaction with hearing overall, and the level of social support.Conclusion: The results of the study indicated that users hearing aid users have a smaller social network than those who do not wear hearing aids. However, this result can be interpreted as an independent factor regarding satisfaction with hearing aid use and the degree of hearing. As a follow-up study, it will be necessary to proceed to study the diversity of the background factors for those elderly who do have hearing loss.

In this paper we propose a new variable step-size of the Least-Mean-Square (LMS) algorithm for reducing acoustic feedback in hearing aids. The new variable step-size is designed to approximate the optimum variable step-size that allows the LMS algorithm to decrease its mean-squared error with the fastest rate. The performance of the proposed variable step-size on the acoustic feedback cancellation is compared via computer simulation with those of three other step-size adjustment methods. The comparisons indicate that the new step-size adjustment method has better dynamic and steady state performances than the other methods. In addition, the computation complexity of the new method is relatively low compared with those of the other methods, rendering it more suitable for solving acoustic feedback in hearing aids.

For many people, the use of assistive technologies enhances their quality of life by augmenting their diminishing capabilities. However, some challenges with the design features cause users to reject or abandon their devices. Indeed, little attention is given to the psychological and social needs of users in the design of hearing aids, which are primarily developed according to a function-oriented medical model of disability. While the design of hearing aids has improved through technological advances such as miniaturization, there is limited design research about the emotional needs and meaningful experiences of hard-of-hearing people regarding their devices, which may lead to product abandonment. This research applies a human-centered design approach to explore users’ attitudes and experiences toward visible and expressive hearing aid designs. It seeks to understand how to create emotionally engaging and meaningful devices through design research methods. It applies an exploratory research design strategy including four studies that successively build on one another. This research contributes step-by-step tools/templates for gathering user's explicit knowledge, tacit ideas and latent needs leading to some design recommendations, criteria, and insights for the design of hearing aids. The findings suggest the importance of physical functional and aesthetic aspects of hearing aids in satisfying users’ social and psychological needs. Participants feel that a stigma is associated with the appearance of their hearing devices, and many do not find their current devices stylish, attractive, or unique. Expressive visual features could reduce stigma and enable those who like visibility to openly express themselves. Most participants have positive attitudes toward the examples of expressive visual-changing features in hearing aids. This dissertation offers the following contributions: a framework for long-term emotional attachment with assistive wearables, a human-centered design research framework with a set of tools/templates for collecting user data, an approach to data analysis, insights into the hard-of-hearing population, and a set of criteria for designing hearing aids for them.

Intervention for a Child with Auditory Neuropathy/Dys-synchrony

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.

Publication in the conference proceedings of EUSIPCO, Antalya, Turkey, 2005

Children who wear hearing aids may be at risk for further damage to their hearing from overamplification. Previous research on amplification-induced hearing loss has included children using linear amplification or simulations of predicted threshold shifts based on nonlinear amplification formulae. A relationship between threshold shifts and the use of nonlinear hearing aids in children has not been empirically verified. The purpose of the study was to compare predicted threshold shifts from amplification to longitudinal behavioral thresholds in a large group of children who wear hearing aids to determine the likelihood of amplification-induced hearing loss. An accelerated longitudinal design was used to collect behavioral threshold and amplification data prospectively. Two-hundred and thirteen children with mild-to-profound hearing loss who wore hearing aids were included in the analysis. Behavioral audiometric thresholds, hearing aid outputs, and hearing aid use data were collected for each participant across four study visits. Individual ear- and frequency-specific safety limits were derived based on the Modified Power Law to determine the level at which increased amplification could result in permanent threshold shifts. Behavioral thresholds were used to estimate which children would be above the safety limit at 500, 1000, 2000, and 4000 Hz using thresholds in dB HL and then in dB SPL in the ear canal. Changes in thresholds across visits were compared for children who were above and below the safety limits. Behavioral thresholds decreased across study visits for all children, regardless of whether their amplification was above the safety limits. The magnitude of threshold change across time corresponded with changes in ear canal acoustics as measured by the real-ear-to-coupler difference. Predictions of threshold changes due to amplification for children with hearing loss did not correspond with observed changes in threshold over across 2-4 yr of monitoring amplification. Use of dB HL thresholds and predictions of hearing aid output to set the safety limit resulted in a larger number of children being classified as above the safety limit than when safety limits were based on dB SPL thresholds and measured hearing aid output. Children above the safety limit for the dB SPL criteria tended to be fit above prescriptive targets. Additional research should seek to explain how the Modified Power Law predictions of threshold shift overestimated risk for children who wear hearing aids.

Objective To investigate older and younger adults’ perceptions of older and younger adults who wear hearing aids. Design Participants completed two Implicit Association Tests: One with images of older adults (OA-IAT) and one with images of younger adults (YA-IAT), either wearing or not wearing hearing aids. Participants also rated age, attractiveness, and intelligence of younger and older adults pictured with or without a hearing aid. Study sample Thirty older adults (M age = 70 years, SD = 4.38) and 30 younger adults (M age = 23 years, SD = 3.01) who reported not having hearing aids or a diagnosed hearing impairment. Results For both IATs, older and younger participants responded faster and more accurately when images of individuals wearing hearing aids were paired with negative words in comparison to positive words. Photo ratings did not vary in relation to the presence or absence of hearing aids for either age group. Conclusion Although the photo rating tasks indicate neutral explicit attitudes towards individuals who wear hearing aids, our interpretation of the IAT results indicates that younger and older adults may hold negative implicit attitudes towards both older and younger hearing aid users.

The Independent Hearing Aid Fitting Forum (IHAFF) protocol was developed between 1993 and 1994 during numerous weekend meetings in Denver, Tampa, Anaheim and Chicago. The protocol was the brainchild of Dennis Van Vliet and Michael Marion, who were frustrated by the gap between the ever-evolving technology and the tools available for selecting, fitting and verifying the performance of hearing aids. As clinicians, they were concerned that there was a general lack of knowledge on how to appropriately determine if their patient was a better candidate for wide dynamic range compression, compression limiting, or compression in which the compressor is activated at an intermediate level. Further, they were concerned about the decisions that clinicians were being asked to make everyday which did not need to be made just a few years ago. For example, how to appropriately adjust the compression ratio (CR), compression kneepoint (KP), release time or output in one or more channels. In addition, they were concerned that the present prescriptive formulas, which are appropriate when fitting linear hearing aids, are not appropriate when fitting hearing aids with nonlinear signal processing. Finally, Dennis and Michael did not see any activity when attending professional meetings or reading professional journals which gave them any hope that relief for their concerns was forthcoming. Due to these concerns, Michael and Dennis believed that it was necessary to gather colleagues together who might be able to develop a protocol to help clinicians better serve their patients when dispensing hearing aids containing both linear and nonlinear signal processing. The members of the IHAFF committee were Lucille Beck, Ruth Bentler, Robyn Cox, David Fabry, Gail Gudmundsen, David Hawkins, Mead Killion, Michael Marion, Gus Mueller, Larry Revit, Michael Valente and Dennis Van Vliet. Margo Skinner was an early member of the committee but had to leave because of other commitments. As the reader can imagine, the discussions at these meetings were stimulating, challenging, intriguing, heated and controversial. Numerous fitting and verification strategies were discussed and discarded for a variety of reasons. For example, early discussions centered around referencing all measurements (threshold and loudness judgments) to dB SPL near the eardrum (i.e., SPL-O-GRAM). However, this idea was dropped because equipment was not available to perform these tasks in a clinically efficient manner at the time of the discussions. As the reader knows, such equipment is now available (i.e., the Madsen Auracle, Etymonic Design's AudioScan, Starkey Pro-Connect, ReSound's Real Ear Loudness Mapping (RELM) and Frye real ear analyzers). Discussions were also especially prolonged around the issue of “predicting” loudness judgments from threshold as opposed to individual measurement of loudness judgments. The final IHAFF protocol requires individual measurement of loudness scaling. Important considerations such as counseling, fine-tuning, aural rehabilitation, assistive listening devices, directional microphones, remote controls or digital volume controls were discussed, but it was decided not to include these issues in the final document. The result of those meetings, phone calls, faxes and e-mail messages is the IHAFF protocol. The primary goal of the IHAFF protocol is to “normalize” the loudness experiences of the hearing-impaired patient. Specifically, the goals of the IHAFF protocol are: Sounds judged as “soft” by a normal listener should be audible and judged as “soft” by a hearing-impaired listener who is wearing hearing aids. Sounds judged as “comfortable” by a normal listener should be judged as “comfortable” by a hearing-impaired listener who is wearing hearing aids. Sounds judged as “loud” by a normal listener should be judged as “loud”, but not “uncomfortably loud” by a hearing-impaired listener who is wearing hearing aids. Also, to prevent amplified sounds from exceeding the user's uncomfortable loudness level (LDL). Typically for a cochlear-impaired listener, the use of compression and more than one processing channel will be needed to reach these goals. That is, less gain would be supplied at the higher input levels (compression) if the patient exhibits loudness recruitment, and greater compression might well be needed in the high frequency region where typically the dynamic range between threshold and UCL is reduced in comparison to the dynamic range in the low frequency region. This issue of Trends in Amplification is dedicated to providing the reader with a better knowledge of how to implement the IHAFF protocol. The manuscript is divided into two sections. The first section describes, in detail, how to operate the software that has been developed to assist the user to implement the IHAFF protocol. The second section illustrates the implementation of the IHAFF protocol by “walking through” the entire process with one of our patients.

Previous studies have demonstrated that cortical auditory-evoked potentials (CAEPs) can be reliably elicited in response to speech stimuli in listeners wearing hearing aids. It is unclear, however, how close to the aided behavioral threshold (i.e., at what behavioral sensation level) a sound must be before a cortical response can reliably be detected. The purpose of this study was to systematically examine the relationship between CAEP detection and the audibility of speech sounds (as measured behaviorally), when the listener is wearing a hearing aid fitted to prescriptive targets. A secondary aim was to investigate whether CAEP detection is affected by varying the frequency emphasis of stimuli, so as to simulate variations to the prescribed gain-frequency response of a hearing aid. The results have direct implications for the evaluation of hearing aid fittings in nonresponsive adult clients, and indirect implications for the evaluation of hearing aid fittings in infants. Participants wore hearing aids while listening to speech sounds presented in a sound field. Aided thresholds were measured, and cortical responses evoked, under a range of stimulus conditions. The presence or absence of CAEPs was determined by an automated statistic. Participants were adults (6 females and 4 males). Participants had sensorineural hearing loss ranging from mild to severe-profound in degree. Participants' own hearing aids were replaced with a test hearing aid, with linear processing, during assessments. Pure-tone thresholds and hearing aid gain measurements were obtained, and a theoretical prediction of speech stimulus audibility for each participant (similar to those used for audibility predictions in infant hearing aid fittings) was calculated. Three speech stimuli, (/m/, /t/, and /g/) were presented aided (monaurally, nontest ear occluded), free field, under three conditions (+4 dB/octave, -4 dB/octave, and without filtering), at levels of 40, 50, and 60 dB SPL (measured for the unfiltered condition). Behavioral thresholds were obtained, and CAEP recordings were made using these stimuli. The interaction of hearing loss, presentation levels, and filtering conditions resulted in a range of CAEP test behavioral sensation levels (SLs), from -25 to +40 dB. Statistically significant CAEPs (p < .05) were obtained for virtually every presentation where the behavioral sensation level was >10 dB, and for only 5% of occasions when the sensation level was negative. In these ("false-positive") cases, the greatest (negative) sensation level at which a CAEP was judged to be present was -6 dB SL. CAEPs are a sensitive tool for directly evaluating the audibility of speech sounds, at least for adult listeners. CAEP evaluation was found to be more accurate than audibility predictions, based on threshold and hearing aid response measures.

Acoustic feedback in hearing aids occurs due to the coupling between the hearing aid loudspeaker and microphones. In order to reduce acoustic feedback, adaptive filters are often used to estimate the feedback path. To increase the convergence speed and decrease the computational complexity of the adaptive algorithms, it has been proposed to split the acoustic feedback path into a time-invariant fixed part and a time-varying variable part. A key question of this approach is how to determine the fixed part. In this paper, two approaches are investigated: (1) a digital filter design approach that makes use of the signals of at least two hearing aid microphones and (2) a defined physical location approach using an electro-acoustic model and the signals of one hearing aid microphone and an additional ear canal microphone. An experimental comparison using measured acoustic feedback paths showed that both approaches enable one to reduce the number of variable part coefficients. It is shown that individualization of the fixed part increases the performance. Furthermore, the two approaches offer solutions for different requirements on the effort to a specific hearing aid design on the one hand and the effort during the hearing aid fitting on the other hand.

Purpose: The present study examines auditory training outcomes in terms of speech perception in noise, working memory, reasoning ability, and subjective hearing aid satisfaction. Methods: Ten older adults who wear hearing aids (mean age: 71.6) voluntarily participated in the study. For the training material, 78 sentence sets composed of 3 to 5 sentences were used. During the auditory training, participants tried to remember the order of sentences. Among the 78 sentence sets, 45 contained clues and the rest did not. Each participant underwent assessments including speech perception in noise and digit spans and reasoning test and completed a self-report hearing aid satisfaction questionnaire both pre- and post-auditory training. The participants completed eight sessions of the auditory training. Results: The results showed a statistically significant increase in speech recognition ability in noise, short-term memory, and working memory, as well as satisfaction with hearing aid use. Despite a slight increase on the reasoning test, there was no statistically significant improvement.Conclusion: The results of this study suggested that the auditory training in remembering the order of sentences improved speech perception in noise, sensory and working memory, and subjective satisfaction with hearing aids. Future research can investigate more effective auditory training tools to improve the various cognitive skills and communication ability of older adults who wear hearing aids.

Affine projection algorithms (APA) have been widely employed for acoustic echo cancellation (AEC) since they provide a natural trade-off between convergence speed and computational complexity. However, their application in Acoustic Feedback Cancellation (AFC) in hearing aids so far has been limited due to lack of performance improvement in one microphone settings. A two microphone technique was recently proposed to provide an improved cancellation for a larger class of input signals. This paper proposes to use APA in the two microphone closed-loop feedback cancellation. It is shown that APA has significantly improved the misalignment and maximum stable gain of the system. Moreover, a new variable Gaussian step-size control (VGSS) for APA is also proposed. The simulation results indicate an improvement in convergence speed of the proposed algorithms as compared to previously suggested methods.