H. Gustav Mueller

The Effects of Digital Noise Reduction on the Acceptance of Background Noise

Modern hearing aids commonly employ digital noise reduction (DNR) algorithms. The potential benefit of these algorithms is to provide improved speech understanding in noise or, at the least, to provide relaxed listening or increased ease of listening. In this study, 22 adults were fitted with 16-channel wide-dynamic-range compression hearing aids containing DNR processing. The DNR includes both modulation-based and Wiener-filter-type algorithms working simultaneously. Both speech intelligibility and acceptable noise level (ANL) were assessed using the Hearing in Noise Test (HINT) with DNR on and DNR off. The ANL was also assessed without hearing aids. The results showed a significant mean improvement for the ANL (4.2 dB) for the DNR-on condition when compared to DNR-off condition. Moreover, there was a significant correlation between the magnitude of ANL improvement (relative to DNR on) and the DNR-off ANL. There was no significant mean improvement for the HINT for the DNR-on condition, and on an individual basis, the HINT score did not significantly correlate with either aided ANL (DNR on or DNR off). These findings suggest that at least within the constraints of the DNR algorithms and test conditions employed in this study, DNR can significantly improve the clinically measured ANL, which may result in improved ease of listening for speech-in-noise situations.

Amplification With Digital Noise Reduction and the Perception of Annoying and Aversive Sounds

Hearing aid users report difficulties using their hearing aids in noisy environments. Problems include understanding speech, loudness discomfort, and annoyance with background noise. Digital noise reduction algorithms have been promoted as a method to solve speech understanding and comfort in noise problems. Research has failed to find improved speech understanding in noise. Little is known about how digital noise reduction affects noise annoyance and aversiveness. The goals of this investigation were to determine how a specific digital noise reduction system affects hearing aid users’ perception of noise annoyance and aversiveness and to compare their perceptions to those of normal-hearing listeners. Ratings of noise annoyance and of aversiveness were obtained from 49 participants with moderate sensorineural hearing loss before fitting and after 3 weeks of hearing aid use. Findings were compared to measures obtained from normal-hearing listeners. Perceived annoyance and aversiveness increased with amplification. Annoyance and aversiveness with the hearing aid approximated normal perception. The results of this investigation suggest the need for counseling patients about realistic expectations related to annoyance and aversiveness of sounds at the time of hearing aid fitting.

Survey examines popularity of real-ear probe-microphone measures

It was in 1979, at the International Ear Clinics’ Symposium, that Earl Harford, PhD, first described a new technique to assess the performance of hearing aids by putting a microphone in the ear canal so that actual realear gain and output could be measured. Many believed that the “science” component of fitting hearing aids had finally arrived. By the mid-1980s, leading audiologists were predicting that real-ear probe-microphone measures would be used by nearly everyone by the end of the decade. But that didn’t happen. In fact, it didn’t happen in the ‘90s or in the ‘00s either, despite Best Practice Guidelines, such as those of the American Academy of Audiology (AAA), stating: “Prescribed gain (output) from a validated prescriptive method should be verified using a probe-microphone approach that is referenced to ear canal SPL.” That’s a pretty unambiguous statement. Here at HJ, we’ve periodically sampled the use of real-ear probe-mic measures through dispenser surveys. For example, in 1995 we found that “routine” use of these measures was reported by 54% of audiologists (n=134) and 18% of hearing instrument specialists (HISs; n=108), with an overall use rate of 39%. In 1999, we examined use rates for both groups, but limited it to those who owned or had access to the equipment. Even then, only 42% reported routine use. Our 2003 survey showed an overall use rate of 37% (n=558 audiologists, 49 HISs). And finally, in a 2005 survey, we again examined the popularity of these measures, this time just among audiologists. The overall use rate was 34%. It was slightly higher (~40%) for recent graduates (either masters or AuDs) and for experienced audiologists who had obtained their AuD through distance learning. For some reason, or probably for many related reasons, using real-ear probe-mic measures for verification of hearing aid performance has never become the prevailing practice. Our past surveys suggest that only about 1/3 of dispensers have been using this verification approach routinely, with no meaningful upward trend observed.

Open-canal fittings: Ten take-home tips

Fitting hearing aids involves innovation and compromise. This is especially true in deciding the tightness of the fit, whether of an earmold or a custom product. Tight-fitting instruments are good for obtaining high levels of gain and output, especially in the lower frequencies, and for minimizing feedback problems. However, they often are uncomfortable, sometimes create an unacceptable occlusion effect, and can give the patient a “plugged up” sensation. If the patient has normal or near-normal hearing in the lower frequencies, it is common practice to move toward a more open fitting to alleviate occlusion and let low frequencies into the ear naturally. In this case, the compromise is reduced gain and output, and a greater chance of unwanted acoustic feedback. There is little documentation of the first open-canal (OC) fittings, but we know they received considerable attention immediately after the CROS-type hearing aid was introduced.1 It was quickly discovered that the open earpieces (or tubing only) used for the CROS hearing aid also could be used for ipsilateral high-frequency amplification (hence, the term IROS [ipsilateral routing of signals], referring to a large vent). In the late 1960s, researchers showed that OC fittings could provide useful high-frequency amplification.2-4 In the ensuing decades, there wasn’t much excitement about open fittings, though there was some renewed interest during the Libby horn’s peak of popularity5 and on other occasions when a product designed specifically for high-frequency hearing loss was introduced.6 The ho-hum attitude toward OC fittings that persisted for more than 30 years was stirred up considerably a few years ago when five key aspects were combined in a single OC product: a small “cute” BTE casing, multichannel compression and gain adjustments, a thin tube channeling the sound from the hearing aid to the ear, a comfortable nonoccluding eartip, and, most importantly, effective feedbackreduction algorithms. As reviewed by Mueller,7 these five factors combine to offer a wide range of potential patient benefits, and OC products have rapidly taken over a sizable share of the total hearing aid market. While the peer-reviewed journals have published little about these modern OC fittings, several articles about this style have appeared in the trade journals, and the OC product is a hot topic at hearing aid workshops and seminars. However, there are still some key issues related to these products that need further clarification, and maybe even a couple areas where misconceptions exist. In this paper, we’ll provide some tips on OC fittings, which we hope will clarify more than they confuse.

Prescribing maximum hearing aid output: Differences among manufacturers found

It seems that just about every month we read about some new advance in hearing aid technology. The practitioners dispensing these instruments must continually make decisions concerning what type of digital noise reduction, directional technology, or Bluetooth applications are best for their patients. Hearing aid fitting and verification also seem to be constantly changing. We now have new prescriptive methods for both the DSL and the NAL, and real speech has become a routine input signal for probe-microphone measurements. But one thing has pretty much stayed the same: selecting the appropriate maximum output for each patient. We still usually limit the output by adjusting the AGCo kneepoint, technology that has been available since the 1940s. And, if we don’t get it right, we often have an unhappy hearing aid user. That probably hasn’t changed in the last 60 years either.

Clinical evaluation of a new hearing aid anti-cardioid directivity pattern

Abstract Objective: The purpose of this research was to evaluate a new directional hearing aid algorithm which automatically adapts to an anti-cardioid pattern in background noise when a speech signal originates from behind the hearing aid user. Design: Using the hearing-in-noise-test (HINT) in the soundfield, with the sentences delivered adaptively from the back (180°) and the standard HINT competing noise from the front (0°; 72 dB SPL), the participants were tested for three different hearing aid conditions: omnidirectional, conventional adaptive directional, and adaptive directional with the anti-cardioid algorithm enabled. Study Sample: Adults (n = 21) with bilaterally symmetrical downward sloping sensorineural hearing loss; experienced hearing aid users and aided bilaterally for experimental testing. Results: Results revealed a significant effect for the hearing aid microphone setting (p < .0001), with a HINT mean RTS of 4.2 dB for conventional adaptive directional, −0.1 dB for omnidirectional, and −5.7 dB when the anti-cardioid algorithm was active. This was a large effect size (Cohens f2). Conclusion: The findings suggest that the signal classification system steered the algorithm correctly, and that when implemented, the anti-cardioid polar pattern resulted in an improvement in speech recognition in background noise for this listening situation. Sumario Objetivo: El propósito de esta investigación fue evaluar un nuevo algoritmo para auxiliares auditivos direccionales que se adapta automáticamente a un patrón anti-cardioide en ruido de fondo cuando una señal de lenguaje se origina detrás del usuario de un auxiliar auditivo. Diseño: Usando la prueba de audición-en-ruido (HINT), en campo libre, con oraciones enviadas adaptativamente desde atrás (180°) y el HINT estándar con ruido competitivo desde el frente (0°; 72 dB SPL), los participantes fueron evaluados en tres diferentes condiciones de escucha: omnidireccional, direccional adaptativa convencional y adaptativa direccional con el algoritmo anti-cardioide habilitado. Muestra de estudio: Adultos (n = 21) con pérdida auditiva bilateral simétrica, sensorineural, de perfil descendente, con experiencia en el uso de auxiliares auditivos y con adaptación bilateral para la prueba experimental. Resultados: Los resultados revelaron un efecto significativo para el ajuste del micrófono del auxiliar auditivo (p < .0001), con una HINT media y RTS de 4.2 dB para la forma direccional convencional adaptativa, −0.1 dB para la omnidireccional y −5.7 dB cuando se habilitóel algoritmo anti-cardioide. Este fue un efecto de gran envergadura (Cohens f2). Conclusión: Los hallazgos sugieren que el sistema de clasificación de señales conducen el algorritmo correctamente y que cuando es habilitado, el patrón polar anti-cardioide determina una mejoría en el reconocimiento del lenguaje con ruido de fondo en esta situación de escucha.

The hearing aid occlusion effect: Measurement devices compared

Hearing aid users frequently complain about the sound quality of their own voices. One of the most common complaints, particularly among new users, is that their voice sounds “hollow” or as if they are “talking in a barrel.” Although such complaints sometimes result from suboptimal hearing aid settings, they also may be associated with significant occlusion created by the hearing aid shell or earmold.1-3 When a person vocalizes, the resulting bone-conducted energy causes vibration of the mandible and the soft tissue located close to the external canal. This causes vibration of the canal’s cartilaginous walls, producing energy that is subsequently transferred to the volume of air within the canal. When the ear canal is occluded, much of this energy is trapped, causing an increase in the sound pressure level delivered to the tympanic membrane and, ultimately, to the cochlea. For some closed vowels, occluding the external ear using a shallow insertion depth can result in levels of 100 dB SPL or more within the canal.4 This energy is centered primarily in the low frequencies, with the peak of the occlusion effect typically occurring in the range of 200 to 500 Hz.5 See Mueller et al.1 and Mueller8 for further discussion. Patient dissatisfaction resulting from the occlusion effect can lead to inconsistent hearing aid use or even rejection.4 The 2001 Knowles MarkeTrak VI report of trends in the hearing instrument market found that only 54% of surveyed hearing aid owners were satisfied with the sound quality of their own amplified voice.6 This was 4% below the satisfaction rate reported in the 1997 MarkeTrak V survey.7 One need only peruse the latest product information from hearing aid manufacturers to realize that occlusion reduction has become a highly marketed feature, although it is questionable that all these approaches are truly effective. As dispensers continue to fit smaller custom instruments that provide limited venting options and to fit patients with milder degrees of hearing loss, they can expect to continue fielding complaints resulting from the occlusion effect.8 The magnitude of the occlusion effect is highly variable among patients.5 Since this effect can decrease user satisfaction, it is critical that clinicians evaluate their patients’ own-voice complaints objectively and treat them systematically. This is because the dispenser must first determine if the source of the problem is the occlusion effect or if it is related to the gain settings of the hearing aid, which is an entirely different problem. If the problem is indeed the occlusion effect, then the dispenser must perform objective measures to monitor treatment—the effects of venting or adjustment of shell/earmold canal length. Traditionally, probe-microphone equipment has been used to measure the occlusion effect objectively. More recently, Etymotic Research introduced a hand-held device, the ER-33 occlusion effect meter. The primary purpose of this study was to compare the results of ER-33 measurements with those obtained with traditional probe-microphone equipment. In addition, we examined the effects of venting, since the current evidence on the effectiveness of this occlusion treatment is conflicting.

Clinical Verification of Hearing Aid Performance

The general goal of providing amplification is to improve functional auditory capacity and restore good communication skills. Amplification should restore the audibility of soft sounds, provide improved intelligibility of speech at conversational listening levels, and ensure that intense sounds are not amplified to an uncomfortably loud level. There are several prescription methods that provide frequency-specific target values for soft, conversational, and intense sounds. Despite differences in the target values, no validated prescription method has been clearly shown to be superior to any of the other methods in terms of patient benefit (e.g., greater satisfaction, less residual disability). However, clinical studies have clearly shown that when a well-researched prescriptive approach is used and appropriate gain is delivered across frequencies, speech intelligibility is enhanced, and there is improved patient benefit and satisfaction. There is also irrefutable evidence that the audiologist can improve the match to the prescription target values using a probe microphone placed within the patient’s ear canal. As a result, carefully conducted verification is an essential component of long-term success with amplification. The most recent generation of prescription methods provides a degree of personalization to the target values beyond that associated with hearing threshold levels. However, there is an urgent clinical need to address the wide range of clinical outcomes that occur in hearing aid users with apparently similar characteristics.

The Best of 2000: Hearing aids

O Journal Club is back for another year—but where have you gone, Sam and Denis? When most of you think back on 2000 you probably recall the strangest presidential election we’ve ever had or the year you lost 50% of your retirement funds in the stock market. But if your interest lies in hearing aids and hearing aid research, you probably remember 2000 as the year we lost two of the true giants of our field: Sam Lybarger and Denis Byrne. Most younger readers probably never met Sam Lybarger—-most of his accomplishments took place long before you were born. However, whatever your age, you’ve all benefited from his excellent publications on hearing aid design, earmold plumbing, and electroacoustic assessment. Although Sam was perhaps best known for his “1/2 gain rule,” developed in the 1940s, his accomplishments go far beyond hearing aid selection techniques. He chaired the ANSI standards hearing aid committee for over 30 years, and was instrumental in developing vacuum tube aids with crystal microphones, the inductive telephone pickup in wearable hearing aids, and the B70 and B71 bone vibrators. Sam also had a lighter side, evidenced by what is no doubt his most quoted sentence: “A hearing aid is an ultra-small electro-acoustic device that is always too large, that has to faithfully amplify The Best of 2000: Hearing aids