Digital Signal Processing Hearing Aids, Personal FM Systems, and Interference: Is There a Problem?

There is no doubt that the hearing healthcare profession is at the dawn of an exciting new era in the advancement of hearing aid technology. Within the last few years there has been a major shift from dispensing linear hearing aid technology into a new era of so many unique hearing aid circuit choices. Today there are so many choices, from improved and more sophisticated linear circuits, i.e., class D amplifiers, to almost completely adjustable nonlinear analog and most recently fully digital circuits! Keeping current with today's hearing aid technology challenges even the most dedicated hearing healthcare professional. In fact, the idea of keeping current is what best summarizes the primary focus of this manuscript. At Frye Electronics, we are continually striving to find better, easier and more helpful methods of evaluating the electroacoustic performance of a hearing aid. An example of this commitment is the experimental “digital speech” software approach for evaluating the performance of the new digital signal processing hearing aids that we demonstrated at this year's American Academy of Audiology convention. We believe that the new Frye/SPL fitting test will help dispensers keep up with today's new technology by providing hearing healthcare professionals with an important next step that is both a practical and easy-to-use fitting approach for utilization with all types of hearing aids.

Digital signal processing hearing aids: determining need on an individual basis.

The purpose of this paper was to provide audiologists practical information regarding the use of direct-input hearing aids with FM systems. The degree to which the electroacoustic characteristics of direct-input hearing aids were preserved when used with two different personal FM systems was evaluated. Although there were limited changes in saturation sound pressure level and harmonic distortion, there was an increase in equivalent-input noise and full-on-gain. The frequency response curve of the aid + FM condition relative to the aid alone differed in the high frequencies for the two FM systems. Aids with equivalent gain values had varying amounts of gain when tested with the FM systems set at a constant volume control setting. This variability in the electroacoustic response of a given aid when coupled to a personal FM system suggests that one may not assume characteristics of the hearing aid are maintained when it is used with an FM system.

Sensorineural hearing loss is associated with elevated hearing thresholds, reduced dynamic range, and loudness recruitment. Dynamic range compression in the hearing aids is provided for restoring normal loudness of low level sounds without making the high level sounds uncomfortably loud. A sliding-band compression is presented for significantly reducing the temporal and spectral distortions generally associated with the currently used single and multiband compression techniques. It uses a frequency-dependent gain function calculated on the basis of critical bandwidth based short-time power spectrum and the specified hearing thresholds, compression ratios, and attack and release times. It is realized using FFT-based analysis-synthesis and can be integrated with other FFT-based signal processing in hearing aids to save computation. The technique is implemented and tested for satisfactory real-time operation, with sampling frequency of 10 kHz, window length of 25.6 ms with 75% overlap on a 16-bit fixed-point DSP processor with on-chip FFT hardware.

To investigate the music perception skills of adult cochlear implant (CI) users in comparison with hearing aid (HA) users who have similar levels of hearing impairment. It was hypothesized that the HA users would perform better than the CI recipients on tests involving pitch, instrument, and melody perception, but similarly for rhythm perception. Fifteen users of the Nucleus CI system and 15 HA users participated in a series of music perception tests. All subjects were postlingually deafened adults, with the HA subjects being required to meet the current audiological criteria for CI candidacy. A music test battery was designed for the study incorporating four major tasks: (1) discrimination of 38 pairs of rhythms; (2) pitch ranking of one-octave, half-octave, and quarter-octave intervals; (3) instrument recognition incorporating three subtests, each with 12 different instruments or ensembles; and (4) recognition of 10 familiar melodies. Stimuli were presented via direct audio input at comfortable presentation levels. The test battery was administered to each subject on two separate occasions, approximately 4 mo apart. The results from the rhythm test were 93% correct for the CI group and 94% correct for the HA group; these scores were not significantly different. For the pitch test, there was a significant difference between the HA group and the CI group (p < 0.001), with higher mean scores recorded by the HA group for all three interval sizes. The CI subject group was unable to rank pitches a quarter-octave apart, only scoring at chance level for this interval size. In the instrument recognition test, although there was no significant difference between the mean scores of the two groups, both groups obtained significantly higher scores for the subtest incorporating single instrument stimuli than those incorporating multiple instrumentations (p < 0.001). In the melody test, there was a significant difference between the implantees' mean score of 52% correct and the HA group's mean of 91% (p < 0.001). As hypothesized, results from the two groups were almost identical for the rhythm test, with the HA group performing significantly better than the CI group on the pitch and melody tests. However, there was no difference between the groups in their ability to identify musical instruments or ensembles. The results of this study indicate that HA users with similar levels of hearing loss perform at least equal to, if not better than, CI users on these music perception tests. However, despite the differences between scores obtained by the CI and HA subject groups, both these subject groups were largely unable to achieve accurate or effective music perception, regardless of the device they used.

FigureThere is a different type of hearing device called the Baha® bone conduction implant, also known as an osseointegrated auditory prosthesis, that is made especially for people with a long history of sick ears and ear surgeries. Such patients tend to be frustrated with their poor hearing and are often nervous about the risk of another ear infection. They also want to avoid more ear surgery at all costs. If the health of the ear can be stabilized, which is often a challenge, a conventional hearing aid may be used. Unfortunately, ear infections tend to recur, making regular hearing aids contraindicated for long periods of time. Years ago we fitted people who had this problem with a bone conductor on a headband attached to a high-power, body-worn hearing aid. Some of these fittings brought much happiness to patients who after not hearing sound for many years suddenly could hear well. The down side of this type of fitting is the wear and tear that the vibrator and the headband inflict on the wearer's head. The band is often too loose or too tight. It is hard to keep in place, and it is uncomfortable to wear. Extended use of the vibrator leads to an indentation in the patient's head created by the constant pressure exerted by the bone vibrator, which eventually erodes the bone directly under the vibrator. We usually try to fix this problem by moving the vibrator to the opposite side of the head, but eventually patients move it back to the original spot because it allows them to hear better. Developed in Sweden in 1977, Baha received FDA clearance for use in this country in 1996. Cochlear purchased Entific, the company that made it, in 2005. HOW IT WORKS Implanting the Baha is a relatively simple surgical procedure. A prosthesis is screwed into the mastoid. Then, 3 to 6 months later, the Baha sound processor is attached to the prosthesis with a coupler. For people who have good hearing via bone conduction and poor hearing via air conduction, this can work extremely well. The amplified sound bypasses the defective outer and middle ear and goes directly into both inner ears. The quality of hearing is described as quite good. Currently, Baha implantation is restricted to people age 5 years and above. Before that age, a child may use a Baha sound processor worn on a soft band and used similarly to a conventional bone-conduction hearing aid. After surgery, the child may use the same Baha sound processor on the implant and abutment. The reason for restricting implantation by age is that younger children are thought to have immature bone density, which may not permit good osseointegration. To ensure osseointegration with pediatric patients, it is recommended that the sound processor not be attached to the prosthesis until 6 months after surgery. In adults the waiting period is usually 3 months. Figure 1 shows the parts of the Baha. The separate piece in the photo is the small titanium implant that is screwed into the bone behind the patient's ear. New bone tissue grows around the implant securing it to the head. The implant is attached to an abutment that connects it to the hearing aid. The main part of the system is the sound processor, which receives the sound, amplifies it, and then transfers it to the patient via vibrations.Figure 1: The Baha system.ADVANTAGES For appropriate candidates, Baha has several benefits over alternative fittings: Feedback is reduced or eliminated. There is no discomfort from wearing a large, tightly fitting earmold. The conductive hearing loss is bypassed so the power requirement is lower. Reducing the required gain results in less saturation and distortion. There is no headband to wear. Because Baha is perceived as a surgical procedure rather than a hearing aid, it is currently approved by Medicare and many insurance companies. ACCESSORIES Various accessories can be used with Baha. Direct audio input is available so the patient can connect to a stereo, TV, or MP3 player. The unit can be used with a Microlink FM receiver to help with classroom situations and hearing in noise. A telecoil unit can be used to improve telephone listening. SUMMARY If conventional hearing aids or ear surgery does not provide a patient with good hearing, then a Baha should be considered. Its use is indicated when feedback is intractable and/or when the patient suffers from irritated ears or has malformed ears or ear canals. The Baha is also sometimes recommended for single-sided deafness.

Binaural speech intelligibility in rooms is a complex process that is affected by many factors including room acoustics, hearing loss, and hearing aid (HA) signal processing. Intelligibility is evaluated in this paper for a simulated room combined with a simulated hearing aid. The test conditions comprise three spatial configurations of the speech and noise sources, simulated anechoic and concert hall acoustics, three amounts of multitalker babble interference, the hearing status of the listeners, and three degrees of simulated HA processing provided to compensate for the noise and/or hearing loss. The impact of these factors and their interactions is considered for normal-hearing (NH) and hearing-impaired (HI) listeners for sentence stimuli. Both listener groups showed a significant reduction in intelligibility as the signal-to-noise ratio (SNR) decreased, and showed a reduction in intelligibility in reverberation when compared to anechoic listening. There was no significant improvement in intelligibility for the NH group for the noise suppression algorithm used here, and no significant improvement in intelligibility for the HI group for more advanced HA processing algorithms as opposed to linear amplification in either of the two acoustic spaces or at any of the three SNRs.

&lt;p&gt;&lt;b&gt;Speech enhancement was, is, and will be the key technology for digital speech transmission. When developing speech enhancement algorithms, the intelligibility or the quality of the processed speech needs to be evaluated. Intelligibility is more fundamental than quality. The evaluation of speech intelligibility can be carried out through subjective listening tests and objective metrics. Carrying out subjective listening tests is time-consuming and costly. Using the objective metrics is more efficient. Thus, there has been an increasing research in speech intelligibility prediction.&lt;/b&gt;&lt;/p&gt; &lt;p&gt; Speech intelligibility can be measured in terms of the information received by a listener. This thesis aims at developing a mutual information-based speech intelligibility predictor (SIP) and using the mutual information-based predictor to assist the fitting process in hearing instruments. To achieve this goal, this thesis carried out three studies. &lt;/p&gt; &lt;p&gt;First, it studied the modeling of the transmitted message. For mutual information-based SIPs, the most important thing is to determine the transmitted message. This thesis studied two approaches of modeling of the message: one is the continuous-valued sound, and the other is the discrete-valued linguistic message. Two corresponding SIPs were developed. By comparing their predicted intelligibility results with the psychometric curves, which are the subjective intelligibility scores, it shows that the modeling of discrete-valued message gives a better match to the psychometric curves.&lt;/p&gt; &lt;p&gt; Second, based on the modeling of the discrete-valued message, this thesis proposed a mutual information-based SIP. Since the discrete-valued message cannot be obtained from a speech signal, the proposed SIP calculates the mutual information between the clean speech and the received speech, instead of calculating the mutual information between the message and the received speech. The proposed SIP considers frequency correlation for both the clean speech and the received speech. The evaluation results show that the proposed SIP performs better than the existing state-of-the-art mutual information-based SIPs.&lt;/p&gt; &lt;p&gt;Third, this thesis proposed an automatic fitting tool for the nonlinear frequency compression (NFC) operator, which is a frequency lowering operator used in hearing instruments. The automatic fitting tool adjusts the parameter in the NFC by maximizing the mutual information between the message and the frequency-lowered speech. To evaluate the automatic fitting tool, the parameter was also searched by listening tests. The results show that the parameter determined by the automatic fitting tool is consistent to the parameter determined by the listening tests.&lt;/p&gt;

Intervention for a Child with Auditory Neuropathy/Dys-synchrony

The purpose of this article is to discuss 2 questions concerning how hearing aids interact with hearing and cognition: Can signal processing in hearing aids improve memory? Can attention be used for top-down control of hearing aids? Memory recall of sentences, presented at 95% correct speech recognition, was assessed with and without binary mask noise reduction. A short literature review was performed on recent findings on new brain-imaging techniques showing potential for hearing aid control. Two experiments indicate that it is possible to show improved memory with an experimental noise reduction algorithm at ecological signal-to-noise ratios and that it is possible to replicate these findings in a new language. The literature indicates that attention-controlled hearing aids may be developed in the future.

You have accessThe ASHA LeaderFeature1 Nov 2011Improving Hearing Aid Function in Noisy Situations Tamara StenderAuD, CCC-A Tamara Stender Google Scholar More articles by this author , AuD, CCC-A https://doi.org/10.1044/leader.FTR5.16132011.5 SectionsAbout ToolsAdd to favorites ShareFacebookTwitterLinked In http://www.asha.org/Publications/leader/2011/111101/Improving-Hearing-Aid-Function-in-Noisy-Situations.htm Even with today’s sophisticated hearing aid advances in microphone directionality and noise-reduction circuitry (Chung, 2010), hearing-instrument users still experience difficulties in some challenging environments, such as in restaurants and at parties. Almost half of hearing-aid users who return their devices cite problems with hearing over background noise (Kochkin, 2007). It is no surprise that use in noisy situations is listed as one of the top 10 factors pertaining to hearing aid user dissatisfaction (Kochkin, 2010). Innovative approaches to facilitating hearing in noise, therefore, may further increase hearing- instrument users’ satisfaction. These approaches include strategic microphone placement in non- directional devices and the use of wireless accessories that stream the speaker’s voice directly to the listener’s hearing aids. Microphone Placement Strategic microphone placement taps the natural physical characteristics of the external ear to improve speech intelligibility. Outer ear structures have been shown to contribute to greater directivity toward the front than the rear (Ricketts, 2000; Shaw, 1974), which may translate to better speech understanding in noise in situations where the listener is facing the speaker. Conversely, when the microphone of a hearing instrument is positioned behind the ear, all pinna effects—including the ear’s natural directivity and protection from wind noise—are obliterated. However, moving the microphone inside the ear canal or even within the bowl of the concha maintains some of these favorable pinna effects, thereby naturally restoring some of the ear’s physiological ability to help the listener discriminate speech from noise. A relatively new hearing aid model on the market takes advantage of natural pinna effects ( Figure 1 [PDF], left panel). This form factor is similar to a conventional custom in-the-canal (ITC) device (right panel), except the microphone is removed from the shell and extends into the upper part of the concha. Removal of the microphone from the shell may allow for a smaller device or a larger vent. Yet since the microphone is still secured within the ear, natural directivity and spectral cues provided by the pinna are maintained (Van den Bogaert, Carette, & Wouters, 2011). A study at Walter Reed Army Medical Center revealed no significant difference in hearing-in-noise test results between this new custom form factor and a directional behind-the-ear hearing instrument (Cord & Block, 2011). In addition, the natural protection afforded by locating the microphone in the crevices of the outer ear (the concha) reduces the intensity of wind noise. Figure 2 [PDF] shows a spectrogram of wind noise measured in a hearing instrument with the microphone located within the concha (left panel) and with the microphone behind the ear (right panel). Red areas indicate the areas of highest energy across the frequency range due to wind noise. Accessories Another approach to improving speech in noise is the use of wireless accessories to stream the speaker’s voice directly to the hearing instruments. One of these approaches is a wireless hearing aid accessory that communicates through Bluetooth technology to the mobile phone (or Bluetooth-enabled landline phone). Bluetooth is an open technology that uses radio frequencies in the 2.4-GHz range to send data wirelessly over a limited distance. After pairing the accessory to the Bluetooth-ready phone and the hearing aids, the user is able to conduct phone conversations at a more favorable signal-to-noise ratio than without the accessory. In addition, the conversation is streamed simultaneously to both hearing aids, providing the additional benefit of binaural listening adjusted to the user’s hearing thresholds for each ear. Another wireless accessory is a personal wireless microphone that speakers can clip onto their clothing. Akin to a separate FM system that uses a transmitter and a receiver or boots that attach to the hearing instrument(s), this technology effectively improves the signal-to-noise ratio for the listener, especially in an environment with background noise. New direct wireless transmission, however, requires no additional boots or receivers for the listener. This technological advancement means reduced cost and hassle for the hearing-instrument user. Additional methods of promoting speech intelligibility in noise—in addition to hearing aid algorithms—may be necessary to reduce the return rate and the number of hearing aids stored in the drawer. With strategic microphone placement, which allows for natural directivity and wind noise protection in non-directional hearing instruments, and wireless technology that directly streams a more favorable signal-to-noise ratio, hearing in noise may become easier for hearing-instrument users. References Bluetooth. (2011, June 20). InWikipedia, The Free Encyclopedia.Retrieved 15:41, June 21, 2011, fromhttp://en.wikipedia.org/w/index.php?title=Bluetooth&oldid=435265724. Google Scholar Chung K. (2010). Reducing noise interference: Strategies to enhance hearing aid performance.The ASHA Leader, 15(4), 10–13. Google Scholar Cord M., & Block K. (2011, March). Efficacy of the remote microphone hearing aid for novice hearing aid users.Presented at Joint Defense Veteran Audiology Conference (JDVAC), San Diego, CA. Google Scholar Hearing Industries Association (HIA) (2010). Statistical reporting program.Washington, DC. Google Scholar Kochkin S. (2010). MarkeTrak VIII: Customer satisfaction with hearing aids is slowly increasing.Hearing Journal, 63(1), 11–19. Google Scholar Kochkin S. (2007). MarkeTrak VII: Obstacles to adult non-user adoption of hearing aids.Hearing Journal, 60(4), 27–43. Google Scholar Nilsson M., Soli S. D., & Sullivan J. A. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise.Journal of the Acoustical Society of America, 95(2), 1085–1099. CrossrefGoogle Scholar Ricketts T. (2000). Directivity quantification in hearing aids: fitting and measurements effects.Ear & Hearing, 21(1), 45–58. Google Scholar Shaw E. A. G. (1974). Transformation of sound pressure level from the free field to the eardrum in the horizontal plane.Journal of the Acoustical Society of America, 56(6), 1848–1861. Google Scholar Van den Bogaert T., Carette E., & Wouters J. (2011). Sound source localization using hearing aids with microphones placed behind-the-ear, in-the-canal, and in-the-pinna.International Journal of Audiology, 50(3), 164–176. Google Scholar Author Notes is a senior audiologist in Global Audiology for GN ReSound Group. Her research interests include hearing aid benefit and satisfaction, and the use of signal processing and other methods to improve speech discrimination in noise. Contact her at[email protected]. 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Three different non-linear digital signal processing algorithms were developed; LinEar, DynEar and RangeEar. All three provided individual frequency shaping via a seven-band low-power filterbank and compression in two channels. RangeEar and DynEar used wide dynamic range syllabic compression in the low-frequency (LF) channel, while LinEar used compression limiting. In the high-frequency (HF) channel, RangeEar used a slow-acting automatic volume control, while DynEar and LinEar used compression limiting. Wearable digital signal processing-based experimental instruments were used to evaluate the fitting algorithms under real world conditions with experienced hearing aid users. Evaluation included laboratory testing of speech recognition in noise and questionnaires on sound quality ratings. Results did not indicate one general good-for-all algorithm, but different algorithms resulting in preference and performance depending on the hearing loss configuration. Preference for any of the new algorithms could be predicted based on auditory dynamic range measurements. It was hypothesized that the different preferences were affected by different susceptibility to masking of HF sounds by amplified LF sounds.

This study investigated (a) the effect of amplification on cortical auditory evoked potentials (CAEPs) at different signal levels when signal-to-noise ratios (SNRs) were equated between unaided and aided conditions, and (b) the effect of absolute signal level on aided CAEPs when SNR was held constant. CAEPs were recorded from 13 young adults with normal hearing. A 1000-Hz pure tone was presented in unaided and aided conditions with a linear analog hearing aid. Direct audio input was used, allowing recorded hearing aid noise floor to be added to unaided conditions to equate SNRs between conditions. An additional stimulus was created through scaling the noise floor to study the effect of signal level. Amplification resulted in delayed N1 and P2 peak latencies relative to the unaided condition. An effect of absolute signal level (when SNR was constant) was present for aided CAEP area measures, such that larger area measures were found at higher levels. Results of this study further demonstrate that factors in addition to SNR must also be considered before CAEPs can be used to clinically to measure aided thresholds.

The objective of this investigation was to compare real and perceived benefit for two currently marketed digital hearing aids, the Oticon DigiFocus and the Widex Senso. The hearing aids have different philosophies of design and fitting strategies; as a result, it was hypothesized that there would be performance differences. Twenty subjects with documented sensorineural hearing losses were fit with each of the two digital hearing aids. After 4 wk of use with each hearing aid, a battery of objective and subjective tests was completed to assess hearing aid benefit. No significant differences were found between the hearing aids as revealed by the objective testing of speech recognition and self-report inventories of hearing aid benefit. The DigiFocus was shown by real ear measurements to provide more high-frequency gain than the Senso. The Widex Senso was preferred by 13 of the 20 subjects (seven of 10 of the new hearing aid users). This may be explained, in part, by the increased high-frequency gain provided by the Oticon DigiFocus, which was perceived as having greater "harshness." Based on the results of this investigation, neither hearing aid processor was shown to be superior to the other. In addition, the least amount of objective benefit was shown in the presence of background noise.

The purpose of this study was to investigate problems relating to phonation and self-perceived voice sound quality in older adults based on hearing ability and the use of hearing aids. This was a cross-sectional study, with 290 participants divided into 3 groups (matched by age and gender): (a) individuals with hearing impairments who did not use hearing aids (n = 110), (b) individuals with hearing impairments who did use hearing aids (n = 110), and (c) individuals with no hearing impairments (n = 70). All participants underwent a pure-tone audiometry exam; completed standardized questionnaires regarding their hearing, voice, and general health; and were recorded speaking in a soundproof room. The hearing aid users surpassed the benchmarks for having a voice disorder on the Voice Handicap Index (VHI; Jacobson et al., 1997) at almost double the rate predicted by the Swedish normative values for their age range, although there was no significant difference in acoustical measures between any of the groups. Both groups with hearing impairments scored significantly higher on the VHI than the control group, indicating more impairment. It remains inconclusive how much hearing loss versus hearing aids separately contribute to the difference in voice problems. The total scores on the Hearing Handicap Inventory for the Elderly (Ventry & Weinstein, 1982), in combination with the variables gender and age, explained 21.9% of the variance on the VHI. Perceiving one's own voice as being distorted, dull, or hollow had a strong negative association with a general satisfaction about the sound quality of one's own voice. In addition, groupwise differences in own-voice descriptions suggest that a negative perception of one's voice could be influenced by alterations caused by hearing aid processing. The results indicate that hearing impairments and hearing aids affect several aspects of vocal satisfaction in older adults. A greater understanding of how hearing impairments and hearing aids relate to voice problems may contribute to better voice and hearing care.