Hearing Aid Technology for the 21st Century

Hearing Aid Technology for the 21st Century

A proposal for universal wireless connectivity and improved sound quality.

Approximately 360 million people in the world live with a debilitating hearing loss. The most common conditions—age-related and noise-induced sensorineural hearing loss—are both progressive and, for the foreseeable future, neither curable nor reversible.

Because they find it difficult, if not impossible, to un – derstand what others are saying, people with serious hearing loss find themselves increasingly isolated from family, friends, and coworkers. They can’t attend business meetings, enjoy a dinner table conversation, go to the movies, or even hear their grandchildren laugh. In addition to the devastating social and psychological isolation, hearing loss is linked to increased economic hardship, cognitive issues, and other serious problems [1], [2].

While hearing aids are the most common devices used to compensate for the majority of hearing losses, they are widely available only in the most highly developed countries. Even in the United States, only 16% of adults 20–69 and 30% of adults over 70 who could benefit from hearing aids actually use them, and the adoption rate for hearing aids has grown slowly despite extraordinary technological advances in the field.

While there are many reasons for their underuse, including high cost and stigma, I believe one major reason is that hearing aids simply do not work very well in many noisy environments where they are needed the most. From the standpoint of engineering and design, the performance of hearing aids can be dramatically improved with advanced universal wireless audio interconnectivity and better overall sound quality.

Hearing in the 21st Century

To be sure, modern digital hearing aids are marvels of sophisticated engineering and miniaturization. Indeed, those of us who wear hearing aids are very grateful to have them. A typical behind-the-ear device is quite small (roughly 3-cm long) yet still includes an array of two or more microphones, digital audio converters, programmable digital signal processing (DSP) that delivers complex compression algorithms as well as advanced feedback suppression, a telecoil for both phone and induction loop coupling, and amplifiers. All of this capability (and much more) runs for up to four days on a battery half the size of a pinky fingernail.

However, typical sensorineural hearing loss cannot be corrected the way, for example, that most vision problems can. Even the most advanced digital technology can only partially compensate for the numerous complex and often extreme distortions of volume, frequency response, clarity, and aural resolution that hearing loss creates

Modern hearing aids can often be effective in relatively quiet environments. In noisy environments, their basic design, which trades off effective acoustical performance in the presence of noise for near invisibility, often provides less than adequate performance. One major reason: a hearing aid’s microphones—positioned at the listener’s ears, which are typically at least a meter‘ s distance from the sound source—are too far away to pick up clear sound in common real-world environments. In many restaurants, for example, neither directional microphones nor any practical real-time DSP can compensate for suboptimal microphone placement, especially given that people with hearing loss require a much higher than normal signal-to-noise ratio (SNR) for adequate speech recognition.

The ideal place to position a microphone for good speech pickup is as close as possible to the person speaking. With a remote microphone providing a relatively clean signal, any DSP now available can do a better job, and less is usually necessary. Hearing aid manufacturers do offer wireless remote microphones; however, they are expensive, sometimes hard to use, proprietary, and often require additional electronic devices that are unfamiliar looking and unattractive.

As a result, remote microphones and similar devices are not widely used by people who could benefit from them. If they could be paired with any brand of hearing aids or if the microphone on a smartphone could be configured as a wireless remote, more people would likely avail themselves of the improved sound. But current attempts to do this are very unreliable and of poor quality.

The difficulty of connecting remote microphones points to a much larger issue in current hearing aid design: poor interconnectivity with amplified sound. A huge percentage of our spoken communications today takes place via electronic audio devices such as telephones, remote business conference technologies, TV speakers, and movie theater sound systems. To be a functioning citizen in the 21st century—to work effectively, to be a student, to travel, to enjoy modern performing arts and entertainment, even to attend a worship service—it is essential to hear amplified sound clearly. Without the ability to access amplified sound, it is impossible for nearly everyone in the developed world to stay connected.

Although many people with hearing loss can, in fact, understand speech quite well when amplified sound is delivered directly to their aids, there is no easy way to reliably connect hearing aids to most modern sound technologies. And even to try to stay connected, a person with hearing loss has to navigate a daunting array of mutually incompatible, proprietary, and very finicky wireless technologies, including FM, infrared, induction loops, and Bluetooth. Moreover, he or she would have to be prepared to swap out hearing aids for wired earphones several times a day. Even then, much electronic audio—for example, public address (PA) announcements in airports—would remain completely inaccessible.

Advanced Universal Wireless Audio Connectivity

To hear modern audio, a nonproprietary, low-latency, highly flexible wireless solution is needed that would enable in-ear hearing devices to connect seamlessly with the wide variety of audio signals people encounter every day. To the user, it should look as though the same technology that connects his or her hearing aid to a smartphone can also enable direct audio connection to other audio sources, from televisions to PA systems to conferencing technology to personal remote microphones.

Better wireless connectivity is partly dependent on larger batteries for hearing aids, and larger batteries mean larger, visible devices. While there is a lot of stigma associated with wearing hearing assistance (even today, when so many people wear headphones in public), it’s possible that visibility would not be so important if hearing devices were truly effective and people could reliably hear loved ones and coworkers. It’s also quite possible that an advanced wireless connectivity solution would benefit normal-hearing listeners in classrooms, train stations, noisy restaurants, cars, conference calls, virtual reality setups, and wherever acoustics are poor.

The wide adoption of an open, low-latency, wireless connectivity solution for audio would require cooperation by companies that have historically believed profits are best optimized through the development of proprietary devices. But theirs is a short-sighted attitude. For example, imagine if a Google, Apple, or Microsoft device allowed you to connect online only to the company’s own services and made it impossible to connect to a competitor’s. We’d have three incompatible Internets! Similarly, an open wireless audio solution would likely see expanded use of currently popular—and even hitherto unimagined—technologies far beyond the hearing loss market.

While there is some interest in a common solution with advanced capabilities, Apple’s announcement of the new W1 chip for proprietary connectivity to the company’s AirPods suggests that the road to a universal wireless standard will not be straightforward. Yet, for consumers to adopt wireless en masse, connectivity needs to be as simple as possible. Although AirPods are intended to connect easily to Apple devices, they will likely provide comparatively poorer performance (such as higher latency and more complicated pairing) when connected to a competitor’s devices over Bluetooth.

From the standpoint of the normal-hearing user, this two-tiered performance arguably may be acceptable because users expect a premium experience if they commit to a specific manufacturer’s product line. However, in hearing health technology, significantly inconsistent performance across devices is a recipe for confusion and nonadoption. Many people with hearing loss are not at all familiar with consumer audio technology. Accordingly, two-tiered wireless performance capability will likely be perceived as an unreliable product, one that is simply unacceptable for technology that users must rely on to live their lives.

Initiatives to Promote Universally Compatible Wireless Connectivity

Many observers and stakeholders believe that universally compatible wireless connectivity is crucial for any significant improvement to hearing health technology. Furthermore, an advanced low-latency wireless solution would have numerous applications beyond hearing loss, such as in education, virtual reality, gaming, business conferencing, military deployment, sound reinforcement, and entertainment—in short, nearly all areas where audio technology is used.

To explore the issue and to identify ways to highlight the importance of universally compatible wireless connectivity, I helped organize a workshop held on 20 June 2016 at the Simons Foundation, a prominent scientific research institution based in New York City. Among those attending were hearing aid designers, a representative from the Consumer Technology Association, major designers of high-end professional audio equipment, prominent academics, and two board members of the Hearing Loss Association of America (including myself). The importance of the event was highlighted by the presence of several distinguished members of the Simons Foundation including Gerald Fischbach, Leslie Greengard, and founder James Simons himself. We agreed that a low-latency wireless audio solution is desirable and possible and should be offered as an option by manufacturers in future consumer audio devices.

We also agreed that additional meetings, workshops, and conferences would be helpful in bringing attention to the issue. A dedicated IEEE Pulse event would be an ideal forum to discuss the matter and demonstrate that a universal wireless solution leading to the adoption of sophisticated wireless hearing devices could make an enormous improvement in the lives of millions of people around the world with hearing loss.

Improved Sound Quality

In addition to inadequate performance in noise and limited interconnectivity, I believe that sound quality has also hampered the adoption of hearing aids. Viewed simply as audio devices, hearing aids, which can easily cost more than US$2,500 each, deliver sound quality that is much lower than consumer devices costing an order of magnitude less. For example, reported total harmonic distortion (THD) for hearing aids is typically between 2 and 3%, if not higher. By comparison, a representative pair of consumer earphones claims THD of < 0.05% at 1 kHz, far lower than any hearing aid.

Furthermore, hearing aids, to optimize speech perception, have very poor bass response. Response at 250 Hz is down about 30 dB from that at 3.5 kHz. Moderately priced consumer earphones have lower than 10-dB variation in frequency response over a similar range. In addition, the frequency range is limited to about 100 Hz–8 kHz, which, combined with speech algorithms that often create audible artifacts with musical content, makes hearing aids not very suitable for music.

Also, until quite recently, the input gain structure before the analog-to-digital converter of all major digital hearing aids clipped any signal higher than about 85-dB SPL. Many sounds in the real world exceed this level. The clipping is very unpleasant and fatiguing and reduces speech comprehension in the presence of noise. Only about two years ago did one of the major companies fix the problem [3], and others have since followed suit. However, all current aids that I’ve tried still do not provide a quality music experience, and not just for audiophiles. I have conducted many informal listening tests, and, more often than not, hearing aid users report they enjoy music more via consumer audio gear and possibly have improved speech comprehension.

Also, until quite recently, the input gain structure before the analog-to-digital converter of all major digital hearing aids clipped any signal higher than about 85-dB SPL. Many sounds in the real world exceed this level. The clipping is very unpleasant and fatiguing and reduces speech comprehension in the presence of noise. Only about two years ago did one of the major companies fix the problem [3], and others have since followed suit. However, all current aids that I’ve tried still do not provide a quality music experience, and not just for audiophiles. I have conducted many informal listening tests, and, more often than not, hearing aid users report they enjoy music more via consumer audio gear and possibly have improved speech comprehension.

While there is an increasing awareness that a different approach is needed for music perception and that improved music perception might have positive implications for speech perception as well, there is much to be done. A music lover with hearing loss such as myself can best enjoy a live concert of, say, chamber music by removing his or her hearing aids and using a smartphone rig consisting of a high-quality directional microphone attachment, an amplification app, and good earphones.

While the in-ear microphone placement in hearing aids does create potential feedback issues that a smartphone solution does not have, they are not insurmountable. True high-fidelity hearing aids are entirely possible. And, of course, if the latency in a wireless audio solution is low enough, there is no reason a smartphone could not be enlisted to provide an improved SNR and even better sound for live music.

Hear, Hear

Modern digital hearing aids, while vastly improved compared to the technology available only 20 years ago, are underused. A somewhat different design approach based on the adoption of a common, low-latency wireless audio solution, better microphone placement, and higher sound quality will dramatically improve performance and likely lead to wider use by people with hearing problems. Leaders from the hearing health, professional audio, and consumer electronics industries should agree to the adoption of a universal, low-latency wireless audio solution that will make it simple to connect all audio technology to in-ear hearing devices, such as hearing aids.

With these changes and improvements to the current hearing health model, millions of people who can barely function now would be able to hear significantly better, reconnect to their world, and thrive.

Additional Materials

There are several audio files to accompany this article.

Examples of what an air conditioner and a noisy restaurant sound like to a normal-hearing person versus a person with a hearing loss.

 

A very accurate simulation of what speech sounds like in my right ear after I experienced sudden hearing loss in June 2010 (I created this example using electronic music technology, comparing the sound in my highly damaged right ear to the sound in my left, which has a different kind of hearing loss but has no pitch/loudness problems.)

 

An example that demonstrates volume loss of –25 dB, which is considered a mild hearing loss; –40 dB, which is considered moderate; and −56, which is considered moderate–severe. (It is likely that you will still hear speech after the first drop in level; however, after the –40 dB drop, most listeners have considerable trouble understanding any speech, and the –56 dB drop is essentially inaudible.)

 

References

  1. D. G. Blazer, S. Domnitz, and C. T. Liverman, “Hearing health care for adults: Priorities for improving access and affordability,” National Academy Press, Washington, DC, pp. 51–63, 2016.
  2. B. C. J. Moore, Cochlear Hearing Loss: Physiological, Psychological and Technical Issues, 2nd ed. Hoboken, NJ: Wiley, 2007.
  3. L. Baekgaard, N. O. Knudsen, T. Arshad, and H. P. Andersen. (2013, Mar. 6). Designing hearing aid technology to support benefits in demanding situations, part 1. Hearing Review. [Online].

  • John Don Carlos

    Exactly right, technology can do much better! My hearing aids are terrible for music, I take them out and use headphones. They produce adequately loud but difficult to understand speech. I have used a remote lapel mic to bluetooth transmitter on the belt to bluetooth receiver around the neck to hearing aid – awkward – intrusive – unreliable – barely better than just giving on hearing. Excellent opportunity for IEEE to take the lead with research and standards.