New tricks allow hearing aids to cope better with high frequencies, making speech and music more comprehensible

Music to the ear

Medical technology: New tricks allow hearing aids to cope better with high frequencies, making speech and music more comprehensible

Mar 9th 2013 |From the print edition

THE human voice, like any sound produced by thrumming a stretched string, has a fundamental frequency. For voice, the centre of that frequency lies mostly below 300Hz depending on the speaker’s sex and the sounds in question. Information is conveyed through simultaneous higher-frequency overtones and additional components that can stretch up to 20,000Hz (20kHz). Modern hearing aids are able to distinguish only a small part of that range, typically between 300Hz and 6kHz, reducing noise and amplifying those frequencies where the wearer’s hearing is weakest.

But differentiating elements of many common parts of speech occur in higher frequencies. This is the result both of harmonics that ripple out from the main tone, and from non-voiced elements used to utter consonants, which employ the tongue, teeth, cheeks and lips. Take the words “sailing” and “failing”. Cut off the higher frequencies and the two are indistinguishable. The problem is compounded on telephone calls, which do not transmit frequencies below 300Hz or above 3.3kHz, resulting in the need for cues like “S for Sierra, F for Foxtrot”.

People with hearing aids experience this problem constantly, says Brian Moore of the University of Cambridge. Typical hearing loss tends to be most acute at frequencies above 10kHz, which contain quieter sounds but where speech can still include important cues (as well as progressively less important ones extending up to 20kHz). Older hearing aids cut off at no higher than 6kHz, but much modern equipment stretches this range to 8-10kHz. However, a problem remains, Dr Moore says, because bespoke hearing-aid calibrations for individual users, called “fittings”, do not properly boost the gain of these higher frequencies. So Dr Moore and his colleagues have come up with a better method. Their approach can be applied to many existing devices, and is also being built into some newer ones.

A key step in any fitting involves testing an individual’s ability to hear sounds in different frequency bands. Each hearing loss is unique, and for most users a standard profile would be too loud in some ranges and too soft in others. But current tests pay scant attention to the higher frequencies that a device’s tiny speaker can produce, regardless of whether the user needs a boost. Dr Moore’s new test, known as CAM2, which is both a set of specifications and an implementation in software, extends and modifies fittings to include frequencies as high as 10kHz. When the results are used to calibrate a modern hearing aid, the result is greater intelligibility of speech compared with existing alternatives. CAM2 also improves the experience of listening to music, which makes greater use of higher frequencies than speech does.

The university’s licensing arm has been busy plugging Dr Moore’s software and found an early taker in EarLens, a Californian maker of a device with a 10kHz range. EarLens’s gizmo comprises two parts: a behind-the-ear microphone and a vibrating actuator that has direct contact with the eardrum. An infra-red beam focused into the ear carries the signal from the removable external component to the actuator. (The company has yet to secure regulatory approval for its device and is therefore cagey about revealing the technical details.)

Another firm, called Sonitus, has developed an alternative approach to extend the frequency range to 12kHz. Its SoundBite aid, which has been approved for sale in America, uses an in-ear microphone coupled with a behind-the-ear transmitter that sends audio wirelessly to a removable receiver inside the mouth. The receiver is custom-fitted to a user’s teeth, and takes advantage of bone conductivity to bypass the inner ear and stimulate the cochlea directly. It is designed as an alternative to bone-anchored hearing aids. These are nifty, but deliver a relatively narrow frequency range.

Crucially, bone-anchored devices require surgery to implant a screw at the base of the skull onto which a customer snaps a removable, battery-powered microphone and vibrator. The SoundBite does away with the need for such invasive procedures, making it cheaper and safer, as well as more versatile, while the EarLens requires only the relatively straightforward placement of the eardrum actuator. The hard of hearing will love the sound of that.

About bambooinnovator
Kee Koon Boon (“KB”) is the co-founder and director of HERO Investment Management which provides specialized fund management and investment advisory services to the ARCHEA Asia HERO Innovators Fund (www.heroinnovator.com), the only Asian SMID-cap tech-focused fund in the industry. KB is an internationally featured investor rooted in the principles of value investing for over a decade as a fund manager and analyst in the Asian capital markets who started his career at a boutique hedge fund in Singapore where he was with the firm since 2002 and was also part of the core investment committee in significantly outperforming the index in the 10-year-plus-old flagship Asian fund. He was also the portfolio manager for Asia-Pacific equities at Korea’s largest mutual fund company. Prior to setting up the H.E.R.O. Innovators Fund, KB was the Chief Investment Officer & CEO of a Singapore Registered Fund Management Company (RFMC) where he is responsible for listed Asian equity investments. KB had taught accounting at the Singapore Management University (SMU) as a faculty member and also pioneered the 15-week course on Accounting Fraud in Asia as an official module at SMU. KB remains grateful and honored to be invited by Singapore’s financial regulator Monetary Authority of Singapore (MAS) to present to their top management team about implementing a world’s first fact-based forward-looking fraud detection framework to bring about benefits for the capital markets in Singapore and for the public and investment community. KB also served the community in sharing his insights in writing articles about value investing and corporate governance in the media that include Business Times, Straits Times, Jakarta Post, Manual of Ideas, Investopedia, TedXWallStreet. He had also presented in top investment, banking and finance conferences in America, Italy, Sydney, Cape Town, HK, China. He has trained CEOs, entrepreneurs, CFOs, management executives in business strategy & business model innovation in Singapore, HK and China.

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