Standards help the hard of hearing

By Julia King

Hearing aids: stigma or saviour? Many of us have watched elderly friends or relatives struggling to adjust the devices inside or behind their ears. Their gnarled and knotted fingers aren't as agile as when they were young, and the increasingly small devices are both difficult to access and impossible to see..

Hearing aids: facilitating communication

Fiddling with hearing aids often serves only to make them squeak as feedback sets in. Their wearers may be unable to hear the noise, but it causes annoyance to those in the vicinity with better hearing. That's a pretty bleak picture for old age – and also for those whose deafness, caused by disease or other factors, forces them to wear hearing aids.

Frustrating though they may be for users and those around them, imagine what it would be like to know that people are trying to communicate with you, because you can see their mouths moving, but to have no idea what they are saying.

You can recreate this world by putting cotton wool into your ears. All sounds are immediately muffled. Hearing aids help to prolong the period during which normal human communication is possible.

Not all people suffer equally. There are different types of hearing problems. Some have overall hearing loss and it is difficult to make sense of indistinct words. Others are missing various frequencies so only certain sounds are distorted. Those who suffer from tinnitus are subjected to a world of strange noises with intermittent or continuous streams of ringing, buzzing, humming or whistling. In this case a hearing aid may not relieve their symptoms altogether although it might help since they often also suffer from a loss of hearing.

Digital v analogue

Hearing aids work by amplifying sounds for the users. Generally, they are digital. A minute computer processes sounds, enabling the aids to be customized according to the wearer's hearing loss. Sounds are separated into different bands, each processed separately to try to improve clarity.

The aids may have different settings to enable them to adjust to the conditions in which they are worn, such as a large or crowded room or a quiet home environment. Some models are equipped with a separate control box to avoid having to reach behind the ear to adjust the aid directly.

Most digital aids now have directional microphones. The microphones can be switched to amplify all-round sound or directional sound or may detect where the main sound is coming from and adjust automatically to reduce extraneous sounds.

On the whole, analogue hearing aids are confined to body-worn aids where a wire connects the earpiece to a box containing the microphone and mechanism, which is clipped to the body. Analogue technology is also generally used for bone conduction aids, used by those whose hearing loss is severe. In this case the sound is delivered through the skull in the form of vibrations.

Low take-up

A recent study in the United Kingdom carried out for Deaf Awareness Week revealed that 1 person in 10 with hearing loss is too embarrassed to wear a hearing aid. The UK's RNID (Royal National Institute for Deaf People) states that while 10 % of adults would benefit from wearing a hearing aid, just over 3 % of the population have one. In the United States of America, more than 32 million people, or around 1 in 3 adults, are estimated to have some degree of hearing loss.

The percentage is likely to rise as the population ages – and because of the prevalence of personal listening devices such as MP3 players. For the main part, these are played too loudly for too long – and their users are too young to appreciate the damage that is done to their hearing. Most youths don’t understand that hearing is not like an underused muscle. Once it's gone it can never be brought back into good shape.

Enhanced testing

While manufacturers endeavour to produce smaller, less obtrusive aids, work is also going on behind the scenes to improve test methods. This work is the remit of IEC TC (Technical Committee) 29: Electroacoustics. TC 29 underpins large areas of social, environmental, medical and rehabilitation work, which requires the accurate production and measurement of sound.

Leif Nielsen, Secretary of TC 29, says that for years there has been a series of hearing aid standards based on testing using pure tone sweep. "The standards are well-established and well-defined but not really representative of daily use," he says. After all, wearers of hearing aids do not spend their days listening to a series of electronic beeps.

"The available instruments and measuring methods still represent a high degree of simplification compared to the perception of noise by man and to the effect on the human ear," TC 29's SPS (Strategic Policy Statement) emphasizes.

Even so, great technological strides have been made that go far towards bridging this gap.

Hearing aid standards

TC 29’s WG (Working Group) 13: Hearing aids, is responsible for establishing standards to do with hearing aids. "We've been trying to get agreement on signals and testing that closer resemble daily use," says Nielsen. He adds, "A speech-like signal has now been developed."

Of course, the IEC's aim is always to produce standards that are applicable worldwide, so that manufacturers, wherever they are, can apply the same standard to their product. “Ideally, manufacturers should only need to carry out one test worldwide,” says Nielsen.

Increasingly, Nielsen sees that countries that have traditionally preserved their individuality by issuing their own standards are beginning to see the benefits of a more homogeneous approach. Global reach is now high on the list of many manufacturers' aspirations; it makes sense to have products that conform to a universal test requirement and that are ready for use anywhere.

"We're beginning to get there," he says.

Language differentiators

One of the main problems in producing a standardized test for hearing aids has been that the acoustic characteristics of languages differ markedly. This makes it hard to settle on a consistent approach in terms of signal processing applied to hearing aids. "Sounds, voices, languages, frequency content and pitch are very different," says Nielsen.

Given that another IEC aim is that standards should not take more than three years to pass through the various formal procedures necessary to ensure international agreement on a standard, the last two or three years have been spent at an informal level in technical development of the new test signal, he says.

Nielsen points out that it has taken up to 15 years to reach agreement on some standards. However, now that IEC 60118-15, Signal processing in hearing aids, has reached the CD (Committee Draft) stage, it is expected that publication can be finalized within the normal three-year time frame.

The IEC 60118 series of Standards forms the basis of performance specification and measurement for hearing aids. TC 29 has also been responsible for standardizing the performance of ear, head and torso simulators, enabling the relationship between subjective and objective measurements to be understood better.

Today, hearing aids are no longer simply standalone devices with linear amplifiers. They combine both a physical hearing aid and the relevant software, which is adapted to the needs of each user. The proposal for IEC 60118-15 therefore aims to provide a method to characterize hearing aids using a speech-like signal. The method described in the future standard is to be seen as a supplement to existing standards and will provide a better basis for developing and selecting the hearing aid best suited to each individual user.

Second draft

The second draft of IEC 60118-15 is already underway. "There have been 25 pages of comments," says Nielsen. Some of those comments have come from Canada, Japan, India and the United States of America as well as from Northern European countries that have a long tradition of association with work on hearing aids.

After this process, the revised draft standard will be put to the TC 29 Member Countries and experts for a second national consideration and comments. The proposal will be discussed again at the next meeting of TC 29, which is scheduled to take place in November in Tokyo. Nielsen expects voting at international level to begin in early 2010.

Wearers of hearing aids will undoubtedly benefit from this more natural approach to testing. They will be grateful to the engineers whose dedication to their work led to enormous improvements in maintaining humans' ability to communicate.