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There has been great excitement about the advent of digital
hearing aids, but many people remain in the dark about the
ways in which digital aids differ from conventional analogue
hearing aids. Digital hearing aids might not be smaller,
are not necessarily automatic and might not give benefit
to everyone with a hearing impairment.
Some of the digital hearing aids currently available.
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Like conventional analogue hearing aids, digital hearing aids have a microphone to detect the sound and a receiver to deliver the amplified sound. However, instead of internal components for filtering and limiting the sound, there is a digital signal processor or mini-computer. The incoming analogue sound signal has to be filtered, sampled and converted to a series of numbers. Then the digital signal processor processes the sequence of numbers to perform specific operations to filter or compress the sound. The hearing aid is programmed to the user's requirements using a computer.
The reduction in internal mechanical and electronic controls increases the available space for other essential components and might well increase reliability. Each digital hearing aid can be programmed in many different ways. This means that fewer models are required to meet the needs of the infinite variety of hearing impaired patients that are encountered. It should be noted that digital hearing aids use many of the features that are found in commercially available analogue aids. With digital processing, it is easy to incorporate several programmes for different listening environments. In addition, it is much easier to introduce signal processing strategies, such as those aimed at improving speech in noise, reducing feedback or maintaining the sound at a comfortable level. There is some 'cost' to all these advances. Some digital hearing aids introduce additional sounds used in processing that can be annoying if audible. Some users do not like the fact that those aids that are set to automatic programmes are constantly changing their output in different situations.
First, digital hearing aids might not bring significant benefit to everyone. For many people, the benefit attained from a hearing aid will be limited by how much damage there already is to the inner part of their ear (the cochlea). Often with cochlear hearing loss, in addition to loss of sensitivity, there can be poor discrimination - in other words, poor clarity and a blurring of sounds even when amplified. In such cases, any potential benefits given by digital aids might be irrelevant. In particular, digital aids might not be appropriate for those who have a severe or profound hearing loss. Second, how well a digital hearing aid performs depends on how well it has been programmed. For the professionals involved, fitting digital hearing aids can be a time-consuming task. Research must be continued to find the best methods to fit and fine-tune digital aids.
Digital hearing aids seem to offer great potential. However, many of the claims made about digital hearing aids have not been investigated and validated by scientific trials. Further research is necessary to determine which elements of new technology give measurable benefit to the user.
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