Before the development of digital aids, all hearing aids were analogue. Analogue aids use a microphone to pick up sound and convert it into electrical signals. The signals are then amplified by transistors and fed to the microphone so that the person using the hearing aid can hear them. The better analogue hearing aids used to compress the sound, automatically altering the gain to suit the incoming sound. This amplifies quiet sounds until they are loud enough to be heard, but gives less boost to sounds that are already loud, so that the person using the hearing aid is protected against uncomfortably loud sound levels. The idea behind this is that it should help the wearer when in very noisy places to hear the one voice or sound that he or she is interested in. Unfortunately, even with the better analogue hearing aids, this did not work very well and analogue hearing aids have been almost completely superseded by digital technology.
Digital aids work on a completely different principle and strive to overcome the problem of hearing against background noise. They take the signal from the microphone and convert it into binary coding – “bits” of data – numbers that can be manipulated by a tiny computer in the hearing aid. This makes it possible to monitor incoming sound signals and process very accurately. The best digital aids can be very finely adjusted to suit individuals lifestyles and hearing loss, they can be set up to automatically adjust themselves to suit different sound environments.
The major hearing aid manufactuers in Europe and the States have invested hugely in research and development of digital hearing aid technology. Much effort has been focused on the improving hearing in difficult listening enviornments, to help hear conversation in traditionally noisy places such as pubs or clubs etc.
Digital hearing aids are programmed by computer software at the point of fitting, using your personal audiological data and lifestyle choice. The hearing aids are normally set to an “easy listening” aclaimitisation level intially and then over the next few appointments, adjustments are made and the aclimatization levels increased until you are at your optimum setting. This is a very gradual process to help your brain cope with the new sound inputs.
Hair cells in the inner ear must pick up the vibrations that the hearing aid sends and convert those vibrations into nerve signals. So, you need to have at least some hair cells in the inner ear for it to work. It is important to remember that despite all the research, development and technology that is applied to hearing aids, full, natural hearing cannot be restored.