New Zealand Association of Independent Audiologists
What are "Digital" Hearing Aids?
Digital hearing aids are, in essence, miniaturized computers. They convert sound to an electrical signal, and then to a digital signal, a numerical code that represents the intensities and frequencies of the original sound.
The digital signal can be processed to meet the person's needs and then converted back to an electrical signal and then to sound. While earlier hearing aids were adjusted with a screwdriver, digital ones are programmed by a computer.
In conventional hearing aids, known as analogue models, the sound is converted to an electrical signal but never to a digital one. Some analogue devices do, however, employ digital technology to modify the electrical signal.
Like the fully digital devices, they can be programmed to alter the signal specifically to compensate for a particular type of hearing loss. But those models are referred to as "digitally programmable," and the term "fully digital" is generally reserved for hearing aids that convert the sound itself to a digital signal.
An estimated 400,000 New Zealanders have hearing losses, but only about 20% wear hearing aids. Many, with hearing losses ranging from mild to severe, are candidates for digital devices, though not every patient who meets those criteria will find the new models superior to other types of hearing aids.
Digitally programmable hearing aids have been available for about 10 years, and one of the advantages they share with fully digital types is that they cause far less distortion than many analogue devices. In addition programmability allows access to a greater number of controls than would be available on an analogue device.
Fully digital hearing aids also greatly reduce feedback, the annoying whistles that occur when amplified sound is fed back into the microphone.
Research on the use of directional or multiple microphones may ultimately lead to the greatest advances in helping people to hear speech in a noisy environment.
Certainly the potential for digital hearing aids is outstanding. But it would be a mistake to think that just because a hearing aid is digital it's automatically going to be better than the other devices out there. We have some good analogue and digitally programmable analogue hearing aids that are not going to be made obsolete immediately.
Indeed, older programmable hearing aids held their own against one of the digital models in a recent study by Dr. David Fabry, an audiologist at the Mayo Clinic in Rochester, Minn. and Dr. Michael Valente, of Washington University in St. Louis. The study included 60 patients who compared their programmable models with digital ones.
"We evaluated the individual's performance in background noise," Fabry said. "We found that there were no significant differences in performance between the two types of devices."
Even so, he said, "a considerable number of patients preferred digital sound to the analog." Many found the digital hearing aids to be better at picking up very faint sounds. "There is no question," he said, "that digital is the way of the future."