The Technology of Hearing aids:
Analog vs. Digital
Technology Types:
Hearing aids are are built from analog or digital circuits. Each technology processes sound differently. Until recently, all hearing aids were analog. Digital hearing aids are the newest kind of hearing aid and are superior to analog.
Analog vs. Digital:
All hearing aids, whether analog or digital, are designed to increase the loudness of sounds reaching the ear drum so that the hearing-impaired person can better understand speech. To accomplish this, hearing aids require three basic components:
1. A microphone to gather acoustic energy (sound waves in the air) and convert it to electrical energy.
2. An amplifier to increase the strength of the electrical energy.
3. A receiver, which is like a miniature speaker, that converts the electrical energy back into acoustic energy (sound waves). What makes digital hearing aids different from analog hearing aids is what happens in between.
Analog Hearing Aids:
Photo courtesy Unitron Hearing
Analog hearing aids use a continuously varying electrical signal to produce sound, just like a microphone and loudspeaker. Analog hearing aids have a microphone that picks up sound and converts the sound into small electrical signals. These signals vary according to the pattern of the sound. The signals are then amplified (made louder) by transistors and fed to the ear phone on the hearing aid which is next to your ear drum so you can hear them. Most of the better analog hearing aids compress the sound using 'automatic gain control" (AGC). This amplifies quiet sounds until they are loud enough to be heard, but gives less amplification to sounds that are already loud, so you're protected against uncomfortably loud sound levels. Analog hearing aids don’t have all the features that come with advanced digital aids, but they are
less expensive.
Digital Hearing Aids:
Photo courtesy Unitron Hearing
Digital aids take the signal from the microphone and convert it into "bits" of data - numbers that can be manipulated by a tiny computer
chip in the hearing aid. This makes it possible to tailor and process sounds very precisely in ways that are impossible with analog aids. The
digital chip takes the bits representing the sound
and analyzes and manipulates them using what is
called DSP or Digital Signal Processing.
Software algorithms (a set of instructions), are
used to perform the precise complex DSP
actions, and are then converted back into
electricity, which is finally changed back into
sound that goes into the ear. This process
happens very rapidly with several million calculations occurring in the hearing aid
each second.
The digital sound
representations can be manipulated in almost any way imaginable, and this is what gives the digital hearing aid its big advantage.
Reducing
background noise
When someone talks to you, you usually want to hear what they are saying, rather than whatever noise is going on in the background. People who use traditional analog hearing aids often complain that they find it difficult or impossible to follow conversations in noisy places.
Many digital aids are designed to reduce steady kinds of background noise, such as
crowds in a restaurant or the rumble of traffic or the whirr of a fan. This makes listening more comfortable. But it does not necessarily help you to pick out a single voice from everything else that's going on, especially when several people are talking.
Loud noise
protection
Some digital hearing aids also have circuitry to
protect whatever hearing is left. If a loud
sound is detected above the 90-100 Db range
(which can cause damage), dampening circuitry
cuts out the sound.
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