So what, exactly, is a hearing aid? A hearing aid, also called a hearing instrument, is a highly sophisticated communication device. There are many different types of hearing aids, just as there are many forms of hearing loss, but they share some basic components. All of them work on amplifying sounds to enhance particular hearing range problems but it’s more than just a noise amplifier. The design of each hearing instrument can vary but the overall effect is to empower you to live your life to the very fullest.

A hearing aid works basically like this:

  • A microphone picks up sounds.

  • Sounds are analyzed by a processing chip.

  • Processed sounds are sent to the amplifier.

  • Amplified sounds are sent to the loudspeaker.

  • Sounds are transmitted by the loudspeaker into the inner ear where they are transformed into electrical impulses.

  • Impulses are picked up by the brain where they are processed.

This is a far cry from the early “ear trumpet”!

Hearing Aid Technology

In all hearing aids, sound enters through a microphone. It is then processed, amplified, and delivered to a receiver (loudspeaker). This sends the output either directly to the user’s ear canal, via tubing to an ear mold and into the ear canal, or via a thin wire to a receiver placed directly in the ear.

There are two types of sound processing:

  • Analog

  • Digital

Analog Hearing Aids

Analog sound is like making a photocopy: the sound is registered and you get an overall picture. But the actual processing is analog insidelike recopying a photocopy – it can only be done to a certain extent because it causes a deterioration of the original imprint. Analog hearing aids have a microphone which picks up sound in the environment and converts it to small electrical signals. The electrical signal is then amplified and shaped by transistors and circuits in the signal processing part of the hearing instrument. Shaping and output limiting are performed by manual adjustments usually located on the outside of the hearing aid faceplate. The amplified and shaped electrical signal is then sent to the receiver to be changed back to an acoustic analog signal and sent to the ear of the hearing aid wearer. Analogue hearing aids can have many complex circuits at the signal processing stage but there is a limit to the number and tends to cause interference.

Digital Hearing Aids

Digital hearing aids are much more advanced than analog or programmable hearing aids. In a digital hearing aid the acoustic signal is converted into digits (0, 1), processed within the hearing aid, and then reconverted to an analogue acoustic signal for the listener. A digital signal can be repeated endlessly without affecting the overall quality. It is like making copies of a scanned image: each copy is a perfect duplicate of the original. Because the code also includes information about a sound’s pitch or loudness, the aid can be specially programmed to amplify some frequencies more than others. These programs allow the hearing aid to function differently in different listening situations for example:

  • In a quiet conversation

  • At a concert

  • At a party where there might be a great deal of background noise

Digital hearing aids transform the analog information from the microphone into a binary code then the signal is taken from the microphone and transformed into data that can be manipulated by a tiny computer in the hearing aid. The data can then be tailored and processed very precisely and in ways that are impossible with analog aids. Digital hearing aids can be very finely adjusted to suit an individual’s hearing loss and can include features like noise cancellation, speech recognition and feedback suppression systems.

Analog/Digital Hybrid (also called Digitally Programmable Hearing Aids)

These aids use analog signal processing at the amplifier stage. However, they also have a digital chip at the amplifier stage that allows shaping of the frequency response and output-limiting to be altered by a computer rather than a screwdriver. Unlike a strictly analog hearing aid, a digitally programmable hearing aid allows for the choice of different programs from the internal memory to suit different listening conditions.

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