There are different types of hearing aids, but they all have the same five key components:

  • microphone – detects sound waves as they enter the ear, converts them into digital signals and sends the signals to the amplifier
  • amplifier – strengthens the digital signals
  • microchip – a miniature computer that helps us tune and personalise your hearing aid to your individual needs
  • speaker – converts the digital signals back into sound waves that continue via the inner ear to the brain
  • a tiny battery to power the hearing aid

You might think hearing aids are just amplifiers but it’s not quite that simple! Amplifying all sounds by the same amount is not what most people with hearing difficulties actually want.

Digital hearing aids use a combination of different techniques including:

Gain adjustment

The amount by which an amplifier increases a particular frequency (or band of frequencies) of sound is known as its gain. Digital hearing aids adjust the gain selectively, typically for about a dozen different frequency bands, to match a person’s particular hearing loss. Gain adjustment is a bit like the graphic equalizer on a stereo, where you can turn different frequency bands up or down to emphasize speech, treble, bass, or particular instruments.

Compression

This is a key feature of digital hearing aids. Although it’s complex, and there are numerous different kinds, the basic idea is simple. A person with normal hearing can hear the full range of soft and loud sounds (from falling leaves to jets screaming overhead) for all frequencies, but someone with a hearing impairment will only hear sounds at those impaired frequencies if they’re loud.

The hearing aid needs to squeeze (or compress) the range of soft and loud sounds in the world around us into the much smaller range that the person can actually hear. This is complicated by the fact that the amount of compression required is different in each frequency band.

Speech enhancement

This selectively boosts sound frequencies in the range from a few hundred to a few thousand hertz, which carry most of the energy in human speech. Modern hearing aids are able to apply this extra boost to a particular frequency band when speech is detected in that band.

Binaural synchronisation

A hearing aid on one ear will wirelessly communicate with a hearing aid on the other ear to synchronise adjustments, ensuring a balanced sound. This function also allows the hearing aids to detect differences in sounds reaching each ear which helps to localise sounds in space.

Sound classification

This categorizes the sounds you can hear into music, speech, or noise and amplifies them (or reduces them) selectively. Sophisticated hearing aids effectively figure out what kind of environment you’re in (watching TV, noisy restaurant, lecture theatre with distant speaker) and apply a different amplification pattern to the sounds you’re hearing. It is like having a magic pair of spectacles which can selectively magnify specific colours:

Digital hearing aids