Firstly what is ‘analogue’?  – An analogue signal uses a physical medium to convey information from input to output. So for sound, fluctuations in air pressure strike the diaphragm of a microphone which then causes corresponding fluctuations in the voltage (or current) of the connected electrical circuit. The voltage (or current) is said to be an “analog” of the sound. These voltage fluctuations are passed through an amplifier to give greater voltage which is passed through a speaker and thus the sound is made louder. Old analogue hearing aids invariably just made sounds louder, and had a volume control so the wearer could regulate the volume of the hearing aid to suit the volume of the environment they were in. i.e. They would turn it up to hear soft / moderate sounds which they struggle to hear, and turn it down in loud environments because upper loudness thresholds are typically normal (or even hyper-sensitive).

To produce a ‘digital’ signal the originating sound pressure strikes a microphone and the resulting analogue signal instead of being passed through an amplifier, is ‘digitised’ by being passed through an electronic device called an analogue-to-digital convertor, which builds up a stream of sequential numbers (binary code) which can then be stored, manipulated and then reproduced according to specific and exact sound output requirements. This requires a micro-chip.

The word digital comes from the same source as the word ‘digit’ and ‘digitus’ (the Latin word for finger), as fingers are used for discrete counting.

‘Digital’ is simply a form of processing a signal, and for this process we use binary code.

Binary code is the numerical representation of a signal using streams of only two digits; 1 and 0; where 1 = pulse present and/or high, and 0 = pulse absent and/or low.

Computer programmes then read this stream of binary code to analyse and manipulate the data to give us predetermined results.

An analogue hearing aid takes in an analogue signal (sound wave), amplifies it, and sends it out via a speaker in exactly the same form, but louder.

A digital hearing aid takes in an analogue signal (sound wave), coverts it to digital signal (binary code), modifies the code/signal, and then sends the modified signal out in analogue form via a speaker. Microchips are required to read this binary code.

Digital Hearing Aids are effectively mini-computers possessing micro-chips, some of which can undertake many multi-millions of calculations per second – what we call processing speed.

The advantages of this digital processing over an analogue signal is that we can:

• Give the exact amount of amplification at each frequency to suit a persons particular hearing loss.
• Reduce the amplification of background sounds, i.e. steady state background noise such as air conditioning, traffic, aircraft noise etc.
• Use directional microphones to help focus the directional responce and improve the speech-to-noise ratio.
• Control / reduce feedback (whistling of hearing aids).
• Automatic volume control – as sounds get louder the amplification automatically reduces.
• Use frequency shifting technology to restore lost regions of sound by transposing or compressing them into audible regions of sound.
• Reduce echo reverberant sounds and wind noise.
• Have autopilot settings so the hearing aid analyses the environment the wearer is in and changes the above settings to suit each persons preferences.
• Incorporate digital streaming technology – i.e. stream phone calls, TV signal, zoom calls, music, and third party voices.
• And a host of other technology associated with streaing technology – i.e. language translation, fall alert, etc.

Digital technology is advancing at unbelievable rates. Microchips double in power and speed and computer memory doubles in capacity every 12-18 months – this is called the ‘cycle of innovation’ , or more commonly ‘Moore’s Law‘.

What does this mean for you? – the more powerful and faster microchips become, the more refined the sound output results are – giving you better hearing, especially in difficult listening environments. It also means we can programme hearing aids to work fully automatically for you, or we can give you more control for when you really need it. We can customise hearing aids to suit each person.

You must remember though, a person with a sensori-neural hearing loss (i.e. presbycusis / nerve damage) has damaged hair cells, and we are not fixing this problem – we are working with it. So, no matter how good a hearing aid becomes, the hearing organs are still damaged and we cannot restore normal hearing, especially in noise as the damaged organs struggle to differeniate and separate complex sounds. We must also remember that as we age our processing capability slows down and this also prevents a hurdle with hearing in noisy environments.

Let us look inside a digital hearing aid!

The outer casing is designed on computer and 3D printed from a resin compound material which is set in shape with laser technology (in the picture it is a black shell).

From left we have the battery door housing a zinc air battery – zinc air batteries are designed not to fade out in performance but to die quickly – you don’t want a hearing aid that fades in performance. Many hearing aids are now using lithium-ion rechargeable batteries. Compare all rechargeable hearing aids here.

In the faceplate we can have a push button for programme changing (e.g. for restaurant noise control) and for volume control (with hearing aids that have inter-ear wireless technology – NMFi). A volume wheel can be added but most people find these difficult to use and mobile phone apps have rendered these defunct in most cases.

O-Caps – for Oticon in-ear hearing aids these are replaceable microphone covers – they are very fiddly to change but your Audiologist can help and it can save the hearing aid from being sent in for repairs.  Not all hearing aids have replaceable microphone covers.

2.4Ghz signal wire – this allows hearing aids to connect wirelessly to other device – i..e mobile phones, TV streamers – for greater speech clarity.

Microphones – to pick up the sound signal – many hearing aids have dual microphones as this is the best proven technology for hearing speech in noise.

Microchip – the power behind it all – the processing ability of the hearing aid to digitise sound and help you hear better.

NMFi – Near Field Magnetic Industion. As mentioned a small part that allows inter-ear wireless technology so you can control both hearing aids from one side, but also allows data transmission of the amplified / processed sound to improve localisation of sounds. NMFi also allows older hearing aids to connect to neckloop worn accessories.

Receiver – receiving the signal from the microchip – a speaker to most of us!

Receiver suspension – a soft housing part to prevent speaker distortion.

Pro-wax mini-fit – for this Oticon hearing aid this is their wax guard solution – a means of unblocking wax ingress without having to send the hearing aid in for repair. Most hearing aids now use replaceable wax guards.

IP68 rating – this tells us how well protected the hearing aid is from dust and moisture.

In some other larger hearing aids you may also find a telecoil loop receiver – this allows hearing aid users to connect to telecoil loop systems in churches and theatres – this massively helps overcome distance problems for hearing speech. 

That is all for today!!