13/08/2009 by John Lloyd.

Lesson 1

What is a ‘digital’ hearing aid?

Firstly let me explain what ‘analogue’ is:

An analogue signal uses a physical medium to convey information. 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 requirements. This requires a micro-chip as in a computer.

To clarify:

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.

Computers are required to read this binary code. Digital Hearing Aids are effectively mini-computers possessing micro-chips, some of which can undertake 120million 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 (i.e. high frequency 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 raise the speech to noise ratio (we cannot completely remove sounds, as sounds do bounce off walls!)
Control feedback / unwanted whistling to a degree
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.

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’.

Cameras had 5 megapixels capacity last year but 10 megapixels this year; laptops had 120gigabytes of storage last year and 250Gb this year; hearing aids have 120million calculations per second this year, so what next year ….….?

One day feedback will be an issue of the past, background noise will be much easier to manage, and Bluetooth will open up a world of hearing solutions.

We must remember though, a person with a hearing loss has damaged hearing organs, and no matter how good a hearing aid becomes, the hearing organs are still damaged. We are not replacing the hearing, we are utilising technology to maximise the potential of the residual hearing.

I do hope this helps. Please add your comments or ask any questions.

(To follow soon: Lesson 2 - Hearing Aid Channels)

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01/08/2009 by John Lloyd.

The Phonak Naida is a new super-power hearing aid for clients with severe to profound hearing loss. Available at three technology levels to suit everyone’s budget and lifestyle requirements.

The Phonak Naida 9 is the first absolutely fully featured premium product in the super power segment, and offers all the features you would find in the proven top range aid the Exelia, including Bluetooth which enales much better hearing on the phone and the TV.

Also, using sound recover the Naida can restore lost regions of hearing by moving them to audible regions of hearing - this means we can now restore clarity of speech in the most profound high frequency hearing losses (it should be noted this can take some time to adapt to)

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