If I were to describe to you an analogue hearing aid with 1 channel that uses output compression limiting (basically peak clipping) you will probably think I am talking about a hearing aid from 40-50 years ago, but I may also be talking about the Phonak Lyric. Phonak have taken this old technology, shrunk it down to the size of a fingernail and brought it forward to the 21st century providing premium sound quality and amplification.
The Phonak Lyric is the most unique hearing aid on the market at present. This is because you do not purchase the hearing aid but instead you subscribe to a service. You will always have the latest model, and you would simply get a new one when the battery dies or the device fails. It is without doubt the most discreet hearing aid on the market and is more of a lifestyle choice than a purchase.
The Phonak Lyric stays in your ear for months at a time (average 2 months) and this can only be inserted by an authorised Lyric Partner. At present there are only about 60 out of about 2,500 private hearing centres in the UK that are trained and authorised to distribute Lyric. I am fortunate enough to be one of those individuals and I have been fitting the Lyric for about a year now.
The Phonak Lyric is controlled by a device called the SoundLync. The SoundLync is essentially a magnetic tool which interacts with the hearing aid when placed next to it and can adjust volume, switch off, and place it in sleep mode. Sleep mode still allows a natural amount of sound through whereas the off mode completely shuts down the Lyric and it would act as an earplug.
The volume control is somewhat cumbersome and requires the user to listen to a cycle of beeps to select the desired volume. The long-term Phonak Lyric wearers usually get the hang of it but it certainly takes time to remember the procedure.
There are some people who don’t use the SoundLync at all. Several patients of mine have dexterity issues which prevents them from using conventional hearing aids. This is because changing the battery and inserting the hearing aid in the ear requires careful coordination and control. For these people, the Phonak Lyric offers 24/7 hearing and is a solution which was before now unachievable.
Fitting Range and Technical Specifications
The Phonak Lyric is designed for people with mild-severe high frequency hearing impairment. It has an input range up to 102dBSPL which is lower than some of the other Phonak models but it means that for general conversation and moderately loud music it would not distort but louder music (such as a live event) may affect the quality of the output, which some of my customers have reported in the past. To overcome this, I recommend the use of a custom ear plug which reduces background noise and can be used alongside the Lyric. This is provided free of charge as part of your Lyric subscription if required.
When thinking about sound quality the Lyric could be compared to a vinyl record and a traditional digital hearing aid could be likened to an audio CD. Vinyl sales remain high even today in part, due to the belief that digital processing can’t replicate the richness and quality of an analogue vinyl recording.
Analogue Vs Digital
Sound is an analogue signal which means that it is a continuously variable physical quantity. Vinyl is also analogue because it uses a needle, whose mechanical movement is controlled by an audio input, to carve the waveform in to the record. CD is digital because it records using the binary system which is either 1 or 0. It requires sampling the sound and translating that in to binary code. The quality of the recording depends on something called the sample rate. The sample rate is the number of times per second a waveform is measured. A higher sample rate takes up more room on a CD because essentially it is collecting and storing more data. A lower sample rate saves space but then affects the overall quality of the sound.
Using the diagram above you can see that if we sample the original waveform at 10 points it keeps the shape quite well. When sampled at six points it is still recognisable but it is losing shape somewhat. Finally, the last depicts sampling the waveform at two points which loses a lot of the structure but you can still identify the peak and trough. Anything less than this and the waveform would be completely unrecognisable.
CD’s use a sample rate of 44.1KHz because the human ear can detect a sound up to a frequency of 20KHz and so will need a sample rate of at least double that to recognise the peak and trough of the waveform.
An average modern hearing aid has a sample rate of 20KHz which is relatively low compared to the audio CD. It means that to sample at least 10 points of the waveform, the frequency of the sound input would need to be 2KHz or lower. To sample at 6 points, the sound would need to be 3.33KHz or below and to sample at two points the frequency would need to be 10KHz or below.
Many hearing aid manufacturers boast about their 10KHz bandwidth but as you can see, the quality of the sound in the higher frequencies would be significantly reduced because of the low sample rate.
Why don’t hearing aid manufacturers increase their sample rate?
The simple answer is that it uses more processing power and decreases battery life. The trade-off for reducing the sample rate to introduce other useful technology is a compromise worth taking. As well as this, the person wearing a hearing aid is often unlikely to be able to hear much beyond 10KHz due to the impairment in their hearing.
You could conclude from this argument that the reason a lot of my customers are preferring the sound quality of Lyric is because it retains the shape of the original waveform. This is probably true to some degree as humans have evolved to process analogue information.
I haven’t proven it but I suspect that although perceived sound quality may be better with the Lyric, speech discrimination is likely to be better with digital. With digital processing sound can be broken down and amplified over many different channels making it more customised to your hearing loss. Complex algorithms can also be applied to improve speech in background noise along with effective feedback cancellation technology and wireless communication. In short, there is a reason analogue hearing aids are all but obsolete now and I’m sure Phonak will jump the Lyric over to digital processing as soon as the technology is available.
Proximity to Eardrum
I feel the main reason that the sound quality in Lyric is perceived to be so good is because of the proximity of the device to the ear drum. The Lyric sits just 4mm away from the ear drum which is likely to have a significant improvement on the acoustics. It is known that with shallow fitting hearing aids you can suffer from occlusion.
Occlusion can create the effect of an echo or hollowness in your own voice. This is due to the hearing aid blocking low-frequency body-conducted sounds from escaping the ear canal and instead they are reflected towards the ear drum. As such, the individual would hear their own voice through two different pathways and because one route is faster than the other an echo occurs. The way to reduce this is to either get a deeper mould past the cartilaginous portion of the ear canal and/or create a vent. Using this theory, the Lyric would be the equivalent of having a very deep mould and so occlusion does not occur.
As well as this, with Lyric being so close to the ear drum you also retain a lot of the natural acoustics of the ear itself. The ear naturally amplifies speech frequencies and localises sounds and so by having the hearing aid deep in the ear we retain a lot of these natural properties.
Fitting a Lyric is probably the most invasive procedure I do in my clinical practice. It required special training from Phonak and is without doubt a confidence product. Without conviction in your clinical decisions with Lyric you simply will not succeed with it.
There are many things that may prevent someone moving ahead with a Phonak Lyric but the most common issues I have encountered are around ear size, or ear shape. Having too small/large ears prevents many people from proceeding with the Phonak Lyric but now Phonak have announced the release of the XXS and XXL we should hopefully see an improvement in these statistics.
The Lyric is an analogue device without any feedback cancellation technology. It solely relies on the attenuation properties of the foam seals and the physical fit of the device in the ear canal to prevent feedback. As such, when the fit is poor feedback becomes unmanageable and either amplification is compromised or the Lyric is rejected by the wearer.
I for one feel that Lyric is a fantastic device for the right person. It suits a dynamic lifestyle and the sound quality is perceived to be generally superior to conventional hearing aids. Feedback and fitting issues are still very common but I hope over time these issues will be put behind us. In the meantime, there is no predicting if Lyric is right for you. You can compare it to Marmite I guess, you will either love it or hate it. If you are thinking about trialling Lyric, just go for it, it might be the best thing you ever did.
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