Hearing aids may seem like a specialist subject. But it's one that perhaps should be engaging all of us.
Not just because the world population as a whole is getting deafer younger. As the components and sensors in our phones become smaller and more numerous---and cheaper, many pundits believe these could eventually end up as an integral part of our bodies. Not necessarily surgically implanted—more likely temporarily housed in some body cavity. The ear canal is an ideal location.
It's happening already with the arrival in the consumer market of "true wireless" earbuds like the Optoma Be Free 8s. Manufacturers are already beginning to add further sensors like accelerometers and thermometers to devices like these. Earbuds capable of roughly assessing your hearing profile and adjusting themselves accordingly are on the horizon.
So consumer earbuds and specialist hearing aids may well be due for a collision. The hearing aid industry, currently dominated by six main manufacturers, each with its own highly proprietary system, seems to be headed for the same shake up that transformed the computer industry in the early 80s.
I CAME TO HEARING AIDS ONLY at the end of last year. I've probably spent the last decade oblivious of the gradual loss of the top frequencies of my hearing (which carry a large amount of the data that makes speech intelligible) thanks to the cunning ability of the human brain to "fill in the blanks" (see box below). But it's that same computational cunning that my new Teneo M+s are using to restore a much fuller appreciation of the soundscape around me.
The Teneo M+ has been adopted by the NHS as a standard corrective for mild to moderate hearing loss. The devices are manufactured by the German company, Sivantos, which was spun-off from Siemens Audiology Division in January of 2015. Siemens retains a stake in the new company and Sivantos continues to use Siemens branding for its products alongside its own Signia brand. Other brands associated with Sivantos and carried over from Siemens are Audio Service, Rexton, A&M, audiobene and HearUSA.
The Teneos are behind-the-ear (BTE) devices, each equipped with a pair of microphones and an output transducer (it transmits sound, but is, confusingly, usually known as a "receiver" through an ancient analogy with the telephone). The output is conveyed through a thin, barely visible translucent tube (Siemens chooses to call this a "Life Tube" for some reason) which terminates in a wider plug designed to lodge firmly in the ear canal.
From the several different optional designs of plug my audiologist settled on fitting me with a "semi-open dome" that offers minimal restriction between the ear canal and the air outside. This allows natural ingress for the lower frequencies below 1KHz that I have no trouble hearing.
This sort of dome seems to be the preferred option for mild to moderate hearing loss, although in this era of Bluetooth music direct from your phone it has its downsides, as we shall see.
You might think that in order to deal with hearing loss that starts to slope off above 1kHz, the Teneo M+s would progressively amplify those lost frequencies to straighten the curve. Back in the days of analogue electronics that was the only approach.
The snag with this is obvious when you understand that the loss of those top frequencies can be due to irreversible physical changes in the inner ear. The parts of the ear tuned to those frequencies may have mostly stopped working.
Modern digital hearing aids, like my Teneo M+s, are far more cunning. They can take those upper frequencies and transpose them down into the range of frequencies that the damaged ear can deal with much better. And this is where the importance of the brain function comes in.
If you did the same thing with an orchestra—told the wind section, for instance, to take everything down a couple of octaves—the result would be far from what the composer intended. But all the information, the melodic lines, would still be retained. And the harmonies, though modified, would still be essentially the same chord progressions.
Ears that fail to respond to the upper frequencies are hearing this orchestra through a low pass filter and will get a lot more information if the wind section carries out that transposition. The brain will have to do some work to make use of this new information, but adaptation of this kind is exactly what brains have evolved to do.
The official Siemens literature suggests that amplification, properly matched to the user's audiogram, should be the first choice if the pattern of hearing loss allows this. In my own case---mild to moderate age-related hearing loss---although there's a quite noticeable (on graphs and in real life) slope off at 1 KHz, there's still enough residual hearing above that frequency for amplification to be the preferred option. My audiologist tells me that the Teneo M+s mix in a small amount of frequency compression, so that a portion of those top notes will have their frequencies halved or quartered, to be mapped into the region just below 1KHz where I hear well.
This combination works well, although the brain needs time to adapt. When I first got my new hearing aids I found myself puzzled by new sounds I had at first taken to be artefacts of the devices themselves. That new strange persistent twittering noise I was hearing in my office. A rogue smoke alarm? Howlround?
It turned out to be the birds outside my window, something I hadn't heard for nearly a decade.
Inside the Teneos
A dozen or so preset programs are available for the Teneos. A choice of up to four of these, tailored to my audiogram by the audiologist, can be allocated to four program slots. The user picks any one of these four programs to suit the current environment using one of the rocker switches. These are my four:
♦ The main program is Auto. As its name implies, it's designed to tune its profile in response to the immediate soundscape. It does a useful job dampening the howlround that can occur when output from the "receiver" feeds back into the microphones. It detects and virtually eliminates wind noise when you're out and about. And the Auto function includes the detection and amplification of speech frequencies to help separate the human voice from the surrounding hubbub. Extraneous noise from all directions is tuned out as much as possible.
♦ In particularly noisy surroundings I have the option of switching to the second program, Noisy. This uses the virtual 8 microphone array (see below) to create a focus area immediately in front of me, the aural equivalent of tunnel vision. Sounds coming from behind me and from the sides are suppressed so that I can concentrate on my conversation with the person I'm facing.
♦ The program my audiologist has installed in the third slot is Loop, designed to pick up transmissions from any T-Loop system. T-Loop, sometimes called telecoil, is an audio induction system installed in many public buildings and transport vehicles. It uses one or more cables circling a designated area within which it creates a magnetic field whose modulations can be picked up by suitably equipped hearing aids. It's a simplified, large-scale variant of NFMI (see below).
My own Loop program connects to T-Loop while still keeping the microphones open. As an optional alternative, if the user finds ambient sounds distracting, the audiologist can choose a program that mutes the mics and accepts input only from T-Loop.
♦ Initially, my fourth program slot was left empty. But on my second visit, once I was more familiar with the Teneos, I asked if there was a program more appropriate for listening to music. The Auto program wasn't objectionable, but for music in a concert hall or one's own living room, noise suppression is generally unnecessary and can create unwanted artefacts. And Auto also introduces variable gain control (VGC) that continually adjusts the overall volume, detracting from the dynamics of the music..
My audiologist accordingly installed the Music program in this fourth slot. This minimises noise cancelling, VGC and howlround protection with the aim of presenting the music with as few artifacts as possible.
Physically and electronically the two Teneos are identical. It's only after they've been programmed by the audiologist and fitted with the appropriate left- and right-handed Life Tubes that they become a matching pair.
More expensive, smarter hearing aids aim to adjust automatically to almost any kind of soundscape, able to detect music in a concert hall or a living room, ameliorate echo in over-bright acoustics, and adapt to conversation coming from different directions. The scope of the Teneos is limited in this respect. But the ability to switch manually between these four programs (and with the help of the audiologist substitute different programs where necessary) goes a long way to making up for this.
If the volume control on one can also change the volume on the other, you might well be wondering—I certainly was—how these two tiny devices communicate with one another. If you're thinking of a wireless connection along the lines of Bluetooth, you'd be wrong.
Operating at a frequency of around 2.4 GHz, the same as a microwave oven, Bluetooth would boil your brain cells. Well, perhaps not quite—not at the very low power levels that Bluetooth employs for communication, around 1000th of the power of a microwave oven.
Bluetooth would still try to boil your brain, but in failing miserably lose so much power that its signal couldn't be guaranteed to reach the opposite ear.
Hearing aids like the Teneos communicate with one another through Near-Field Magnetic Induction (NFMI), a wireless communication channel that relies on the magnetic rather than the electric component of electromagnetic radiation. Its power requirements are tiny, around a tenth of what Bluetooth needs.
NFMI, as used in the Teneos, operates in the MHz spectrum. Its reach is very much shorter than Bluetooth—think of a bubble around your head with a radius no larger than arm's length. Exactly what you need for a body-sized private network.
One important function of this fast, through-the-skull connection is to coordinate the Teneo's microphones. There are two of these in each hearing aid, one immediately above the rocker switch and the other at the top of the device where the Life Tube screws on. The Life Tube screw-on base includes a small vent for the microphone to listen through.
The Teneos use their NFMI connection to handle these four mics as an array of four different stereo pairs. The left and right rocker switch mics form one pair, the two Life Tube mics another. The left rocker switch mic and the right Life Tube mic are another pair, and so on. An array of eight virtual mics in all. This array gives the Teneos a very good idea about where the surrounding sounds are coming from, helping them to distinguish noise from useful information and pass on directional hints to the wearer (but see the caveat below).
Wearing and Hearing
More importantly for me, I can hardly feel they're there and find myself occasionally reaching up to touch them with my fingertips to make sure they haven't fallen off. (They never have.)
I was surprised to find they still fail to make their presence felt even when I'm wearing glasses. More surprised yet that I can put a pair of my Bose QuietComfort headphones over the combination of Teneos and glasses without any unwanted sense of extra pressure. It's almost as if ears were designed to have these things snugly installed behind them.
Unfortunately, the real function of the ear flaps---pinnae, to give them their scientific name---is somewhat at odds with this positioning of the Teneos. The convolutions of the pinnae have evolved to help us detect with remarkable precision the locations of the various sounds in the space around us. If you hear a twig snap under the paw of a tiger stalking you in the jungle, it's life-enhancingly useful to know exactly where that sound is coming from.
The higher frequencies carry most of this location information. It's unhelpful that it's exactly these frequencies that are now largely reaching my brain through pairs of microphones placed behind the pinnae. The electronic processing is also introducing a slight delay in the arrival time of these frequencies. It's only a few microseconds, but triangulating with interaural time difference (ITD, the lag between the arrival of the same sound at each ear) is another very important factor in localisation and it is indeed measured in microseconds.
This helps explain my initial confusion about the twittering sound in my office. Because I couldn't at once locate the origin as being outside my office, the brain wasn't easily able to equate the sound with birdsong.
Location, Location, Location---this is one of the few downsides of behind the ear devices. Much more expensive hearing aids that fit entirely into the ear canal preserve natural ITD much better. And all the device form factors can ameliorate this problem with faster (but costlier) processors.
Many of today's premier hearing aids pride themselves on having Bluetooth incorporated. A direct link to your iOS or Android device seems tempting, and I must confess some initial disappointment that the Teneos lacked this feature. But now I understand the technology better, I think the way the Teneo designers handle Bluetooth---outside the devices themselves---has a lot going for it.
It's a cost option, and not a particularly cheap one. But for UK NHS users the £280ish price of the easyTek neck loop device brings the total cost of the system up to, well, £280ish. A relatively small price to pay in a market where the ticket for a similarly featured set of commercial hearing aids will probably run into several thousands.
The easyTek hangs round the neck like a much more discreet version of a Lord Mayor's Chain of Office. Its basic function is to substitute for the on-device rocker switches, so pressing on the large central button will switch between the four programs, while a pair of secondary small push buttons set into the right side control the volume. A long press on the central button turns the easyTek on or off.
Bluetooth is switched on by holding down the central button in conjunction with the upper secondary button. Once paired to a Bluetooth device like a phone the easyTek will take over as the phone's audio output. The stream is then relayed directly into the hearing aids through the neck loop-to-Teneo NFMI link.
The easyTek is large enough to incorporate a relatively high-capacity battery, topped up daily with the microUSB charger supplied. Bluetooth streaming like this adds no drain to the tiny zinc-air batteries in the Teneos.
It was this factor that dispelled my initial disappointment at discovering the Teneos themselves aren't Bluetooth-enabled. Bluetooth, even the so-called "Low Energy" version (BLE), soaks up ten times the juice of NFMI. Manufacturers will tell you with a straight face that the batteries in their new Bluetooth-enabled hearing aids last as long as the previous generation. This may be the case---as long as you don't use them for Bluetooth streaming!
No special additional program is needed for the Teneos. Once the presence of the easyTek is detected the Universal program picks up the connection. I found that, once paired to my Huawei Mate 9 and my nVidia Shield the easyTek would (mostly) automatically switch on Bluetooth and connect to either or both of these devices as soon as it sensed their Bluetooth presence.
(On the occasions when this failed I found it necessary to switch off the easyTek and then switch it on again.)
This automatic connection to both devices comes in handy when, for example, I start watching a YouTube video on my phone and decide to Chromecast it to the Shield. I was very pleasantly surprised to discover the easyTek (usually) effortlessly transfers to the Shield's Bluetooth audio transmission.
If all you need the easyTek for is as a handy way of controlling the Teneos without having to reach up behind your ears---and you have an Android or Apple phone---there's a no-cost alternative. The free TouchControl app will let you switch the Teneos on and off, swap between the four programs and control the volume.
Your phone, of course, doesn't do NFMI (although the NFC feature increasingly popular for electronic payment uses a very similar approach). So you may be wondering, as I was, how it communicates with the Teneos.
Hearing aid like the Teneos are designed to operate in the relatively narrow (in hi-fi terms) frequency range of 250Hz to 8kHz---because the science of audiology has grown up around the primary need to make speech intelligible---and the output through what I suppose we are going to have to get used to calling the "receiver" is limited accordingly. But it turns out that the tiny microphones have ideas well above their station.
They can detect ultrasound, frequencies in the region of 20kHz, the upper limit of human hearing. Your phone's tiny loudspeaker can also operate in this range. So although you won't be able to eavesdrop on the instructions your phone is squeaking out to the Teneos, they get the message.
If you do decide to lash out on the easyTek, there's an app for that too. The app (just called "easyTek") does everything the touchControl app does. But because it establishes a two-way Bluetooth communication with the easyTek device (and onward to the Teneos through the two-way NFMI link) it's able to report on the state of the Teneos batteries, left and right, as well as the amount of juice left in the rechargeable easyTek.
The easyTek seems also to have a tone control. It's not mentioned in the easyTek manual, and I couldn't find any way of operating it from the physical buttons. But it appears in the easyTek Android app as a slide bar labelled SOUND BALANCE with Bass and Treble markers at each end. I discovered that pushing the slide bar all the way over to the left, Bass end subjectively improved listening to music through the easyTek. Which brings us to…
There's a huge catch to the use of the easyTek—or any Bluetooth in this context—which becomes apparent immediately you start using hearing aids for listening to music. But before we get on to that, we need to take a look at the nature of the domes used to terminate the Life Tubes and lodge them into the ear canal.
Open domes became popular over the last 20 years as a perfect solution for typical age-related hearing loss like mine where only the upper frequencies need to be amplified and/or shifted. The lower frequencies that I hear perfectly well are allowed to enter the ear naturally. This preserves directionality to some extent and avoids the occlusion effect which would make my own voice sound unnaturally enclosed and boomy.
Before the 21th century, closed domes or tailored earmoulds would have been used in these circumstances. Effectively all frequencies would pass through the hearing aids, with natural sounds of all frequencies being blocked out. Closed domes are used today primarily for wearers who need correction across the whole range of frequencies.
With BTEs like mine, closed domes would move the total focus of my hearing from my ear canals to the microphones behind my ears, destroying the pinna effect and so removing a large part of the natural clues to the location of the sounds I was hearing.
As I've mentioned, my own domes are technically "semi-open" (see illustration), sometimes called "tulip" domes. These fit reliably and comfortably into the ear canal while still letting through the lower and mid-range frequencies. For the most part they behave like open domes.
Open (and semi-open) domes, then, are the aural equivalent of augmented reality (AR), with the hearing aids superimposing their own (upper frequency) modifications on my real-world perception. Closed domes instead offer me virtual reality (VR), a totally computer-reconstructed representation of the soundscape.
For the past couple of decades the adoption of open domes in cases like mine, augmenting rather than completely virtualising reality, has made a good deal of sense. But in recent years the application of hearing aids has been expanding. Bluetooth streaming, either built into the hearing aids or supplementing them with accessories like the easyTek, is rapidly becoming a required standard function.
This is a game changer. When the entire soundscape is being streamed into the ears electronically, AR no longer does the job properly. Only the upper frequencies are catered for. The lower frequencies, which in ordinary hearing aid use pass through open domes mostly unaltered, are now missing. A Mozart string quartet can sound as if it's being played on a banjo.
Is this fixable? Not, it seems with currently available hearing aid technology. But if I'm right about the medical and consumer branches of the ear wear business coalescing (and this is happening now), we're going to need dual-mode domes capable of switching programmatically between open and closed. A promising field for this may be micro electromagnetic systems (MEMS), the magic behind the "dancing mirrors" in DLP projectors.
In practice, Bluetooth streamed to the easyTek with my semi-open domes is a combination that turns out to work perfectly well for watching news on television. Movies and TV series where music plays a large part take a bit of getting used to. But if the story is gripping enough I'm happy to live with the loss of bass (which, in any case, helps to keep the dialogue intelligible). With action movies and computer games you're definitely going to miss the booms and bangs, even with that Sound Balance slide bar pushed far over to the Bass position.
I was frankly amazed at how well these shrimp-sized miracles work. I've been a "computer guy" for nearly 40 years and have watched, cheering from the sidelines, as the technology shrank from clunky desktop machines to powerful pocketables. But these developments in audiology came as a brand new surprise.
Birdsong, the creaking floors in my house, the flutey overtones of high-flying aircraft—the Teneo M+'s augmentation of my top three octaves restored all these. And my family stopped mumbling.
And it quickly struck me that, even if my hearing were 20:20, these things would still be handy. While the Noise program doesn't always fully deliver the goods in lively get-togethers, it certainly helps and would have been a boon back in the day when my ears were young. Being able to tune down a noisy live concert or set preferential focus on the dialogue in an over-orchestrated movie would be an advantage for anyone's hearing, impaired or not. On top of that, there's the advantage---thanks to the easyTek---of having the freedom to watch videos on my phone without annoying others in the room or having to put on headphones. Everyone could benefit from bionic ears like mine.
So get ready for the emergence of commodity full-featured "earwear", offered with consumer-useful programs but also optionally tuneable by a qualified audiologist.
So my music experience is still suboptimal. Tough. But I can't help thinking that Beethoven would have killed for a pair of these.