How to Improve the SNR in Children with Mild to Moderate Hearing Loss

In this video, taken from the 3rd Annual Trends in Pediatrics course held in May 2022, you will learn how to use and verify FM systems and remote microphones to improve the signal-to-noise ratio (SNR) for children wearing hearing aids.

You can read the full transcript below.

What are FM systems (radio aids)?

Jack Bennett: In this final section, we will discuss other systems that can be used to improve the signal to noise ratio for children with mild to moderate hearing loss.

For most children with a mild to moderate hearing loss, they will perform perfectly well in a classroom setting that is small or quiet. If however, that classroom setting becomes more busy, noisier, or a particularly large room, they might may actually find it much more difficult.

For these cases, there are systems that are used to improve the signal to noise ratio. These systems are often referred to as FM systems or radio aids. Generally, they will work in the same way, the teacher or target speaker will wear a transmitter, usually as close as possible to the mouth and the child will wear a receiver.

This could be integrated into the hearing aid, could be a shoe that's attached, or an additional device. In all cases, the idea is that the speech signal from the teacher is transmitted directly to the child wearing the hearing aid and receiver. And now they can hear and understand as effectively as possible.

Now my colleague Leigh Martin will show you how to verify an FM system and make sure that it's acting transparently. Afterwards, we will welcome back Lisa Bull, who will discuss using radio aids in the real world.

How to verify an FM system

Leigh Martin: Let's look at how we verify an FM system.

First of all, we need to measure the response of the hearing aid on its own. Therefore, we place the hearing aid in the test box as we normally would have it positioned and press OK. We will then present a 12 second ISTS signal to the instrument. And this will record the frequency response on the screen.

Once the test is finished, we're now ready to complete the second step. This is to switch the FM system on. Here, we still keep the hearing aid inside the test box. But we activate the FM system to see if there's any artifacts or noise coming into the system.

What we can do is come to the second stage of the protocol and run the response. Here we should expect to see an identical frequency response as we saw on the previous curve. And you can see after 12 seconds of ISTS signal, then the frequency response begins to match exactly what we were expecting to see.

The final step is to take the hearing aid outside of the test box and in its place, put the FM microphone inside. Here you want to align the microphone of the FM system with the reference microphone of the test box. This is the same way as you would with the hearing aid.

Once everything is in position, then the test box lid can be closed, and we can enter the software in order to measure the response. Inside we select the third step in the protocol FM mic plus hearing aid and push start.

This time a response curve colored in green will appear on screen. And again, we're looking for it to mimic the response of the hearing aid in order for it to be acoustically transparent. We can see that after 12 seconds of ISTS signal that this isn't the case, and therefore you need to go into the hearing aid fitting program or the FM program and adjust this in order to improve the response of the FM system.

Once those adjustments have been made, you can rerun the measurement and another green line will appear on screen. We can see that those adjustments have made some improvement, but there's still a little bit of high frequency response which is not matching the hearing aid response.

Therefore, once the measurement has stopped, you can increase the high frequency response in the hearing aid fitting software.

And then lastly, run the measurement one final time. Here, we can now start to see a much better fitting response to target. And therefore we can now say that these two devices are acoustically transparent.

Why perform a transparency measurement?

Lisa Bull: So we do transparency measurements, every time we set up a child with radio aid, because we want to be able to match the output of the child's radio aid system with their very carefully set up hearing aid output.

It has a massive impact on how much of the lesson that the child can access. So if the teacher is wearing the radio aid microphone or the transmitter effectively and in the right place and is managing it, well, then that child has good access to the teacher's voice and to the content of the lesson.

How to use radio aids correctly

Lisa Bull: Yeah, that's the biggest challenge, actually, that we have in terms of management of radio aid systems with mainstream classroom teachers. And, and particularly lower down in sort of early years settings, where the, the, the lessons are more sort of free flow and much, much less structured.

And so a teacher, we put a lot of emphasis on our training for these classroom teachers, because it's vital that they wear the microphone in the correct place.

So at hands breadth from their mouth, no lanyards, scarves, jewelry, hair off of the microphone, because anything, obviously, that's bumping on to the microphone is affecting what that child's hearing what that child is listening to, and holding up pieces of paper, even that banging on the microphone, it's very unpleasant for the for the child.

So we do a lot of training around that. And we've got some video clips that we show teachers of, you know, what a child hears if those things are not looked after. And then another big issue we have is the muting. And so the system that we use now is better because it has a flashing light when it's muted.

So it's much more visual. But prior to that, to that system, we used a slightly different transmitter didn't have a flashing light when it was muted. And if a teacher forgets to mute, the transmitter, goes off to talk to another teacher go to the staff room or to the loo, or even to talk to another child in the classroom. And they haven't muted their transmitter.

Obviously, the child that's wearing the receivers is hearing lots of speech and language that is completely inappropriate for them, because it's nothing to do with them.

Challenges that affect radio aid usage

Yes, definitely, particularly as children get older and into their sort of early and mid-teenage years, if a radio aid is not well managed by the classroom teacher, children, young people do start to reject the radio aid particularly, and often, often is because of the mismanagement of the system.

But sometimes it's because of the aesthetics of, you know, not wanting to hand over the transmitter not wanting to highlight themselves as different to the rest of the children or the rest of the young people in the class. So, you know, we have to manage that and think about that as well. But certainly, mismanagement of the radio aid systems is a huge challenge.

Use of radio aids outside the classroom

Yes, so it's different in different areas across the country. Actually, some local authorities and sensory support services don't allow their radios systems to go home, because the school very much has the responsibility for looking after it.

Where I am and in some other services, radio aids are allowed to go home, because we can see the benefit of using it in other settings outside of an educational setting. So for example, football training, brownies, learning to ride a bike, being in the car, the little children that are strapped into a car seat behind them.

So there are lots and lots of situations outside of the educational setting where we feel that radio aids are extremely valuable. So, so our radio aids do go home.

So it has, it is a challenge for sure. Because obviously, these systems are very expensive. And when the systems are in school, as I mentioned, the school has responsibility for them, which they signed for. So if any, any part any component of the radio aid is lost, the school have to pay for it to be replaced.

Now, obviously, going outside of school, that kind of throws up issues around equal opportunity of access. And, you know, parents signing for equipment that doesn't belong to them. But saying that they're going to be responsible for looking after it and for not having to pay for it if it gets lost.

So we've kind of wrestled with that over the years. And we have changed our policies as the years gone by. And our current situation is that preschool children, so children that are not in school, so the radio aid is only used at home, parents do not have to sign to take, they have to sign to take responsibility for looking after it.

But if it happens to get lost, they don't have to pay for it. And also with the new types of hearing aids with the fully integrated receivers in them now. That's also thrown up a few challenges for us because obviously, children are taking receivers home. Without, you know, not through choice.

They're in the hearing aid so they have to take them home. So again, we're not asking parents to sign for those pieces of equipment. And as a service, you know that we have, we've taken a couple of hits on that in terms of equipment has gone missing, and we've just had to swallow the cost unfortunately.

But generally, we don't have too many pieces of equipment going missing outside of school, inside of school. Equipment does go missing but as I say that's then down to the school.