It's quite clear when someone is deaf or close to being deaf, but it's not always obvious when people we know are ever so slightly hard of hearing.
In fact, as we get older most people will suffer some hearing loss, something which in technical terms is called "presbycusis."
Scientists tell us that it's not something we can prevent, it's just the natural wear and tear of ageing, although you can certainly protect yourself from damaging your ears such as doing things like staying away from really loud noises.
The thing is, though, there are certain frequencies most of us just can't hear, especially as we age.
The question now is: how many frequencies can you hear?
Listen to this, and then tell us your result in the comments.
We'll start with a very easy frequency that most people should be able to hear.
It's 8,000 Hertz.
Hertz is a unit of frequency, equal to one cycle per second.
It was named after a German physicist called Heinrich Rudolf Hertz.
He was the guy who conclusively proved radio waves exist.
8,000 HZ should be a cinch for you.
In fact, if you can't hear it, it means you certainly have a hearing problem.
Here we go, listen to this.
Did you get that?
We guess most of you did.
As we said, just about everyone should be able to pick up that frequency.
This next one, though, well, if you are getting on in years, say over 50 years old, you might struggle.
This is 12,000 HZ.
How about that?
We wonder if many of you listeners are over 50.
If you are, please tell us if you heard the sound.
We guess most of you youngsters got it.
Maybe some of you in noisy places didn't, so we should tell you to either use headphones for these tests or go to a very quiet place.
Ok, on to the next.
This one is hard for anyone over 40 to hear, and we guess some of you guys watching are that age or getting near there.
This is 15,000 Hz.
Did you hear that?
If you are indeed over 40 there is a good chance you didn't.
If you didn't and you are worried, we guess now is a good time to tell you why you didn't hear it.
In an article in the Scientific American about sound frequencies that some people can't hear, it was written that some companies have come up with an idea of how to keep teens from hanging out outside their stores by playing certain frequencies that only youngsters can hear.
This EEEEEEEEEEEEEEE sound drives them nuts, and so they don't loiter around for long.
The adults can't hear it, and so they don't mind being around the store.
So there's the answer, it's just hearing loss as we age, and that's why some people can't hear 12,000 HZ.
We are all born with a wide range of frequencies we can hear, but we lose some of those frequencies.
Some frequencies even kids can't hear, but they might drive a dog crazy or get on a cat's nerves.
By the way, while presbycusis is a kind of hearing loss in a way, it doesn't mean you are going deaf.
It's just a very natural process related to the ageing of cells.
The next one is 14,400 HZ.
We are going to guess that quite a few of you can't hear this because usually only people under 25 can hear it.
Have a listen.
Did you catch that frequency?
If so, you are likely under 25.
Ok, on to the next, and now it's going to get harder.
It's really one for the teens, because anyone over the age of 18 should not be able to hear this.
If you can and are over 18, you can count yourself as being a little bit special.
The frequency is 17,400 HZ.
Some of you are thinking that was easy, and that's because you haven't reached the ripe old age of 18 yet.
Now's the time to tell you something.
Let's say you can't hear that, but you know for fact lots of your friends can.
Well, a fun thing to do is download an app of frequencies and just bug people by playing one.
If you want to empty a room, this might be a way to do it.
You could also use a frequency as a ringtone and so when your phone is going off all the time and your parents don't like the noise, well, why not use a frequency they can't hear.
Ok, now we are going to give you one that we bet none of you can hear.
Well, we say none, but it is possible.
This is going to be 18,000 HZ.
It's a fact that the highest frequency that most humans can hear is 20,000, so some of you might be able to hear it.
Ok, here we go.
Did any of you get that?
If you did, be sure to tell us.
But don't go yet, because we may as well give you that maximum of 20,000 HZ and if any of you can get this one you are quite unique.
Here it is.
So who got the 20,000?
Don't worry if you didn't, because we weren't expecting you to.
As we said, some animals can hear much higher frequencies.
That's why when you blow a dog whistle your pooch goes wild and you don't hear a thing.
Dog whistles are usually somewhere in the 23,000 HZ to 54,000 HZ range.
Cats can hear even higher frequencies, right up to 64,000 HZ.
Dolphins and bats can hear higher frequencies, up to 100,000 HZ.
So, how did you do?
Did you just fall into the natural age range?
Did any of you hear that 20,000?
Tell us in the comments.
Also, be sure to check out our other video "These are the signs that you are going through puberty."
Thanks for watching, and as always, don't forget to like, share and subscribe.