0:00:02 > 0:00:04TWEETING BIRDS
0:00:05 > 0:00:07BUZZING BEES
0:00:19 > 0:00:21This is a familiar scene.
0:00:21 > 0:00:24It's the Somerset countryside on a calm day.
0:00:24 > 0:00:26And it sounds familiar.
0:00:26 > 0:00:27I can hear the birds singing,
0:00:27 > 0:00:30I can hear the wind rustling through the trees
0:00:30 > 0:00:32and I can hear the insects around me.
0:00:32 > 0:00:35This isn't just a landscape, it's a soundscape.
0:00:35 > 0:00:40A constant flood of sound waves washing over me from all directions.
0:00:47 > 0:00:53'No matter where we are or where we go, sound is always present.
0:00:55 > 0:01:01'And each individual noise offers us information about our world
0:01:01 > 0:01:04'from a moment in time and space.
0:01:04 > 0:01:08'Every sound wave carries a story about where it's come from
0:01:08 > 0:01:10'and the journey it's been on.'
0:01:10 > 0:01:13And our evolutionary history has given us these two detectors
0:01:13 > 0:01:16for tapping into those stories.
0:01:16 > 0:01:20What we hear shapes our understanding of our world.
0:01:24 > 0:01:27'In this programme, I'm going to explore how we exploit,
0:01:27 > 0:01:30'manipulate and control sound.'
0:01:32 > 0:01:36Just the quality of the sound says something's not right in here.
0:01:36 > 0:01:39'I'll delve into the complex ways in which our own bodies
0:01:39 > 0:01:44'precisely decode the information carried in sound waves.'
0:01:48 > 0:01:49That's amazing.
0:01:49 > 0:01:52When you take it off I can hear nothing.
0:01:52 > 0:01:54It's incredible!
0:01:57 > 0:02:00'And how the more we've come to understand sound,
0:02:00 > 0:02:03'the more we've been able to use it
0:02:03 > 0:02:06'to make remarkable discoveries about life...
0:02:07 > 0:02:09'..our planet...
0:02:11 > 0:02:13'..and even the solar system.'
0:02:29 > 0:02:34'In our normal everyday lives, it's hard to really appreciate
0:02:34 > 0:02:37'how much information sound carries.'
0:02:39 > 0:02:42- Want to put the helmet on?- OK. - You need those, as well.
0:02:42 > 0:02:46'Which is why acoustic engineer Professor Trevor Cox is taking me
0:02:46 > 0:02:51'to a hidden location deep inside the hills of Scotland.
0:02:57 > 0:03:02'Where, in the absence of light, hearing becomes my primary sense.'
0:03:07 > 0:03:10I'm going to go in first, so I shall demonstrate.
0:03:16 > 0:03:18It's ever so slightly sinister, this, isn't it?
0:03:18 > 0:03:21- There's your helmet.- OK. - You want to put your gloves on.
0:03:21 > 0:03:24I've probably have nightmares about doing something like this.
0:03:24 > 0:03:25Slide yourself in.
0:03:31 > 0:03:35Now, just be really careful as you get up. A bit further.
0:03:36 > 0:03:39- OK?- What have I arrived into?
0:03:39 > 0:03:41I'm going to be slightly cruel and turn my head torch off
0:03:41 > 0:03:43so we can't really see.
0:03:43 > 0:03:46We're just really working with the acoustic here.
0:03:46 > 0:03:48You have one of those. Shall we wander in just a bit further?
0:03:48 > 0:03:50Very, very dark, isn't it?
0:03:50 > 0:03:52- Watch where you walk. - Urgh, that's horrid.
0:03:52 > 0:03:55This is where the baddie turns up, right?
0:03:55 > 0:03:57Two people walk into a dark space
0:03:57 > 0:04:01and just the quality of the sound says something's not right here.
0:04:01 > 0:04:04'Just from the way that sounds behave in this place,
0:04:04 > 0:04:08'I'm beginning to piece together a picture of what it might be like.'
0:04:08 > 0:04:10What do you think this space is?
0:04:10 > 0:04:13So, it feels like it's gigantic.
0:04:13 > 0:04:16I can't tell because I can't see anything but it feels as though
0:04:16 > 0:04:19it could be enormous - the size of a cathedral or bigger.
0:04:19 > 0:04:22Just because that's the only place
0:04:22 > 0:04:26I've heard this sort of thing happen to my voice before.
0:04:27 > 0:04:30I'm finding it hard to finish a sentence because I keep saying
0:04:30 > 0:04:34a word and then stopping to listen to what it sounds like.
0:04:34 > 0:04:37When you listen to a sound in a room you can get a lot of information.
0:04:37 > 0:04:40You'll get the sound straight from me to you
0:04:40 > 0:04:43and then all the walls are contributing reflections -
0:04:43 > 0:04:45the sound's bouncing around the room.
0:04:45 > 0:04:48All the time in a space we're listening for these sort of clues.
0:04:48 > 0:04:51But we're not usually that, you know, conscious we're doing it.
0:04:51 > 0:04:55'The ability of sound to reflect is one of the most critical ways
0:04:55 > 0:04:58'it can carry information.
0:04:58 > 0:05:02'But sound reflections can tell me more than the size of a place.
0:05:02 > 0:05:05'I just need a different type of sound.'
0:05:05 > 0:05:07- I've got a stopwatch for you there. - OK.
0:05:07 > 0:05:10- So, if you could wait for... hear the bang.- Yeah.
0:05:10 > 0:05:14And then just measure how long it takes the sound to decay to nothing,
0:05:14 > 0:05:17which is actually how they first measured reverberation.
0:05:17 > 0:05:19- I shall retreat to a safe distance. - Yeah!
0:05:36 > 0:05:38I just dropped it.
0:05:39 > 0:05:41I can't see...
0:05:44 > 0:05:46LOUD BANG
0:05:47 > 0:05:50SOUND SLOWLY DIMINISHES
0:06:06 > 0:06:0857 seconds.
0:06:09 > 0:06:11Wow.
0:06:11 > 0:06:13This place actually holds the world record
0:06:13 > 0:06:15for the longest reverberation time,
0:06:15 > 0:06:18which is what you kind of measured there.
0:06:18 > 0:06:20What's going on to make that happen?
0:06:20 > 0:06:22First of all, it's a very big place.
0:06:22 > 0:06:24But there must be something more than that
0:06:24 > 0:06:26because if you go into St Paul's Cathedral in London,
0:06:26 > 0:06:29the sound would only last about ten seconds before dying away.
0:06:29 > 0:06:33The sound is being contained and held in this giant space.
0:06:33 > 0:06:36And that's because the walls here are incredibly massive.
0:06:36 > 0:06:39You can tell that this must have hard, heavy walls,
0:06:39 > 0:06:42whereas if you brought a lot of soft furnishings in,
0:06:42 > 0:06:44which absorb sound, this place would go dead.
0:06:44 > 0:06:46So, we're getting extra information
0:06:46 > 0:06:49because sound reflects differently off different materials.
0:06:49 > 0:06:51What is this place? After all that, where are we?
0:06:51 > 0:06:53Well, let's put the lights on.
0:07:06 > 0:07:07So, this is a massive space.
0:07:07 > 0:07:09It's about a quarter of a kilometre long
0:07:09 > 0:07:12so that's where a lot of the reverberations come.
0:07:12 > 0:07:15- What's it doing here?- Well, it's actually an oil storage depot
0:07:15 > 0:07:17which was built in the run-up to World War II
0:07:17 > 0:07:20to protect the Royal Navy shipping oil from bombing.
0:07:20 > 0:07:22So, it's been made bombproof
0:07:22 > 0:07:25and that's the reason it's got this huge reverberance.
0:07:25 > 0:07:27They've made it out of half-metre-thick concrete
0:07:27 > 0:07:30and behind it is the bedrock of Scotland.
0:07:30 > 0:07:32So, this is really massive walls.
0:07:32 > 0:07:34And the walls are covered in oil, as well. It's horribly sticky.
0:07:34 > 0:07:37Sticky on your feet, everywhere. That's really useful acoustically.
0:07:37 > 0:07:40Concrete's a bit porous so normally you get a little bit of absorption
0:07:40 > 0:07:43but its pores have been gunked up with oil.
0:07:43 > 0:07:46So, what's happening is that the sound is reflecting off the walls
0:07:46 > 0:07:48really efficiently, it's not getting absorbed.
0:07:48 > 0:07:51You can get a tremendous lot of information by looking at
0:07:51 > 0:07:54the pattern of reflections, and, as an acoustic engineer,
0:07:54 > 0:07:57that's what you do when you design a grand concert hall.
0:07:59 > 0:08:02SAXOPHONE REVERBERATES
0:08:08 > 0:08:10You try and design the pattern of reflections
0:08:10 > 0:08:13to be just right to enhance the music.
0:08:14 > 0:08:16SAXOPHONE REVERBERATES
0:08:34 > 0:08:37'The reason that sound can carry so much information
0:08:37 > 0:08:41'is because of its fundamental nature.
0:08:41 > 0:08:43'It travels as a wave.
0:08:44 > 0:08:47'And every time a sound wave reflects off a surface
0:08:47 > 0:08:50'it's changed in subtle ways.'
0:08:52 > 0:08:54Reflection is a way of redirecting sound
0:08:54 > 0:08:57and that redirected sound carries information
0:08:57 > 0:09:00about the obstacle it bounced off.
0:09:00 > 0:09:04We use that acoustic signature to learn about our environment
0:09:04 > 0:09:07in a general way, but there are animals that absolutely rely on it,
0:09:07 > 0:09:10and they are the true masters of sound.
0:09:31 > 0:09:35'For most bats, hearing is their primary sense.
0:09:35 > 0:09:39'Listening to sound reflections is key to their survival.
0:09:42 > 0:09:45'And their success has driven complex relationships
0:09:45 > 0:09:50'with other creatures that live in and exploit this auditory world.
0:09:54 > 0:09:58'Bats are one of the loudest creatures in the animal kingdom.
0:09:58 > 0:10:01'We can't hear them because they mostly use frequencies
0:10:01 > 0:10:05'our ears can't detect, making it quite difficult for bat experts
0:10:05 > 0:10:08'like Dr Marc Holderied to study them.'
0:10:08 > 0:10:11We have an acoustic camera that can pick up ultrasound
0:10:11 > 0:10:14and we've just put it in one of my favourite research spots.
0:10:14 > 0:10:15So, this is a commuting corridor
0:10:15 > 0:10:17with loads of bats using it every night.
0:10:17 > 0:10:21And this acoustic camera now shows me what is going on
0:10:21 > 0:10:23as we look at this screen.
0:10:23 > 0:10:26We've just seen two bats flying and there's a third one.
0:10:26 > 0:10:28So, there's a whole group flying past.
0:10:28 > 0:10:31You can see all these whitish yellowish blobs there.
0:10:31 > 0:10:33As the bat was flying past
0:10:33 > 0:10:35it was emitting these ultrasonic frequencies.
0:10:35 > 0:10:37So, you're looking for patterns?
0:10:37 > 0:10:40We can look at this spectrogram display down here
0:10:40 > 0:10:43and try and find out which species we were looking at.
0:10:43 > 0:10:45There's another one coming right now.
0:10:45 > 0:10:49Now, if you look at that, they all ended about the same frequency.
0:10:49 > 0:10:50They're around 45 kilohertz,
0:10:50 > 0:10:53which tells us that this is a common pipistrelle.
0:10:53 > 0:10:56And just now is a very different call.
0:10:56 > 0:10:58And I can tell you that this is a Daubenton's bat.
0:10:58 > 0:11:01So, you're painting this picture of all these bats whooshing past us,
0:11:01 > 0:11:03making sounds that we can't hear.
0:11:03 > 0:11:06If we could hear them, what would we hear?
0:11:06 > 0:11:08What I've brought along here is a tiny bat detector.
0:11:08 > 0:11:12It turns the ultrasonic frequencies into audible frequencies.
0:11:12 > 0:11:15- That was a bat! - There's one flying over right now.
0:11:15 > 0:11:18We heard this very quick succession of calls there.
0:11:18 > 0:11:21There it is again. Very good. It just whizzed over there.
0:11:21 > 0:11:24So, they're very short and sharp and even though that sounds very quick
0:11:24 > 0:11:27- to us, there's a lot going on between one pulse and the next.- Yes.
0:11:28 > 0:11:31They send out the high-intensity sound...
0:11:32 > 0:11:35..and then they hit all the obstacles that are in the area.
0:11:35 > 0:11:37These obstacles produce echoes
0:11:37 > 0:11:40and the bat then waits for these to come back.
0:11:42 > 0:11:45The further away an object is, the longer the echo takes to return
0:11:45 > 0:11:48to the bat and this is how bats measure distance.
0:11:49 > 0:11:53And that is an incredibly complex achievement.
0:11:54 > 0:11:56There is so many different reflectors, like all the leaves,
0:11:56 > 0:11:59you have the ground, you have all the branches,
0:11:59 > 0:12:01and all of them produce echoes.
0:12:10 > 0:12:14'Bats evolved the ability to use sound to see
0:12:14 > 0:12:17'at least 53 million years ago...
0:12:18 > 0:12:21'..giving them an enormous advantage when hunting for prey
0:12:21 > 0:12:23'under the cover of darkness.'
0:12:25 > 0:12:28So, we've got a moth here. What species is it?
0:12:28 > 0:12:29It's a heart and dart.
0:12:29 > 0:12:31It's got this beautiful gold sheen.
0:12:31 > 0:12:34Yeah, yeah, yeah, they are quite beautiful.
0:12:34 > 0:12:36And how's a bat going to find this moth?
0:12:36 > 0:12:41So, a bat uses biosonar not only for navigation but also to capture prey.
0:12:41 > 0:12:45So, when they are searching for insects, they want to look very far.
0:12:45 > 0:12:49So, what they use is their lowest frequency calls that carry very far.
0:12:49 > 0:12:51But as soon as they've detected the moth,
0:12:51 > 0:12:54they add in higher frequencies to their calls.
0:12:54 > 0:12:56BAT CALLS
0:12:56 > 0:12:59Higher frequencies have shorter wavelength
0:12:59 > 0:13:01and give them better resolution.
0:13:01 > 0:13:05And better resolution means they can localise the moth very well.
0:13:05 > 0:13:07BAT CALLS
0:13:09 > 0:13:11And the bat sonar is giving it a brilliant tool
0:13:11 > 0:13:14for finding these very fast-moving moths.
0:13:14 > 0:13:16Do they have it all their own way?
0:13:16 > 0:13:18Moths, of course, are fighting back.
0:13:18 > 0:13:22All these moths had to do is evolve an ultrasound sensitive ear
0:13:22 > 0:13:25that picks up the frequencies the bats emit, and they did.
0:13:25 > 0:13:28- So, can this moth hear? - This moth has ears, yes.
0:13:28 > 0:13:30When they hear a bat that's far away,
0:13:30 > 0:13:32they just steer out of harm's way.
0:13:32 > 0:13:35And so, there's, sort of, one of these arms races going on
0:13:35 > 0:13:39where one species makes a change that makes them more successful
0:13:39 > 0:13:41and then their prey species also has to adapt.
0:13:41 > 0:13:44So... Oh, it's going for a walk again.
0:13:44 > 0:13:46And are there any other strategies that a moth could take
0:13:46 > 0:13:49- to avoid this bat that's coming to get it for dinner?- Yes.
0:13:49 > 0:13:51Moths have taken the next step.
0:13:51 > 0:13:55Moths have evolved a jamming mechanism
0:13:55 > 0:13:59that helps them throw the biosonar off target.
0:14:00 > 0:14:02You have a moth that knows it's under attack,
0:14:02 > 0:14:05it produces ultrasonic clicks.
0:14:05 > 0:14:08And these ultrasonic clicks are in the similar frequency range
0:14:08 > 0:14:11as the echoes a bat is expecting.
0:14:11 > 0:14:14But if it hears these clicks rather than the echoes
0:14:14 > 0:14:18it can't really make out a full echolocation picture any more.
0:14:19 > 0:14:23And that gives the moth the time to just whizz out of the way.
0:14:23 > 0:14:25MOTH CLICKS
0:14:31 > 0:14:35'This sophisticated interplay between bats and moths
0:14:35 > 0:14:38'shows just how rich in information
0:14:38 > 0:14:42'and how valuable reflecting sound waves can be.
0:14:42 > 0:14:46'But reflections are not the only way sound waves help us
0:14:46 > 0:14:48'understand our surroundings.
0:14:48 > 0:14:51'There's another feature of sound that can provide us with
0:14:51 > 0:14:54'even more information about the world.
0:14:54 > 0:14:58'And it's particularly useful in warning us of approaching danger.
0:15:00 > 0:15:02CAR HORN
0:15:05 > 0:15:07AMBULANCE SIREN
0:15:10 > 0:15:12LOUD TRAFFIC NOISES
0:15:16 > 0:15:19I live in London and I cycle all the time
0:15:19 > 0:15:23and it's easily the most dangerous thing I do on a daily basis.
0:15:23 > 0:15:25There's so much traffic here.
0:15:26 > 0:15:30Vans like that that overtake you when you're not expecting them.
0:15:32 > 0:15:35What I'm conscious of is paying attention to light.
0:15:35 > 0:15:38I can see what's in front of me, I look behind me,
0:15:38 > 0:15:40that makes me feel secure.
0:15:40 > 0:15:43But I'm getting a lot of extra information from sound.
0:15:48 > 0:15:50Two things that really worry me when I'm cycling,
0:15:50 > 0:15:52and they are big trucks and motorcycles.
0:15:52 > 0:15:55Fortunately, both of them make a huge amount of noise.
0:15:55 > 0:15:57That was a motorbike.
0:15:57 > 0:16:00And you can hear them coming, even from around the corner.
0:16:00 > 0:16:02LOUD MOTORCYCLE ENGINE
0:16:02 > 0:16:04I certainly heard him.
0:16:06 > 0:16:09'We can often hear things we can't see
0:16:09 > 0:16:13'because, unlike light, sound can travel around corners.
0:16:18 > 0:16:21'It's something made possible when a fundamental feature
0:16:21 > 0:16:25'of the sound wave is just right - its size.'
0:16:25 > 0:16:27It works a bit like this.
0:16:27 > 0:16:29If we imagine we've got an obstacle in the way
0:16:29 > 0:16:32and in this case that could be the corner of a building.
0:16:32 > 0:16:35I'm going to draw a sound source over here.
0:16:35 > 0:16:39Sound is spreading out in ripples, like the ripples on a pond.
0:16:39 > 0:16:42So, as the sound travels away, those ripples spread out.
0:16:42 > 0:16:44They can spread around the corner.
0:16:44 > 0:16:48So, if I was standing here, I might not be able to see the sound source
0:16:48 > 0:16:50but I would be able to hear the sound.
0:16:50 > 0:16:52And this is called diffraction.
0:16:52 > 0:16:55It doesn't work in the same way for all wavelengths
0:16:55 > 0:16:58because diffraction depends on how the wavelength
0:16:58 > 0:17:00is related to the size of the obstacle.
0:17:00 > 0:17:02And a corner of a building is quite big.
0:17:02 > 0:17:06So, this time I'm going to draw a higher frequency sound
0:17:06 > 0:17:09which means the wavelengths are much shorter.
0:17:09 > 0:17:13So, they'll spread out like ripples and they will diffract a little bit
0:17:13 > 0:17:17as they go around the corner but not nearly as much.
0:17:17 > 0:17:20So, sound that might be a wavelength of a few centimetres
0:17:20 > 0:17:22are much smaller than the corner of the building
0:17:22 > 0:17:25so I can't hear the high frequencies here
0:17:25 > 0:17:27but I can hear the low frequencies.
0:17:31 > 0:17:33'Most sounds can travel around objects
0:17:33 > 0:17:36'because their wavelength is relatively big.
0:17:37 > 0:17:40'Light, on the other hand, has a very short wavelength.
0:17:43 > 0:17:45'Which means there are very few things in our world
0:17:45 > 0:17:47'that it can bend around.
0:17:47 > 0:17:51'Instead, light stops and casts a shadow.
0:17:59 > 0:18:03'The ease with which sound can travel around the environment
0:18:03 > 0:18:07'has played an important role in the story of our survival.
0:18:08 > 0:18:11'Because it means we can hear the roar of a hungry lion
0:18:11 > 0:18:15'or the rumble of a truck - even if we can't see them.'
0:18:15 > 0:18:18The diffraction of sound does more than just let me know
0:18:18 > 0:18:21that there's a sound source somewhere near me.
0:18:21 > 0:18:25It helps me pinpoint exactly where that sound source is.
0:18:33 > 0:18:36'This ability is called localisation.
0:18:38 > 0:18:42'Every animal needs to know which direction danger is coming from.
0:18:43 > 0:18:47'It works because sound doesn't just diffract around our environment,
0:18:47 > 0:18:50'but also around the listener.
0:18:55 > 0:18:59'Dr Jenny Bizley is here to show me the complex mechanisms
0:18:59 > 0:19:01'we use to localise sound.'
0:19:01 > 0:19:04So, I don't know where the sound's going to come from?
0:19:04 > 0:19:07No, so if you face the front, I'll play a sound
0:19:07 > 0:19:11and then you can maybe point to where you think it comes from.
0:19:11 > 0:19:12No pressure!
0:19:13 > 0:19:16LOUD MONKEY CHATTER Oh, it's loud, isn't it?
0:19:16 > 0:19:18- Somewhere over there. - Yeah, that's right.
0:19:18 > 0:19:20We'll try another one.
0:19:20 > 0:19:23GRUNTING Up there!
0:19:24 > 0:19:26Yeah. And how about this one?
0:19:26 > 0:19:29LOUD WHOOSHING Somewhere up there.
0:19:29 > 0:19:32CRASHING Something broke over there.
0:19:32 > 0:19:34'Although I'm not conscious of it,
0:19:34 > 0:19:38'my brain is precisely locating each sound I'm hearing.'
0:19:38 > 0:19:40So, the biggest bee in the world is over there!
0:19:40 > 0:19:42Oh, it's moving.
0:19:42 > 0:19:45'And it's not limited to fixed sounds.
0:19:48 > 0:19:51'To understand how we localise sound,
0:19:51 > 0:19:55'we need to look at the way it moves around our bodies
0:19:55 > 0:19:59'and interacts with the two ears on opposite sides of our head.'
0:20:00 > 0:20:02So, we're going to play the sound of the twig snapping
0:20:02 > 0:20:05that you heard previously from one of the speakers over there,
0:20:05 > 0:20:07and it was coming from the left of the head.
0:20:07 > 0:20:09And we'll look at the input from the microphones on here.
0:20:09 > 0:20:12So, we should see the sound waves coming in here.
0:20:12 > 0:20:13TWIG SNAPPING
0:20:13 > 0:20:16So, this is the signal from the first microphone,
0:20:16 > 0:20:17which is on the left,
0:20:17 > 0:20:19and this is the signal from the right microphone.
0:20:20 > 0:20:22- And they look very different. - Yes.
0:20:22 > 0:20:25You can see that the left-hand microphone is picking up a signal
0:20:25 > 0:20:28that's much louder than the signal on the right.
0:20:28 > 0:20:29And it's also arriving sooner.
0:20:29 > 0:20:32The timing difference, how long is that from there to there?
0:20:32 > 0:20:36From there to there is about 500 microseconds.
0:20:36 > 0:20:38So, just about half of a millisecond.
0:20:38 > 0:20:39So, the sound reached my left ear
0:20:39 > 0:20:42- half a millisecond before it reached my right ear?- Yeah.
0:20:42 > 0:20:43We can measure that difference
0:20:43 > 0:20:46because sound moves relatively slowly, at least compared to light.
0:20:46 > 0:20:50The difference in timing is useful for low-frequency sounds.
0:20:50 > 0:20:53Because the low-frequency sound has quite a long wavelength,
0:20:53 > 0:20:55longer than the width of the head,
0:20:55 > 0:20:58the sound can diffract around the head to the far ear,
0:20:58 > 0:20:59but it does so with a delay.
0:20:59 > 0:21:03The other big difference here is the amplitude - the level of the sound.
0:21:03 > 0:21:06What's the level difference between one ear and the other?
0:21:06 > 0:21:09For this sound, we have a difference of the order of a few decibels,
0:21:09 > 0:21:125-10, depending on the frequency of the sound.
0:21:12 > 0:21:15- So, that's quite a lot, is it? - That's quite a large difference.
0:21:15 > 0:21:17The amplitude difference is important really
0:21:17 > 0:21:20for high-frequency sounds which have shorter wavelengths.
0:21:20 > 0:21:23They are not able to diffract around the head
0:21:23 > 0:21:25and they are shadowed by the head.
0:21:25 > 0:21:28So, the signal will be louder in the near ear and quieter in the far ear.
0:21:28 > 0:21:31These signals are kept within the brain and they're kept separately
0:21:31 > 0:21:34until higher up, sort of, in the processing hierarchy,
0:21:34 > 0:21:37when they're put together to give you a perception of space.
0:21:37 > 0:21:40And that means that, within seconds, you can tell where a sound
0:21:40 > 0:21:43comes from so that you can avoid it if it's going to eat you, or...
0:21:43 > 0:21:45I definitely avoid sounds that are going to eat me!
0:21:49 > 0:21:53'However, this system only works for localising sound
0:21:53 > 0:21:55'in the horizontal plane.
0:21:58 > 0:22:02'To know whether the sound is coming from above or below,
0:22:02 > 0:22:06'we use a trick that depends on the shape of each individual ear.
0:22:13 > 0:22:17'To show me, Jenny has kindly brought with her what looks like
0:22:17 > 0:22:19'an awful lot of Blu-Tack.'
0:22:19 > 0:22:21You know at school,
0:22:21 > 0:22:24teachers were always taking Blu-Tack out of people's ears.
0:22:24 > 0:22:26Somehow, you get older, and you become a scientist
0:22:26 > 0:22:28and it works the other way around.
0:22:28 > 0:22:32'The aim is to smooth out the folds of my outer ear.'
0:22:32 > 0:22:34There you are. Take your finger out.
0:22:34 > 0:22:37OK, now I've got ears full of Plasticine. Brilliant!
0:22:37 > 0:22:41Sound can still go down there but it can't bounce off all of this.
0:22:41 > 0:22:43I'm going to clap somewhere in front of you
0:22:43 > 0:22:46and you should just close your eyes and then point at it.
0:22:46 > 0:22:47OK, all right.
0:22:48 > 0:22:50Erm, there?
0:22:51 > 0:22:52No?!
0:22:52 > 0:22:55OK, give me another try, give me another try. Go on.
0:22:56 > 0:22:58- Down there?- No.
0:22:59 > 0:23:01There?
0:23:01 > 0:23:03So, I'm rubbish at this with these in my ears.
0:23:03 > 0:23:06I'm going to take these out because they're doing...
0:23:06 > 0:23:08It does make the world sound very weird, actually.
0:23:08 > 0:23:12When I've got them in, it's like there's less going on
0:23:12 > 0:23:14and I take them out and suddenly the world opens out.
0:23:14 > 0:23:17You're just missing that information that you're used to having.
0:23:17 > 0:23:21'Ordinarily, sound waves will interact with my outer ear
0:23:21 > 0:23:23'before travelling inside.'
0:23:23 > 0:23:25When I clap, I make a broadband sound,
0:23:25 > 0:23:27so it has many sound frequencies in it.
0:23:27 > 0:23:30As the sound comes in, depending on where it comes from,
0:23:30 > 0:23:32it'll hit different parts of your ear.
0:23:32 > 0:23:34As it hits these complicated folds,
0:23:34 > 0:23:38some sound frequencies are made louder and others are made quieter,
0:23:38 > 0:23:41and your brain's learned over time how to interpret these changes
0:23:41 > 0:23:44that occur, according to where the sound comes from.
0:23:44 > 0:23:47You're listening for really subtle changes in the frequency composition
0:23:47 > 0:23:49of the sound that are introduced by
0:23:49 > 0:23:51the folded structure of the outer ear.
0:23:51 > 0:23:55So, the ear here is not just guiding sound in, this outer bit,
0:23:55 > 0:23:57it's actually changing it.
0:23:57 > 0:23:59So, it's really clever. That's really complicated
0:23:59 > 0:24:01and really clever at the same time.
0:24:01 > 0:24:03It is really clever and you have to learn to do it.
0:24:03 > 0:24:05Everyone's ears are different
0:24:05 > 0:24:08and the peculiarities of your outer ear are special to you.
0:24:10 > 0:24:14'The properties of sound waves and the way they travel
0:24:14 > 0:24:17'carry important messages about our environment.
0:24:22 > 0:24:26'But once those messages enter our ears, they need to be translated.'
0:24:32 > 0:24:35In order to access this information that's all around us,
0:24:35 > 0:24:37we need a detector.
0:24:37 > 0:24:40Something that can convert these tiny vibrations of the air
0:24:40 > 0:24:43into a signal our brain can understand.
0:24:44 > 0:24:47'Most of us take hearing for granted,
0:24:47 > 0:24:51'because it happens apparently automatically deep inside our ears.'
0:24:52 > 0:24:55The reason that we can hear so much and so well
0:24:55 > 0:24:58is that our ears are sophisticated detectors -
0:24:58 > 0:25:02a series of different structures all working together.
0:25:02 > 0:25:05If just one of the links in that chain is broken
0:25:05 > 0:25:07the consequences can be devastating.
0:25:15 > 0:25:17'I miss not hearing the birds.
0:25:20 > 0:25:24'I lost my hearing very, very quickly.
0:25:24 > 0:25:26'You can't believe it's happening.
0:25:29 > 0:25:32'You think, "Oh, did I hear something?"
0:25:33 > 0:25:35'But, no, you don't.
0:25:39 > 0:25:42'It really is frightening.'
0:25:49 > 0:25:51'This is Barbara.
0:25:51 > 0:25:54'She lives with her husband, Tony,
0:25:54 > 0:25:57'and they've been married for 53 years.'
0:25:57 > 0:25:59LAUGHTER
0:25:59 > 0:26:01- What's funny?- Hm?
0:26:01 > 0:26:02What's funny?
0:26:02 > 0:26:05'But, for the past year and a half,
0:26:05 > 0:26:07'they've not been able to communicate properly.'
0:26:07 > 0:26:10Crashed on...the wires...!
0:26:12 > 0:26:16'Because, very suddenly, Barbara became profoundly deaf.'
0:26:18 > 0:26:21'I can't hear anything round out here.
0:26:21 > 0:26:25'I just miss my old life in general, really.
0:26:25 > 0:26:26'Yeah.'
0:26:26 > 0:26:30Not, sort of, hearing people or knowing what they're talking about.
0:26:30 > 0:26:32That's quite difficult.
0:26:32 > 0:26:35Deafness is a lonely world.
0:26:36 > 0:26:41'Barbara lost her hearing because just one small part of her ear
0:26:41 > 0:26:43'stopped working.
0:26:51 > 0:26:55'When sound enters a healthy ear, it gets funnelled through
0:26:55 > 0:26:58'to a coiled up structure called the cochlea -
0:26:58 > 0:27:04'a spiral-shaped cavity containing some 16,000 specialised cells
0:27:04 > 0:27:06'called hair cells.
0:27:07 > 0:27:10'As the sound wave moves through the cochlea,
0:27:10 > 0:27:13'the cells' hairlike protrusions are displaced...
0:27:15 > 0:27:18'..causing the cell to send electrical impulses
0:27:18 > 0:27:22'along nerve fibres that are destined for the brain.
0:27:26 > 0:27:30'But Barbara's hair cells are no longer working,
0:27:30 > 0:27:33'which means that although the rest of her ear is healthy,
0:27:33 > 0:27:37'her brain is completely starved of sound.'
0:27:39 > 0:27:41'I miss my independence.'
0:27:43 > 0:27:48What I try not to do is get down. I try to think positive.
0:27:51 > 0:27:54How are you feeling about today?
0:27:54 > 0:27:56- I'm OK. Yeah.- OK?
0:27:56 > 0:27:58How about you?
0:27:58 > 0:28:01Bit nervous, I suppose.
0:28:01 > 0:28:05'A month ago, Barbara was fitted with a cochlear implant.
0:28:05 > 0:28:09'An array of electrodes has been threaded into her cochlea
0:28:09 > 0:28:12'that will take over the role of her faulty hair cells.
0:28:12 > 0:28:15'And today, at Southampton University,
0:28:15 > 0:28:18'it will be switched on and tested for the first time.
0:28:18 > 0:28:21So, I'm going to switch it on, OK?
0:28:25 > 0:28:27- Can you hear anything? - Not yet, no.
0:28:27 > 0:28:29Just going to bring it up.
0:28:30 > 0:28:31Nothing.
0:28:39 > 0:28:41BEEPING
0:28:41 > 0:28:43Very faint.
0:28:43 > 0:28:45Very, very faint.
0:28:45 > 0:28:46BEEPING
0:28:46 > 0:28:49Very gradual, isn't it?
0:28:49 > 0:28:50Yeah. Bit more?
0:28:50 > 0:28:52Yes.
0:28:52 > 0:28:55I'm going to keep talking as I bring it up, OK?
0:28:55 > 0:28:57Just going to keep bringing it up.
0:28:57 > 0:28:59How did you get here today, Tony?
0:28:59 > 0:29:01I can hear... Can't understand.
0:29:01 > 0:29:04I can almost hear my own voice again!
0:29:06 > 0:29:08How's the volume now?
0:29:08 > 0:29:11How's the volume?
0:29:11 > 0:29:13- Yes!- The volume?
0:29:13 > 0:29:17- The volume. How's the volume now, you said, yes.- Yeah.
0:29:17 > 0:29:19What can you hear?
0:29:19 > 0:29:22- Can you hear me? - Yes, I can hear you.
0:29:22 > 0:29:23Oh, dear.
0:29:23 > 0:29:26No, it's good.
0:29:26 > 0:29:28Yeah.
0:29:29 > 0:29:31'For the first time in over a year,
0:29:31 > 0:29:35'Barbara's brain is receiving sound signals.'
0:29:35 > 0:29:37- OK?- That's amazing.
0:29:37 > 0:29:40When you take it off I can hear nothing.
0:29:42 > 0:29:43Amazing, yes.
0:29:43 > 0:29:45Don't make me cry!
0:29:48 > 0:29:50Don't worry about a hanky.
0:29:51 > 0:29:54- So, you're noticing the difference? - It's incredible.
0:29:55 > 0:29:58Stop it. You're going to make me cry.
0:29:58 > 0:30:00Thank you.
0:30:01 > 0:30:03Oh, dear.
0:30:03 > 0:30:05I didn't think it would be this quick.
0:30:05 > 0:30:07No, you're doing really well.
0:30:07 > 0:30:10I thought for my birthday in July I might be able to hear then.
0:30:11 > 0:30:15What are we going to have for dinner tonight, some champagne?
0:30:15 > 0:30:18Stop it. You'll make me cry again!
0:30:26 > 0:30:29'Barbara is no longer lost in silence.
0:30:32 > 0:30:35'By translating sound into electrical signals,
0:30:35 > 0:30:39'the implant replicates the cochlea's key job,
0:30:39 > 0:30:43'returning Barbara to a world full of sound.
0:30:49 > 0:30:52'The cochlea is a truly extraordinary structure,
0:30:52 > 0:30:56'doing much more than simply translating noise.
0:30:56 > 0:31:00'It's also able to discriminate the incredible variation of sounds
0:31:00 > 0:31:02'in our environment.'
0:31:02 > 0:31:05Even though it's quite quiet and calm where I am now, there's still
0:31:05 > 0:31:08a huge richness of information in the sound around me.
0:31:08 > 0:31:12And a lot of that richness comes in the frequency of the sound,
0:31:12 > 0:31:16the number of times every second that air molecules are vibrating
0:31:16 > 0:31:17backwards and forwards.
0:31:17 > 0:31:20It could be a hundred times or a thousand times
0:31:20 > 0:31:23and they're all overlaid on top of each other.
0:31:23 > 0:31:25So, the singing birds and the distant road
0:31:25 > 0:31:27are all creating an environment
0:31:27 > 0:31:29that's full of different frequencies
0:31:29 > 0:31:31and that is really useful information.
0:31:40 > 0:31:43'Our cochlea has a really clever way of telling us
0:31:43 > 0:31:46'which frequencies are coming into the ear.
0:31:48 > 0:31:51'It exploits a phenomenon called resonance
0:31:51 > 0:31:54'which can be demonstrated with these conkers.'
0:31:55 > 0:31:59You can see if I push on one and I push on another one,
0:31:59 > 0:32:03this one with the short string is going backwards and forwards
0:32:03 > 0:32:04really quite quickly.
0:32:04 > 0:32:07Whereas this one down here with a longer string,
0:32:07 > 0:32:11you can see it swings much, much more slowly.
0:32:11 > 0:32:14Each one has its own natural frequency.
0:32:14 > 0:32:16And it's different for every conker
0:32:16 > 0:32:18because the string is a different length.
0:32:18 > 0:32:22Now, the clever bit comes when a frequency comes from somewhere else.
0:32:22 > 0:32:24And I'm going to demonstrate that here with this apple.
0:32:24 > 0:32:27If I swing the apple, what happens is that the apple
0:32:27 > 0:32:31will gently move the string and that's forcing all the conkers
0:32:31 > 0:32:35to oscillate at the same frequency as the apple,
0:32:35 > 0:32:37however longer their string is.
0:32:37 > 0:32:40And you can see that these ones are moving a little bit,
0:32:40 > 0:32:42moving a little bit, little bit more, and this one,
0:32:42 > 0:32:45this one is the one that's really responding.
0:32:45 > 0:32:49And if you look at it from this angle, you can see that this conker
0:32:49 > 0:32:52is the one that's got the same length of string as the apple.
0:32:52 > 0:32:55The others are hardly moving at all and this one is swinging loads.
0:32:55 > 0:32:57'And I can show you what happens
0:32:57 > 0:33:00'when I change the frequency of the driving force.
0:33:01 > 0:33:05'By shortening the string, I can make the apple swing faster.'
0:33:06 > 0:33:09We can see that this time it's this one.
0:33:09 > 0:33:12This conker is responding really, really strongly
0:33:12 > 0:33:15and this is the one again that's got more or less
0:33:15 > 0:33:17the same length of string as the apple.
0:33:17 > 0:33:21It's got the same natural frequency as the oscillation coming in.
0:33:22 > 0:33:25And now it's trying to hit me in the face!
0:33:26 > 0:33:29This is the phenomenon of resonance.
0:33:29 > 0:33:32This is very similar to what's happening in the cochlea.
0:33:36 > 0:33:40'Just as the conker strings have a variety of natural frequencies,
0:33:40 > 0:33:43'so do structures in the ear.
0:33:46 > 0:33:50'The thousands of tiny hair cells that send messages to the brain
0:33:50 > 0:33:54'sit along a structure called the basilar membrane.
0:33:54 > 0:33:57'This stretched piece of elastic that runs through the cochlea
0:33:57 > 0:34:01'has different natural frequencies as you go along it.
0:34:01 > 0:34:04It's got one end which is narrow and taut
0:34:04 > 0:34:07and it's got a very high natural frequency of oscillation
0:34:07 > 0:34:11and the other end of the basilar membrane is wider and less taut
0:34:11 > 0:34:13and that's got a lower frequency of oscillation.
0:34:14 > 0:34:17So, when sound comes into our ear,
0:34:17 > 0:34:20the whole basilar membrane will vibrate a little bit
0:34:20 > 0:34:23but one part of it will really start to vibrate.
0:34:23 > 0:34:27The one that matches the frequency of the sound coming in.
0:34:28 > 0:34:32And it's the hair cells at that part of the basilar membrane
0:34:32 > 0:34:36that are stimulated, that send the sound into our brains
0:34:36 > 0:34:40and that's how our ears tell us which frequencies of sound
0:34:40 > 0:34:42are coming in from the environment around us.
0:34:45 > 0:34:50'This elegant and simple mechanism gives us the ability to detect
0:34:50 > 0:34:54'and interpret an enormous range of frequencies.
0:34:54 > 0:34:58'A far greater range of sounds than the spectrum of light waves
0:34:58 > 0:35:00'we can see with our eyes.
0:35:04 > 0:35:09'From low-sounding noises that go through 20 cycles a second
0:35:09 > 0:35:13'and have wavelengths 17 metres long.
0:35:17 > 0:35:20'All the way through to very high-frequency sounds
0:35:20 > 0:35:24'that can exceed 18,000 cycles a second
0:35:24 > 0:35:28'and have a wavelength of under two centimetres.
0:35:31 > 0:35:34'The cochlea's a sophisticated structure
0:35:34 > 0:35:37'that lets us detect a huge variety of sounds.
0:35:37 > 0:35:40This story is interesting because it passed through
0:35:40 > 0:35:45one of the most significant stages in evolutionary history.
0:35:45 > 0:35:50When hearing and life first evolved, it all happened underwater.
0:35:51 > 0:35:55'Which would mean that, one day, it would have to confront and overcome
0:35:55 > 0:35:57'a physical law of nature.
0:36:02 > 0:36:07'3.5 billion years ago, life began in the oceans.
0:36:10 > 0:36:13'And as organisms became ever more complex,
0:36:13 > 0:36:17'they developed increasingly sophisticated senses.
0:36:22 > 0:36:25'Around 400 million years ago,
0:36:25 > 0:36:28'fish became the first hearing animal,
0:36:28 > 0:36:30'evolving structures that,
0:36:30 > 0:36:33'although much simpler than the modern cochlea,
0:36:33 > 0:36:35'worked in a similar way.'
0:36:37 > 0:36:40Ears underwater were fluid-filled cavities
0:36:40 > 0:36:44and so sound could easily travel from the water
0:36:44 > 0:36:47into the underwater ear and it could easily be detected
0:36:47 > 0:36:50because there was liquid on both sides of that boundary.
0:36:52 > 0:36:55'But when that life came up into air,
0:36:55 > 0:36:57'suddenly the sound was in the air
0:36:57 > 0:36:59'but the ear was still filled with fluid
0:36:59 > 0:37:01'and that was a problem.'
0:37:07 > 0:37:11I've got a set up here that will show what happens when sound
0:37:11 > 0:37:15tries to travel across a boundary from air into water.
0:37:15 > 0:37:18I've got two microphones here. One's a normal microphone. This one.
0:37:18 > 0:37:21It's set up for hearing sound in air.
0:37:21 > 0:37:25And the other one is set up for hearing sound underwater, down here.
0:37:25 > 0:37:27That's called a hydrophone.
0:37:27 > 0:37:29I've got some tent pegs here.
0:37:29 > 0:37:33I could hear that quite easily and so could the microphone,
0:37:33 > 0:37:36so there's a great big spike on the microphone in air.
0:37:36 > 0:37:39But the hydrophone in water heard almost nothing.
0:37:39 > 0:37:41What's going on is that at the boundary,
0:37:41 > 0:37:44when there's air up here and water down here,
0:37:44 > 0:37:47and sound comes from the air and hits that boundary,
0:37:47 > 0:37:51because air is less dense and much easier to squash than water,
0:37:51 > 0:37:53instead of travelling through,
0:37:53 > 0:37:55that sound wave just bounces straight off.
0:37:55 > 0:37:58It doesn't get through the boundary.
0:38:07 > 0:38:10And this is the problem that early life faced.
0:38:10 > 0:38:13If you've got a fluid-filled ear, liquid-filled ear,
0:38:13 > 0:38:15it works perfectly underwater because sound can travel
0:38:15 > 0:38:18through the water into your liquid-filled ear
0:38:18 > 0:38:21and you can hear the sound. But once you put that in air,
0:38:21 > 0:38:23the sound comes in from the air
0:38:23 > 0:38:26but it hits your ear and bounces straight off.
0:38:26 > 0:38:28It can't get in to be detected.
0:38:29 > 0:38:33'The way sound behaves at a boundary between two mediums
0:38:33 > 0:38:38'hindered the ability of early land-based life to hear properly.
0:38:41 > 0:38:44The process of evolution came up with a really elegant solution
0:38:44 > 0:38:48to this problem, by moving around some very tiny bones.
0:38:48 > 0:38:51And here they are. These are life-size casts of them.
0:38:51 > 0:38:54And they're called the malleus, the incus and the stapes.
0:38:54 > 0:38:57The ossicles, which means "tiny bones".
0:38:57 > 0:39:00And they are the smallest bones in the body.
0:39:00 > 0:39:03And two of them were part of the jawbone in our marine ancestors
0:39:03 > 0:39:06but they moved into the middle ear and they do something very clever.
0:39:06 > 0:39:08By working together,
0:39:08 > 0:39:12they help move sound from the outside world into the cochlea.
0:39:21 > 0:39:24'The ossicles sit just in front of the cochlea.
0:39:26 > 0:39:31'And when sound hits the eardrum, these tiny bones are set in motion.
0:39:33 > 0:39:36'Moving efficiently as a set of levers
0:39:36 > 0:39:40'between the large eardrum and the tiny stapes.
0:39:43 > 0:39:47'This increases the energy that's transferred to the cochlea.
0:39:51 > 0:39:54'This sophisticated little mechanism acts as an amplifier
0:39:54 > 0:39:55'and it's really efficient.'
0:39:55 > 0:39:58What matters is the amount of sound energy
0:39:58 > 0:40:01that gets into the fluid inside the cochlea.
0:40:01 > 0:40:03And without this, it would be about 1%,
0:40:03 > 0:40:07but with a middle ear like this, it's about 60%.
0:40:07 > 0:40:10So, this is the crucial evolutionary step
0:40:10 > 0:40:13that allowed land-based mammals to develop such good hearing.
0:40:16 > 0:40:21'Hearing that allows us to detect a huge range of amplitudes.
0:40:22 > 0:40:25'Everything from the thundering roar of an engine...
0:40:27 > 0:40:30'..to the flapping of an insect's wings.
0:40:32 > 0:40:35'And hearing the very quiet end of this range
0:40:35 > 0:40:41'doesn't rely solely on the ear but also on what lies beyond it.
0:40:45 > 0:40:50'To experience this, I need to find something extremely rare.
0:40:50 > 0:40:52'Silence.
0:40:53 > 0:40:56'It doesn't exist in the natural world
0:40:56 > 0:41:00'so I've come here - the largest anechoic chamber in Britain.
0:41:03 > 0:41:08'It's been meticulously engineered to be incredibly quiet.
0:41:08 > 0:41:12'And it's here that I'll test my ears to their limit.'
0:41:18 > 0:41:21The idea of all this clobber is that I have to be in there
0:41:21 > 0:41:23completely on my own.
0:41:23 > 0:41:26So, there's no sources of sound and nothing to reflect off.
0:41:29 > 0:41:32So, this might be a moot point because I might decide I hate it
0:41:32 > 0:41:34after two minutes and that's all right.
0:41:34 > 0:41:37But if I'm all right after 20 minutes, is there any reason to...
0:41:37 > 0:41:40Does it get worse as you go? Because some people don't seem to mind it.
0:41:40 > 0:41:43I think it's completely individual and so you, kind of, see how it is.
0:42:05 > 0:42:10'All on my own, I can feel myself adjusting to this new environment.
0:42:12 > 0:42:15'I can't hear any sounds from outside.
0:42:16 > 0:42:18'It's the quietest place I've ever been.
0:42:25 > 0:42:31'And as I sit, the rustle of my clothes sounds strangely loud.
0:42:32 > 0:42:34HEART BEATING
0:42:36 > 0:42:39'I'm starting to notice the sounds of my own body.
0:42:42 > 0:42:44'The regular beating of my heart.
0:42:46 > 0:42:50'A background hiss, perhaps from the firing of my nerves.
0:42:54 > 0:42:56'The soft whisper of my breath.
0:43:00 > 0:43:04'Sounds that I don't ordinarily hear have now become dominant.'
0:43:17 > 0:43:20Oh, they're opening the door.
0:43:20 > 0:43:23I wonder what the outside world's going to be like now.
0:43:24 > 0:43:28'After 50 minutes, Dr Peter Keating arrives to explain
0:43:28 > 0:43:32'how I could hear so much in a place like this.
0:43:33 > 0:43:36- So, how was that? - It wasn't ever completely silent.
0:43:36 > 0:43:38My brain was always telling me it was hearing something
0:43:38 > 0:43:40but that something was very, very quiet.
0:43:40 > 0:43:43When you take external sounds away, which is what's happening here,
0:43:43 > 0:43:46then first of all you become more sensitive to the sounds
0:43:46 > 0:43:48that are inside your body.
0:43:48 > 0:43:51There's actually a little separate set of cells in your auditory nerve
0:43:51 > 0:43:53which are responsible for hearing very quiet sounds.
0:43:53 > 0:43:56So, in here, you were probably switching over to using those.
0:43:59 > 0:44:01'A specialised type of nerve fibre
0:44:01 > 0:44:06'carries very quiet sound signals from the cochlea to the brain,
0:44:06 > 0:44:10'where our sensitivity to this type of sound isn't fixed.
0:44:11 > 0:44:13The brain is constantly adapting,
0:44:13 > 0:44:16and so, if you take away loud sounds and you only have quiet sounds,
0:44:16 > 0:44:19the brain will get used to that over time.
0:44:19 > 0:44:22So, the physical hearing apparatus is staying the same
0:44:22 > 0:44:25- but our brains are what's doing the adapting?- Absolutely.
0:44:25 > 0:44:28So, when you came in here, in the first seconds to minutes,
0:44:28 > 0:44:31there would have been some changes going on in your brain.
0:44:31 > 0:44:34If you'd stayed in here for longer, if you'd stayed in for days, weeks,
0:44:34 > 0:44:36more changes would have happened.
0:44:36 > 0:44:37And if you'd stayed in here for months,
0:44:37 > 0:44:39even more changes would have happened.
0:44:39 > 0:44:42That's one of the things that we're finding out about the brain
0:44:42 > 0:44:45is that you can adapt to these changes in sensory input.
0:44:45 > 0:44:48Not just hearing, but in vision and all kinds of other sensory systems.
0:44:48 > 0:44:51And these can happen at all kinds of different timescales.
0:44:52 > 0:44:54'The processing power of our brain,
0:44:54 > 0:44:56'together with the mechanics of our ears,
0:44:56 > 0:44:59'forms an incredibly powerful and adaptive system
0:44:59 > 0:45:01'to listen in to the world.
0:45:22 > 0:45:25Understanding the physical properties of sound
0:45:25 > 0:45:29and being able to decipher them to learn about the world around us
0:45:29 > 0:45:31is a really powerful tool.
0:45:31 > 0:45:33But we're not limited to just listening in
0:45:33 > 0:45:36on what the environment sends to us.
0:45:36 > 0:45:41We can create our own sound to send it out to probe the world.
0:45:41 > 0:45:44And that can teach us about ourselves, our planet
0:45:44 > 0:45:46and even what's beyond that.
0:45:56 > 0:46:01'Sound has been especially useful in looking at things we can't see.
0:46:01 > 0:46:04'Things that are hidden from the world of light.
0:46:07 > 0:46:10'It began in the early years of the First World War,
0:46:10 > 0:46:13'when submarines became a deadly weapon.'
0:46:18 > 0:46:20EXPLOSION
0:46:20 > 0:46:22'Almost invisible,
0:46:22 > 0:46:25'these machines would drive the Allies
0:46:25 > 0:46:27'to develop new detection technology.
0:46:30 > 0:46:34'Sound can travel exceptionally long distances underwater
0:46:34 > 0:46:39'and so acoustic echo ranging, or sonar, offered an obvious solution.
0:46:42 > 0:46:45'And after the Second World War had come to an end,
0:46:45 > 0:46:48'the rapid advancements of underwater acoustics continued.
0:46:51 > 0:46:54'Our relationship with the oceans can be limited.
0:46:54 > 0:46:57'Quite often you look out over the sea and what you see is this.
0:46:57 > 0:47:01'It's grey and opaque, you can't see through the surface.
0:47:01 > 0:47:02'It looks a little bit dull.'
0:47:03 > 0:47:07But underwater acoustics changed all of that.
0:47:07 > 0:47:10Once you can use sound to explore the underwater world,
0:47:10 > 0:47:13you're not limited to looking for submarines.
0:47:14 > 0:47:17'Today, even as we reach for the stars,
0:47:17 > 0:47:22'we know less about this ocean than we do the surface of the moon.'
0:47:22 > 0:47:25'By the 1950s, oceanographers across the world
0:47:25 > 0:47:27'were using military sonar technology
0:47:27 > 0:47:30'to look down at the deep ocean floor,
0:47:30 > 0:47:33'which, for centuries, we could only imagine.
0:47:36 > 0:47:39'They discovered an extraordinary underwater landscape
0:47:39 > 0:47:42'of towering mountains and deep trenches.
0:47:45 > 0:47:48'Sound played a key role in understanding
0:47:48 > 0:47:51'the magnificent structures of our world.'
0:47:51 > 0:47:55The oceans are one of the most important features of our planet
0:47:55 > 0:47:59and they're not just the filler between the interesting bits.
0:47:59 > 0:48:01Once you can see them properly,
0:48:01 > 0:48:04you can see the oceans become a place.
0:48:10 > 0:48:14'Today, sonar doesn't just show us large-scale structures,
0:48:14 > 0:48:17'it can also reveal exquisite detail.'
0:48:17 > 0:48:19- Welcome aboard.- Thank you.
0:48:19 > 0:48:23'Which, until recently, had been a job only our eyes could perform.
0:48:24 > 0:48:28'This is the North Sea, off the coast of Suffolk.'
0:48:30 > 0:48:33Looks just like an ordinary bit of ocean
0:48:33 > 0:48:36but there is an archaeological site down there,
0:48:36 > 0:48:38so I'm going down to have a look.
0:48:38 > 0:48:41I have a lot of layers to put on.
0:48:42 > 0:48:43Oops. The other way round.
0:48:54 > 0:48:58Right, it's definitely cold in the North Sea!
0:48:58 > 0:49:00- I can't actually see you. - You can't see me at all?
0:49:00 > 0:49:04- Unless you come in really close. - So...- Yeah, it's just so brown.
0:49:04 > 0:49:06I've got my glove here.
0:49:06 > 0:49:11And if I hold that out, in front of my face underwater, you can't
0:49:11 > 0:49:14see anything, so I can't see this far in front of my face.
0:49:14 > 0:49:18And the reason it's this brown, horrible colour,
0:49:18 > 0:49:21is that the water is clearly full of sediment.
0:49:21 > 0:49:25There's tiny little particles of silt and sand.
0:49:25 > 0:49:27And so seeing anything...
0:49:27 > 0:49:29is virtually impossible.
0:49:33 > 0:49:35'Even though we're near the coast,
0:49:35 > 0:49:38'where the water isn't particularly deep,
0:49:38 > 0:49:40'the visibility is still appalling.'
0:49:44 > 0:49:46That's... That's terrifying.
0:49:47 > 0:49:52I was only going down a metre or two and it's completely black.
0:49:52 > 0:49:54Like, absolutely dark.
0:49:54 > 0:49:57'Since I couldn't see anything for myself,
0:49:57 > 0:50:01'Professor David Sear explains what lies beneath us.'
0:50:01 > 0:50:05When I was down there a little while ago I couldn't see anything.
0:50:05 > 0:50:06So, what is down there?
0:50:06 > 0:50:10Well, actually, down there is one of the largest archaeological sites
0:50:10 > 0:50:12in the world, called Dunwich.
0:50:12 > 0:50:15Dunwich, to a lot of people, is just a small village.
0:50:15 > 0:50:18800 years ago it was the sixth largest international port
0:50:18 > 0:50:19in the North Sea.
0:50:19 > 0:50:23And the story of Dunwich is one of coastal erosion.
0:50:23 > 0:50:27Coastal erosion driven by a series of very large storms.
0:50:27 > 0:50:29So, this sounds like the perfect job for sonar.
0:50:29 > 0:50:31What do you see when you look with sonar?
0:50:31 > 0:50:34Sonar enabled us to cover a large area
0:50:34 > 0:50:37and we were able to see that there were indeed structures.
0:50:37 > 0:50:40The important thing was that we didn't know whether they were
0:50:40 > 0:50:44geology or were they actually parts of churches and buildings?
0:50:44 > 0:50:46So, what you ideally need is a technology
0:50:46 > 0:50:49that is able to see through this turbid, muddy water
0:50:49 > 0:50:53with the detail to enable you to see individual,
0:50:53 > 0:50:57say, carved blocks or other evidence of it being made by people.
0:50:57 > 0:51:00We came across a technology that is relatively new
0:51:00 > 0:51:02and it does just that.
0:51:04 > 0:51:08It uses sound to project... A bit like a torch beam, but sound.
0:51:08 > 0:51:11And you don't do that from a boat?
0:51:11 > 0:51:13You don't. You have to send a diver down
0:51:13 > 0:51:18and that diver sees what the sound is illuminating, if you like,
0:51:18 > 0:51:19in their visor.
0:51:26 > 0:51:28'Sound waves from surface-based sonar
0:51:28 > 0:51:32'can travel easily through the water, which provided David
0:51:32 > 0:51:34'with the layout and general structure
0:51:34 > 0:51:37'of this two-kilometre-squared site.
0:51:38 > 0:51:41'Yet it was the much higher frequency sound waves
0:51:41 > 0:51:45'from the sonar camera that gave David what he really needed.
0:51:45 > 0:51:48'Although these sound waves can't travel as far,
0:51:48 > 0:51:51'they can create much more detailed images,
0:51:51 > 0:51:54'and showed that what lay beneath the waves
0:51:54 > 0:51:57'were structures with sharp straight edges.
0:51:58 > 0:52:01'Edges that could only have been made by man.'
0:52:09 > 0:52:11The first time we saw this imagery,
0:52:11 > 0:52:15looking at it in real-time as the diver saw it, it was fantastic,
0:52:15 > 0:52:19because you could see great blocks of masonry, made of flints,
0:52:19 > 0:52:23rubble, mortar, just like the churches today on land.
0:52:23 > 0:52:25You see it on the seabed.
0:52:25 > 0:52:28That nailed it for us. It was the evidence we needed
0:52:28 > 0:52:31to move from the historical accounts to the reality of,
0:52:31 > 0:52:34yes, these are the ruins of churches from medieval Dunwich.
0:52:34 > 0:52:37'Sending sound waves through the ocean
0:52:37 > 0:52:39'has unlocked marine archaeology,
0:52:39 > 0:52:43'uncovering the human stories hidden beneath the sea.
0:52:50 > 0:52:54'We're continually getting better at detecting and controlling
0:52:54 > 0:52:56'the nuances of sound waves
0:52:56 > 0:53:00'and at using them as tools for probing and manipulating our world.
0:53:01 > 0:53:04'But there are other worlds out there.
0:53:05 > 0:53:08'Even though sound can't travel across the solar system,
0:53:08 > 0:53:12'every planet and moon is like a little bubble of sound
0:53:12 > 0:53:15'isolated from us by the vacuum of space.
0:53:16 > 0:53:19'And there's a huge amount to learn from those little bubbles of sound,
0:53:19 > 0:53:22'if only we can listen in.'
0:53:23 > 0:53:26'Three, two, one...
0:53:26 > 0:53:29'And lift-off of the Cassini spacecraft!'
0:53:29 > 0:53:33'In 1997, one of the largest spacecraft ever launched
0:53:33 > 0:53:37'started its billion-kilometre journey.'
0:53:38 > 0:53:40'We have cleared the tower
0:53:40 > 0:53:43'and the Cassini spacecraft is on its way to Saturn.'
0:53:47 > 0:53:52'In 2005, Cassini sent a probe called Huygens to Titan,
0:53:52 > 0:53:55'the largest of Saturn's moons,
0:53:59 > 0:54:04'A world shrouded by a thick, opaque atmosphere...
0:54:06 > 0:54:10'..making it almost impossible to explore from a distance.
0:54:13 > 0:54:17'So, for decades, this moon remained much of a mystery.'
0:54:20 > 0:54:24Huygens is still the only probe to have successfully landed
0:54:24 > 0:54:26in the outer solar system.
0:54:26 > 0:54:30And as it deployed its parachutes and started this two-and-a-half-hour
0:54:30 > 0:54:34drift down through the atmosphere of Titan towards the surface,
0:54:34 > 0:54:38there was a suite of instruments on the probe measuring all sorts
0:54:38 > 0:54:40of things about the environment and the conditions.
0:54:40 > 0:54:44And some of those instruments were recording sound.
0:54:46 > 0:54:51'Around 160km above the surface of Titan,
0:54:51 > 0:54:54'Huygens deployed a microphone,
0:54:54 > 0:54:57'which recorded the sounds of Titan's atmosphere.
0:55:02 > 0:55:05SOUND OF STRONG WIND
0:55:11 > 0:55:12And this is it.
0:55:12 > 0:55:15This is what the microphone on Huygens heard
0:55:15 > 0:55:18as it fell through Titan's atmosphere.
0:55:19 > 0:55:23What you're hearing is the roaring of the wind going past the probe
0:55:23 > 0:55:27and the probe falling down through the atmosphere.
0:55:27 > 0:55:32This is the sound of an alien world, and this was only the start.
0:55:37 > 0:55:41'Another instrument used sonar to detect the surface
0:55:41 > 0:55:44'during the final 90 metres of the descent.
0:55:44 > 0:55:48'It showed that Titan's terrain rises and falls.
0:55:49 > 0:55:52'That the surface is relatively smooth,
0:55:52 > 0:55:54'not dissimilar to gravel,
0:55:54 > 0:55:57'and that this surface is likely to be damp.'
0:55:58 > 0:56:01This is the landscape that Huygens landed on.
0:56:01 > 0:56:05Sonar was one of the tools that helps us understand it.
0:56:06 > 0:56:09Even if a planet or a moon hasn't got an atmosphere,
0:56:09 > 0:56:12sound can still be generated and transmitted through its liquid
0:56:12 > 0:56:16and solid layers, so potentially, if you sent an acoustic probe
0:56:16 > 0:56:20to another world, you might hear the sound of thunder,
0:56:20 > 0:56:22or hear meteorite strikes,
0:56:22 > 0:56:25or the flow of rivers. Perhaps rivers of methane.
0:56:25 > 0:56:27Or the sound of rain.
0:56:27 > 0:56:30And as more and more missions are sent out into the solar system
0:56:30 > 0:56:34to explore, acoustic probes are going to become more and more common
0:56:34 > 0:56:38as a way of exploring not just our world but others.
0:57:03 > 0:57:07'We live in a dynamic, pulsating world of sound
0:57:07 > 0:57:10'and it touches our skin and our clothes and our lives every day.'
0:57:10 > 0:57:14We can only tap into it because we have these two complex,
0:57:14 > 0:57:17sensitive detectors on either side of our head,
0:57:17 > 0:57:20but that's enough to sense the riches.
0:57:26 > 0:57:28Sound is so important for our species.
0:57:28 > 0:57:31It's deeply embedded in our culture
0:57:31 > 0:57:34and it's allowing us to push our technological boundaries
0:57:34 > 0:57:36to better understand our world.
0:57:36 > 0:57:40And the best thing about it is that that world of sound is right here.
0:57:40 > 0:57:42All you have to do is listen.
0:57:42 > 0:57:45FIREWORKS
0:57:52 > 0:57:55If you'd like to find out more about the science of sound
0:57:55 > 0:57:59and how we hear sound, go to the BBC website on screen
0:57:59 > 0:58:02and follow the links to the Open University.