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TWEETING BIRDS
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BUZZING BEES
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This is a familiar scene.
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It's the Somerset countryside on a calm day.
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And it sounds familiar.
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I can hear the birds singing,
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I can hear the wind rustling through the trees
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and I can hear the insects around me.
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This isn't just a landscape, it's a soundscape.
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A constant flood of sound waves washing over me from all directions.
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'No matter where we are or where we go, sound is always present.
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'And each individual noise offers us information about our world
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'from a moment in time and space.
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'Every sound wave carries a story about where it's come from
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'and the journey it's been on.'
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And our evolutionary history has given us these two detectors
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for tapping into those stories.
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What we hear shapes our understanding of our world.
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'In this programme, I'm going to explore how we exploit,
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'manipulate and control sound.'
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Just the quality of the sound says something's not right in here.
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'I'll delve into the complex ways in which our own bodies
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'precisely decode the information carried in sound waves.'
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That's amazing.
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When you take it off I can hear nothing.
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It's incredible!
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'And how the more we've come to understand sound,
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'the more we've been able to use it
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'to make remarkable discoveries about life...
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'..our planet...
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'..and even the solar system.'
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'In our normal everyday lives, it's hard to really appreciate
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'how much information sound carries.'
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- Want to put the helmet on?
- OK.
- You need those, as well.
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'Which is why acoustic engineer Professor Trevor Cox is taking me
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'to a hidden location deep inside the hills of Scotland.
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'Where, in the absence of light, hearing becomes my primary sense.'
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I'm going to go in first, so I shall demonstrate.
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It's ever so slightly sinister, this, isn't it?
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- There's your helmet.
- OK.
- You want to put your gloves on.
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I've probably have nightmares about doing something like this.
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Slide yourself in.
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Now, just be really careful as you get up. A bit further.
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- OK?
- What have I arrived into?
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I'm going to be slightly cruel and turn my head torch off
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so we can't really see.
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We're just really working with the acoustic here.
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You have one of those. Shall we wander in just a bit further?
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Very, very dark, isn't it?
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- Watch where you walk.
- Urgh, that's horrid.
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This is where the baddie turns up, right?
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Two people walk into a dark space
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and just the quality of the sound says something's not right here.
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'Just from the way that sounds behave in this place,
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'I'm beginning to piece together a picture of what it might be like.'
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What do you think this space is?
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So, it feels like it's gigantic.
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I can't tell because I can't see anything but it feels as though
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it could be enormous - the size of a cathedral or bigger.
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Just because that's the only place
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I've heard this sort of thing happen to my voice before.
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I'm finding it hard to finish a sentence because I keep saying
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a word and then stopping to listen to what it sounds like.
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When you listen to a sound in a room you can get a lot of information.
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You'll get the sound straight from me to you
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and then all the walls are contributing reflections -
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the sound's bouncing around the room.
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All the time in a space we're listening for these sort of clues.
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But we're not usually that, you know, conscious we're doing it.
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'The ability of sound to reflect is one of the most critical ways
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'it can carry information.
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'But sound reflections can tell me more than the size of a place.
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'I just need a different type of sound.'
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- I've got a stopwatch for you there.
- OK.
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- So, if you could wait for... hear the bang.
- Yeah.
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And then just measure how long it takes the sound to decay to nothing,
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which is actually how they first measured reverberation.
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- I shall retreat to a safe distance.
- Yeah!
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I just dropped it.
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I can't see...
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LOUD BANG
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SOUND SLOWLY DIMINISHES
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57 seconds.
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Wow.
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This place actually holds the world record
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for the longest reverberation time,
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which is what you kind of measured there.
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What's going on to make that happen?
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First of all, it's a very big place.
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But there must be something more than that
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because if you go into St Paul's Cathedral in London,
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the sound would only last about ten seconds before dying away.
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The sound is being contained and held in this giant space.
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And that's because the walls here are incredibly massive.
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You can tell that this must have hard, heavy walls,
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whereas if you brought a lot of soft furnishings in,
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which absorb sound, this place would go dead.
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So, we're getting extra information
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because sound reflects differently off different materials.
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What is this place? After all that, where are we?
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Well, let's put the lights on.
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So, this is a massive space.
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It's about a quarter of a kilometre long
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so that's where a lot of the reverberations come.
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- What's it doing here?
- Well, it's actually an oil storage depot
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which was built in the run-up to World War II
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to protect the Royal Navy shipping oil from bombing.
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So, it's been made bombproof
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and that's the reason it's got this huge reverberance.
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They've made it out of half-metre-thick concrete
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and behind it is the bedrock of Scotland.
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So, this is really massive walls.
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And the walls are covered in oil, as well. It's horribly sticky.
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Sticky on your feet, everywhere. That's really useful acoustically.
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Concrete's a bit porous so normally you get a little bit of absorption
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but its pores have been gunked up with oil.
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So, what's happening is that the sound is reflecting off the walls
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really efficiently, it's not getting absorbed.
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You can get a tremendous lot of information by looking at
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the pattern of reflections, and, as an acoustic engineer,
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that's what you do when you design a grand concert hall.
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SAXOPHONE REVERBERATES
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You try and design the pattern of reflections
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to be just right to enhance the music.
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SAXOPHONE REVERBERATES
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'The reason that sound can carry so much information
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'is because of its fundamental nature.
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'It travels as a wave.
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'And every time a sound wave reflects off a surface
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'it's changed in subtle ways.'
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Reflection is a way of redirecting sound
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and that redirected sound carries information
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about the obstacle it bounced off.
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We use that acoustic signature to learn about our environment
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in a general way, but there are animals that absolutely rely on it,
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and they are the true masters of sound.
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'For most bats, hearing is their primary sense.
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'Listening to sound reflections is key to their survival.
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'And their success has driven complex relationships
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'with other creatures that live in and exploit this auditory world.
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'Bats are one of the loudest creatures in the animal kingdom.
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'We can't hear them because they mostly use frequencies
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'our ears can't detect, making it quite difficult for bat experts
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'like Dr Marc Holderied to study them.'
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We have an acoustic camera that can pick up ultrasound
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and we've just put it in one of my favourite research spots.
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So, this is a commuting corridor
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with loads of bats using it every night.
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And this acoustic camera now shows me what is going on
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as we look at this screen.
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We've just seen two bats flying and there's a third one.
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So, there's a whole group flying past.
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You can see all these whitish yellowish blobs there.
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As the bat was flying past
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it was emitting these ultrasonic frequencies.
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So, you're looking for patterns?
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We can look at this spectrogram display down here
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and try and find out which species we were looking at.
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There's another one coming right now.
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Now, if you look at that, they all ended about the same frequency.
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They're around 45 kilohertz,
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which tells us that this is a common pipistrelle.
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And just now is a very different call.
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And I can tell you that this is a Daubenton's bat.
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So, you're painting this picture of all these bats whooshing past us,
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making sounds that we can't hear.
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If we could hear them, what would we hear?
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What I've brought along here is a tiny bat detector.
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It turns the ultrasonic frequencies into audible frequencies.
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- That was a bat!
- There's one flying over right now.
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We heard this very quick succession of calls there.
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There it is again. Very good. It just whizzed over there.
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So, they're very short and sharp and even though that sounds very quick
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- to us, there's a lot going on between one pulse and the next.
- Yes.
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They send out the high-intensity sound...
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..and then they hit all the obstacles that are in the area.
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These obstacles produce echoes
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and the bat then waits for these to come back.
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The further away an object is, the longer the echo takes to return
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to the bat and this is how bats measure distance.
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And that is an incredibly complex achievement.
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There is so many different reflectors, like all the leaves,
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you have the ground, you have all the branches,
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and all of them produce echoes.
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'Bats evolved the ability to use sound to see
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'at least 53 million years ago...
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'..giving them an enormous advantage when hunting for prey
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'under the cover of darkness.'
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So, we've got a moth here. What species is it?
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It's a heart and dart.
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It's got this beautiful gold sheen.
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Yeah, yeah, yeah, they are quite beautiful.
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And how's a bat going to find this moth?
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So, a bat uses biosonar not only for navigation but also to capture prey.
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So, when they are searching for insects, they want to look very far.
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So, what they use is their lowest frequency calls that carry very far.
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But as soon as they've detected the moth,
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they add in higher frequencies to their calls.
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BAT CALLS
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Higher frequencies have shorter wavelength
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and give them better resolution.
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And better resolution means they can localise the moth very well.
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BAT CALLS
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And the bat sonar is giving it a brilliant tool
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for finding these very fast-moving moths.
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Do they have it all their own way?
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Moths, of course, are fighting back.
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All these moths had to do is evolve an ultrasound sensitive ear
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that picks up the frequencies the bats emit, and they did.
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- So, can this moth hear?
- This moth has ears, yes.
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When they hear a bat that's far away,
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they just steer out of harm's way.
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And so, there's, sort of, one of these arms races going on
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where one species makes a change that makes them more successful
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and then their prey species also has to adapt.
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So... Oh, it's going for a walk again.
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And are there any other strategies that a moth could take
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- to avoid this bat that's coming to get it for dinner?
- Yes.
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Moths have taken the next step.
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Moths have evolved a jamming mechanism
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that helps them throw the biosonar off target.
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You have a moth that knows it's under attack,
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it produces ultrasonic clicks.
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And these ultrasonic clicks are in the similar frequency range
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as the echoes a bat is expecting.
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But if it hears these clicks rather than the echoes
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it can't really make out a full echolocation picture any more.
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And that gives the moth the time to just whizz out of the way.
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MOTH CLICKS
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'This sophisticated interplay between bats and moths
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'shows just how rich in information
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'and how valuable reflecting sound waves can be.
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'But reflections are not the only way sound waves help us
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'understand our surroundings.
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'There's another feature of sound that can provide us with
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'even more information about the world.
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'And it's particularly useful in warning us of approaching danger.
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CAR HORN
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AMBULANCE SIREN
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LOUD TRAFFIC NOISES
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I live in London and I cycle all the time
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and it's easily the most dangerous thing I do on a daily basis.
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There's so much traffic here.
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Vans like that that overtake you when you're not expecting them.
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What I'm conscious of is paying attention to light.
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I can see what's in front of me, I look behind me,
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that makes me feel secure.
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But I'm getting a lot of extra information from sound.
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Two things that really worry me when I'm cycling,
250
00:15:50,520 --> 00:15:52,760
and they are big trucks and motorcycles.
251
00:15:52,760 --> 00:15:55,760
Fortunately, both of them make a huge amount of noise.
252
00:15:55,760 --> 00:15:57,280
That was a motorbike.
253
00:15:57,280 --> 00:16:00,160
And you can hear them coming, even from around the corner.
254
00:16:00,160 --> 00:16:02,040
LOUD MOTORCYCLE ENGINE
255
00:16:02,040 --> 00:16:04,040
I certainly heard him.
256
00:16:06,280 --> 00:16:09,040
'We can often hear things we can't see
257
00:16:09,040 --> 00:16:13,280
'because, unlike light, sound can travel around corners.
258
00:16:18,760 --> 00:16:21,760
'It's something made possible when a fundamental feature
259
00:16:21,760 --> 00:16:25,520
'of the sound wave is just right - its size.'
260
00:16:25,520 --> 00:16:27,280
It works a bit like this.
261
00:16:27,280 --> 00:16:29,960
If we imagine we've got an obstacle in the way
262
00:16:29,960 --> 00:16:32,760
and in this case that could be the corner of a building.
263
00:16:32,760 --> 00:16:35,280
I'm going to draw a sound source over here.
264
00:16:35,280 --> 00:16:39,200
Sound is spreading out in ripples, like the ripples on a pond.
265
00:16:39,200 --> 00:16:42,120
So, as the sound travels away, those ripples spread out.
266
00:16:42,120 --> 00:16:44,520
They can spread around the corner.
267
00:16:44,520 --> 00:16:48,280
So, if I was standing here, I might not be able to see the sound source
268
00:16:48,280 --> 00:16:50,840
but I would be able to hear the sound.
269
00:16:50,840 --> 00:16:52,760
And this is called diffraction.
270
00:16:52,760 --> 00:16:55,480
It doesn't work in the same way for all wavelengths
271
00:16:55,480 --> 00:16:58,040
because diffraction depends on how the wavelength
272
00:16:58,040 --> 00:17:00,280
is related to the size of the obstacle.
273
00:17:00,280 --> 00:17:02,440
And a corner of a building is quite big.
274
00:17:02,440 --> 00:17:06,520
So, this time I'm going to draw a higher frequency sound
275
00:17:06,520 --> 00:17:09,040
which means the wavelengths are much shorter.
276
00:17:09,040 --> 00:17:13,200
So, they'll spread out like ripples and they will diffract a little bit
277
00:17:13,200 --> 00:17:17,480
as they go around the corner but not nearly as much.
278
00:17:17,480 --> 00:17:20,280
So, sound that might be a wavelength of a few centimetres
279
00:17:20,280 --> 00:17:22,760
are much smaller than the corner of the building
280
00:17:22,760 --> 00:17:25,280
so I can't hear the high frequencies here
281
00:17:25,280 --> 00:17:27,240
but I can hear the low frequencies.
282
00:17:31,280 --> 00:17:33,760
'Most sounds can travel around objects
283
00:17:33,760 --> 00:17:36,280
'because their wavelength is relatively big.
284
00:17:37,280 --> 00:17:40,800
'Light, on the other hand, has a very short wavelength.
285
00:17:43,040 --> 00:17:45,760
'Which means there are very few things in our world
286
00:17:45,760 --> 00:17:47,760
'that it can bend around.
287
00:17:47,760 --> 00:17:51,040
'Instead, light stops and casts a shadow.
288
00:17:59,280 --> 00:18:03,040
'The ease with which sound can travel around the environment
289
00:18:03,040 --> 00:18:07,040
'has played an important role in the story of our survival.
290
00:18:08,040 --> 00:18:11,040
'Because it means we can hear the roar of a hungry lion
291
00:18:11,040 --> 00:18:15,280
'or the rumble of a truck - even if we can't see them.'
292
00:18:15,280 --> 00:18:18,280
The diffraction of sound does more than just let me know
293
00:18:18,280 --> 00:18:21,040
that there's a sound source somewhere near me.
294
00:18:21,040 --> 00:18:25,640
It helps me pinpoint exactly where that sound source is.
295
00:18:33,080 --> 00:18:36,040
'This ability is called localisation.
296
00:18:38,120 --> 00:18:42,280
'Every animal needs to know which direction danger is coming from.
297
00:18:43,280 --> 00:18:47,120
'It works because sound doesn't just diffract around our environment,
298
00:18:47,120 --> 00:18:50,040
'but also around the listener.
299
00:18:55,560 --> 00:18:59,280
'Dr Jenny Bizley is here to show me the complex mechanisms
300
00:18:59,280 --> 00:19:01,760
'we use to localise sound.'
301
00:19:01,760 --> 00:19:04,760
So, I don't know where the sound's going to come from?
302
00:19:04,760 --> 00:19:07,520
No, so if you face the front, I'll play a sound
303
00:19:07,520 --> 00:19:11,040
and then you can maybe point to where you think it comes from.
304
00:19:11,040 --> 00:19:12,520
No pressure!
305
00:19:13,760 --> 00:19:16,280
LOUD MONKEY CHATTER Oh, it's loud, isn't it?
306
00:19:16,280 --> 00:19:18,840
- Somewhere over there.
- Yeah, that's right.
307
00:19:18,840 --> 00:19:20,560
We'll try another one.
308
00:19:20,560 --> 00:19:23,040
GRUNTING Up there!
309
00:19:24,040 --> 00:19:26,040
Yeah. And how about this one?
310
00:19:26,040 --> 00:19:29,120
LOUD WHOOSHING Somewhere up there.
311
00:19:29,120 --> 00:19:32,640
CRASHING Something broke over there.
312
00:19:32,640 --> 00:19:34,520
'Although I'm not conscious of it,
313
00:19:34,520 --> 00:19:38,040
'my brain is precisely locating each sound I'm hearing.'
314
00:19:38,040 --> 00:19:40,760
So, the biggest bee in the world is over there!
315
00:19:40,760 --> 00:19:42,520
Oh, it's moving.
316
00:19:42,520 --> 00:19:45,760
'And it's not limited to fixed sounds.
317
00:19:48,960 --> 00:19:51,760
'To understand how we localise sound,
318
00:19:51,760 --> 00:19:55,040
'we need to look at the way it moves around our bodies
319
00:19:55,040 --> 00:19:59,040
'and interacts with the two ears on opposite sides of our head.'
320
00:20:00,040 --> 00:20:02,520
So, we're going to play the sound of the twig snapping
321
00:20:02,520 --> 00:20:05,280
that you heard previously from one of the speakers over there,
322
00:20:05,280 --> 00:20:07,280
and it was coming from the left of the head.
323
00:20:07,280 --> 00:20:09,760
And we'll look at the input from the microphones on here.
324
00:20:09,760 --> 00:20:12,280
So, we should see the sound waves coming in here.
325
00:20:12,280 --> 00:20:13,920
TWIG SNAPPING
326
00:20:13,920 --> 00:20:16,240
So, this is the signal from the first microphone,
327
00:20:16,240 --> 00:20:17,280
which is on the left,
328
00:20:17,280 --> 00:20:19,760
and this is the signal from the right microphone.
329
00:20:20,760 --> 00:20:22,760
- And they look very different.
- Yes.
330
00:20:22,760 --> 00:20:25,760
You can see that the left-hand microphone is picking up a signal
331
00:20:25,760 --> 00:20:28,040
that's much louder than the signal on the right.
332
00:20:28,040 --> 00:20:29,760
And it's also arriving sooner.
333
00:20:29,760 --> 00:20:32,760
The timing difference, how long is that from there to there?
334
00:20:32,760 --> 00:20:36,040
From there to there is about 500 microseconds.
335
00:20:36,040 --> 00:20:38,040
So, just about half of a millisecond.
336
00:20:38,040 --> 00:20:39,760
So, the sound reached my left ear
337
00:20:39,760 --> 00:20:42,240
- half a millisecond before it reached my right ear?
- Yeah.
338
00:20:42,240 --> 00:20:43,800
We can measure that difference
339
00:20:43,800 --> 00:20:46,840
because sound moves relatively slowly, at least compared to light.
340
00:20:46,840 --> 00:20:50,040
The difference in timing is useful for low-frequency sounds.
341
00:20:50,040 --> 00:20:53,000
Because the low-frequency sound has quite a long wavelength,
342
00:20:53,000 --> 00:20:55,040
longer than the width of the head,
343
00:20:55,040 --> 00:20:58,040
the sound can diffract around the head to the far ear,
344
00:20:58,040 --> 00:20:59,880
but it does so with a delay.
345
00:20:59,880 --> 00:21:03,040
The other big difference here is the amplitude - the level of the sound.
346
00:21:03,040 --> 00:21:06,040
What's the level difference between one ear and the other?
347
00:21:06,040 --> 00:21:09,280
For this sound, we have a difference of the order of a few decibels,
348
00:21:09,280 --> 00:21:12,040
5-10, depending on the frequency of the sound.
349
00:21:12,040 --> 00:21:15,040
- So, that's quite a lot, is it?
- That's quite a large difference.
350
00:21:15,040 --> 00:21:17,280
The amplitude difference is important really
351
00:21:17,280 --> 00:21:20,800
for high-frequency sounds which have shorter wavelengths.
352
00:21:20,800 --> 00:21:23,040
They are not able to diffract around the head
353
00:21:23,040 --> 00:21:25,040
and they are shadowed by the head.
354
00:21:25,040 --> 00:21:28,200
So, the signal will be louder in the near ear and quieter in the far ear.
355
00:21:28,200 --> 00:21:31,280
These signals are kept within the brain and they're kept separately
356
00:21:31,280 --> 00:21:34,280
until higher up, sort of, in the processing hierarchy,
357
00:21:34,280 --> 00:21:37,280
when they're put together to give you a perception of space.
358
00:21:37,280 --> 00:21:40,040
And that means that, within seconds, you can tell where a sound
359
00:21:40,040 --> 00:21:43,280
comes from so that you can avoid it if it's going to eat you, or...
360
00:21:43,280 --> 00:21:45,640
I definitely avoid sounds that are going to eat me!
361
00:21:49,280 --> 00:21:53,360
'However, this system only works for localising sound
362
00:21:53,360 --> 00:21:55,280
'in the horizontal plane.
363
00:21:58,760 --> 00:22:02,280
'To know whether the sound is coming from above or below,
364
00:22:02,280 --> 00:22:06,840
'we use a trick that depends on the shape of each individual ear.
365
00:22:13,520 --> 00:22:17,280
'To show me, Jenny has kindly brought with her what looks like
366
00:22:17,280 --> 00:22:19,520
'an awful lot of Blu-Tack.'
367
00:22:19,520 --> 00:22:21,040
You know at school,
368
00:22:21,040 --> 00:22:24,280
teachers were always taking Blu-Tack out of people's ears.
369
00:22:24,280 --> 00:22:26,760
Somehow, you get older, and you become a scientist
370
00:22:26,760 --> 00:22:28,760
and it works the other way around.
371
00:22:28,760 --> 00:22:32,040
'The aim is to smooth out the folds of my outer ear.'
372
00:22:32,040 --> 00:22:34,200
There you are. Take your finger out.
373
00:22:34,200 --> 00:22:37,040
OK, now I've got ears full of Plasticine. Brilliant!
374
00:22:37,040 --> 00:22:41,160
Sound can still go down there but it can't bounce off all of this.
375
00:22:41,160 --> 00:22:43,520
I'm going to clap somewhere in front of you
376
00:22:43,520 --> 00:22:46,040
and you should just close your eyes and then point at it.
377
00:22:46,040 --> 00:22:47,760
OK, all right.
378
00:22:48,760 --> 00:22:50,040
Erm, there?
379
00:22:51,040 --> 00:22:52,520
No?!
380
00:22:52,520 --> 00:22:55,280
OK, give me another try, give me another try. Go on.
381
00:22:56,760 --> 00:22:58,280
- Down there?
- No.
382
00:22:59,520 --> 00:23:01,160
There?
383
00:23:01,160 --> 00:23:03,680
So, I'm rubbish at this with these in my ears.
384
00:23:03,680 --> 00:23:06,040
I'm going to take these out because they're doing...
385
00:23:06,040 --> 00:23:08,520
It does make the world sound very weird, actually.
386
00:23:08,520 --> 00:23:12,040
When I've got them in, it's like there's less going on
387
00:23:12,040 --> 00:23:14,800
and I take them out and suddenly the world opens out.
388
00:23:14,800 --> 00:23:17,760
You're just missing that information that you're used to having.
389
00:23:17,760 --> 00:23:21,440
'Ordinarily, sound waves will interact with my outer ear
390
00:23:21,440 --> 00:23:23,280
'before travelling inside.'
391
00:23:23,280 --> 00:23:25,760
When I clap, I make a broadband sound,
392
00:23:25,760 --> 00:23:27,760
so it has many sound frequencies in it.
393
00:23:27,760 --> 00:23:30,280
As the sound comes in, depending on where it comes from,
394
00:23:30,280 --> 00:23:32,280
it'll hit different parts of your ear.
395
00:23:32,280 --> 00:23:34,520
As it hits these complicated folds,
396
00:23:34,520 --> 00:23:38,040
some sound frequencies are made louder and others are made quieter,
397
00:23:38,040 --> 00:23:41,280
and your brain's learned over time how to interpret these changes
398
00:23:41,280 --> 00:23:44,080
that occur, according to where the sound comes from.
399
00:23:44,080 --> 00:23:47,520
You're listening for really subtle changes in the frequency composition
400
00:23:47,520 --> 00:23:49,520
of the sound that are introduced by
401
00:23:49,520 --> 00:23:51,680
the folded structure of the outer ear.
402
00:23:51,680 --> 00:23:55,520
So, the ear here is not just guiding sound in, this outer bit,
403
00:23:55,520 --> 00:23:57,120
it's actually changing it.
404
00:23:57,120 --> 00:23:59,440
So, it's really clever. That's really complicated
405
00:23:59,440 --> 00:24:01,040
and really clever at the same time.
406
00:24:01,040 --> 00:24:03,520
It is really clever and you have to learn to do it.
407
00:24:03,520 --> 00:24:05,280
Everyone's ears are different
408
00:24:05,280 --> 00:24:08,360
and the peculiarities of your outer ear are special to you.
409
00:24:10,760 --> 00:24:14,040
'The properties of sound waves and the way they travel
410
00:24:14,040 --> 00:24:17,040
'carry important messages about our environment.
411
00:24:22,840 --> 00:24:26,960
'But once those messages enter our ears, they need to be translated.'
412
00:24:32,040 --> 00:24:35,280
In order to access this information that's all around us,
413
00:24:35,280 --> 00:24:37,040
we need a detector.
414
00:24:37,040 --> 00:24:40,520
Something that can convert these tiny vibrations of the air
415
00:24:40,520 --> 00:24:43,200
into a signal our brain can understand.
416
00:24:44,760 --> 00:24:47,280
'Most of us take hearing for granted,
417
00:24:47,280 --> 00:24:51,800
'because it happens apparently automatically deep inside our ears.'
418
00:24:52,800 --> 00:24:55,760
The reason that we can hear so much and so well
419
00:24:55,760 --> 00:24:58,520
is that our ears are sophisticated detectors -
420
00:24:58,520 --> 00:25:02,000
a series of different structures all working together.
421
00:25:02,000 --> 00:25:05,040
If just one of the links in that chain is broken
422
00:25:05,040 --> 00:25:07,280
the consequences can be devastating.
423
00:25:15,280 --> 00:25:17,520
'I miss not hearing the birds.
424
00:25:20,520 --> 00:25:24,280
'I lost my hearing very, very quickly.
425
00:25:24,280 --> 00:25:26,640
'You can't believe it's happening.
426
00:25:29,040 --> 00:25:32,160
'You think, "Oh, did I hear something?"
427
00:25:33,160 --> 00:25:35,040
'But, no, you don't.
428
00:25:39,520 --> 00:25:42,800
'It really is frightening.'
429
00:25:49,520 --> 00:25:51,600
'This is Barbara.
430
00:25:51,600 --> 00:25:54,040
'She lives with her husband, Tony,
431
00:25:54,040 --> 00:25:57,200
'and they've been married for 53 years.'
432
00:25:57,200 --> 00:25:59,400
LAUGHTER
433
00:25:59,400 --> 00:26:01,280
- What's funny?
- Hm?
434
00:26:01,280 --> 00:26:02,760
What's funny?
435
00:26:02,760 --> 00:26:05,040
'But, for the past year and a half,
436
00:26:05,040 --> 00:26:07,760
'they've not been able to communicate properly.'
437
00:26:07,760 --> 00:26:10,520
Crashed on...the wires...!
438
00:26:12,520 --> 00:26:16,440
'Because, very suddenly, Barbara became profoundly deaf.'
439
00:26:18,520 --> 00:26:21,520
'I can't hear anything round out here.
440
00:26:21,520 --> 00:26:25,040
'I just miss my old life in general, really.
441
00:26:25,040 --> 00:26:26,560
'Yeah.'
442
00:26:26,560 --> 00:26:30,760
Not, sort of, hearing people or knowing what they're talking about.
443
00:26:30,760 --> 00:26:32,440
That's quite difficult.
444
00:26:32,440 --> 00:26:35,040
Deafness is a lonely world.
445
00:26:36,480 --> 00:26:41,280
'Barbara lost her hearing because just one small part of her ear
446
00:26:41,280 --> 00:26:43,080
'stopped working.
447
00:26:51,280 --> 00:26:55,280
'When sound enters a healthy ear, it gets funnelled through
448
00:26:55,280 --> 00:26:58,520
'to a coiled up structure called the cochlea -
449
00:26:58,520 --> 00:27:04,520
'a spiral-shaped cavity containing some 16,000 specialised cells
450
00:27:04,520 --> 00:27:06,280
'called hair cells.
451
00:27:07,280 --> 00:27:10,280
'As the sound wave moves through the cochlea,
452
00:27:10,280 --> 00:27:13,520
'the cells' hairlike protrusions are displaced...
453
00:27:15,520 --> 00:27:18,520
'..causing the cell to send electrical impulses
454
00:27:18,520 --> 00:27:22,520
'along nerve fibres that are destined for the brain.
455
00:27:26,760 --> 00:27:30,040
'But Barbara's hair cells are no longer working,
456
00:27:30,040 --> 00:27:33,520
'which means that although the rest of her ear is healthy,
457
00:27:33,520 --> 00:27:37,040
'her brain is completely starved of sound.'
458
00:27:39,040 --> 00:27:41,040
'I miss my independence.'
459
00:27:43,040 --> 00:27:48,160
What I try not to do is get down. I try to think positive.
460
00:27:51,600 --> 00:27:54,280
How are you feeling about today?
461
00:27:54,280 --> 00:27:56,760
- I'm OK. Yeah.
- OK?
462
00:27:56,760 --> 00:27:58,760
How about you?
463
00:27:58,760 --> 00:28:01,080
Bit nervous, I suppose.
464
00:28:01,080 --> 00:28:05,280
'A month ago, Barbara was fitted with a cochlear implant.
465
00:28:05,280 --> 00:28:09,320
'An array of electrodes has been threaded into her cochlea
466
00:28:09,320 --> 00:28:12,520
'that will take over the role of her faulty hair cells.
467
00:28:12,520 --> 00:28:15,280
'And today, at Southampton University,
468
00:28:15,280 --> 00:28:18,880
'it will be switched on and tested for the first time.
469
00:28:18,880 --> 00:28:21,760
So, I'm going to switch it on, OK?
470
00:28:25,680 --> 00:28:27,760
- Can you hear anything?
- Not yet, no.
471
00:28:27,760 --> 00:28:29,520
Just going to bring it up.
472
00:28:30,520 --> 00:28:31,960
Nothing.
473
00:28:39,480 --> 00:28:41,040
BEEPING
474
00:28:41,040 --> 00:28:43,040
Very faint.
475
00:28:43,040 --> 00:28:45,120
Very, very faint.
476
00:28:45,120 --> 00:28:46,920
BEEPING
477
00:28:46,920 --> 00:28:49,040
Very gradual, isn't it?
478
00:28:49,040 --> 00:28:50,760
Yeah. Bit more?
479
00:28:50,760 --> 00:28:52,240
Yes.
480
00:28:52,240 --> 00:28:55,040
I'm going to keep talking as I bring it up, OK?
481
00:28:55,040 --> 00:28:57,040
Just going to keep bringing it up.
482
00:28:57,040 --> 00:28:59,040
How did you get here today, Tony?
483
00:28:59,040 --> 00:29:01,880
I can hear... Can't understand.
484
00:29:01,880 --> 00:29:04,520
I can almost hear my own voice again!
485
00:29:06,280 --> 00:29:08,760
How's the volume now?
486
00:29:08,760 --> 00:29:11,040
How's the volume?
487
00:29:11,040 --> 00:29:13,520
- Yes!
- The volume?
488
00:29:13,520 --> 00:29:17,640
- The volume. How's the volume now, you said, yes.
- Yeah.
489
00:29:17,640 --> 00:29:19,520
What can you hear?
490
00:29:19,520 --> 00:29:22,520
- Can you hear me?
- Yes, I can hear you.
491
00:29:22,520 --> 00:29:23,960
Oh, dear.
492
00:29:23,960 --> 00:29:26,320
No, it's good.
493
00:29:26,320 --> 00:29:28,040
Yeah.
494
00:29:29,040 --> 00:29:31,280
'For the first time in over a year,
495
00:29:31,280 --> 00:29:35,040
'Barbara's brain is receiving sound signals.'
496
00:29:35,040 --> 00:29:37,040
- OK?
- That's amazing.
497
00:29:37,040 --> 00:29:40,040
When you take it off I can hear nothing.
498
00:29:42,120 --> 00:29:43,760
Amazing, yes.
499
00:29:43,760 --> 00:29:45,760
Don't make me cry!
500
00:29:48,040 --> 00:29:50,280
Don't worry about a hanky.
501
00:29:51,760 --> 00:29:54,760
- So, you're noticing the difference?
- It's incredible.
502
00:29:55,760 --> 00:29:58,280
Stop it. You're going to make me cry.
503
00:29:58,280 --> 00:30:00,000
Thank you.
504
00:30:01,000 --> 00:30:03,040
Oh, dear.
505
00:30:03,040 --> 00:30:05,280
I didn't think it would be this quick.
506
00:30:05,280 --> 00:30:07,280
No, you're doing really well.
507
00:30:07,280 --> 00:30:10,920
I thought for my birthday in July I might be able to hear then.
508
00:30:11,920 --> 00:30:15,280
What are we going to have for dinner tonight, some champagne?
509
00:30:15,280 --> 00:30:18,040
Stop it. You'll make me cry again!
510
00:30:26,280 --> 00:30:29,520
'Barbara is no longer lost in silence.
511
00:30:32,040 --> 00:30:35,520
'By translating sound into electrical signals,
512
00:30:35,520 --> 00:30:39,280
'the implant replicates the cochlea's key job,
513
00:30:39,280 --> 00:30:43,040
'returning Barbara to a world full of sound.
514
00:30:49,520 --> 00:30:52,520
'The cochlea is a truly extraordinary structure,
515
00:30:52,520 --> 00:30:56,040
'doing much more than simply translating noise.
516
00:30:56,040 --> 00:31:00,280
'It's also able to discriminate the incredible variation of sounds
517
00:31:00,280 --> 00:31:02,040
'in our environment.'
518
00:31:02,040 --> 00:31:05,040
Even though it's quite quiet and calm where I am now, there's still
519
00:31:05,040 --> 00:31:08,760
a huge richness of information in the sound around me.
520
00:31:08,760 --> 00:31:12,520
And a lot of that richness comes in the frequency of the sound,
521
00:31:12,520 --> 00:31:16,040
the number of times every second that air molecules are vibrating
522
00:31:16,040 --> 00:31:17,760
backwards and forwards.
523
00:31:17,760 --> 00:31:20,520
It could be a hundred times or a thousand times
524
00:31:20,520 --> 00:31:23,280
and they're all overlaid on top of each other.
525
00:31:23,280 --> 00:31:25,520
So, the singing birds and the distant road
526
00:31:25,520 --> 00:31:27,280
are all creating an environment
527
00:31:27,280 --> 00:31:29,280
that's full of different frequencies
528
00:31:29,280 --> 00:31:31,600
and that is really useful information.
529
00:31:40,080 --> 00:31:43,520
'Our cochlea has a really clever way of telling us
530
00:31:43,520 --> 00:31:46,520
'which frequencies are coming into the ear.
531
00:31:48,520 --> 00:31:51,520
'It exploits a phenomenon called resonance
532
00:31:51,520 --> 00:31:54,560
'which can be demonstrated with these conkers.'
533
00:31:55,560 --> 00:31:59,520
You can see if I push on one and I push on another one,
534
00:31:59,520 --> 00:32:03,200
this one with the short string is going backwards and forwards
535
00:32:03,200 --> 00:32:04,760
really quite quickly.
536
00:32:04,760 --> 00:32:07,280
Whereas this one down here with a longer string,
537
00:32:07,280 --> 00:32:11,000
you can see it swings much, much more slowly.
538
00:32:11,000 --> 00:32:14,520
Each one has its own natural frequency.
539
00:32:14,520 --> 00:32:16,520
And it's different for every conker
540
00:32:16,520 --> 00:32:18,760
because the string is a different length.
541
00:32:18,760 --> 00:32:22,160
Now, the clever bit comes when a frequency comes from somewhere else.
542
00:32:22,160 --> 00:32:24,760
And I'm going to demonstrate that here with this apple.
543
00:32:24,760 --> 00:32:27,520
If I swing the apple, what happens is that the apple
544
00:32:27,520 --> 00:32:31,280
will gently move the string and that's forcing all the conkers
545
00:32:31,280 --> 00:32:35,040
to oscillate at the same frequency as the apple,
546
00:32:35,040 --> 00:32:37,040
however longer their string is.
547
00:32:37,040 --> 00:32:40,040
And you can see that these ones are moving a little bit,
548
00:32:40,040 --> 00:32:42,760
moving a little bit, little bit more, and this one,
549
00:32:42,760 --> 00:32:45,280
this one is the one that's really responding.
550
00:32:45,280 --> 00:32:49,040
And if you look at it from this angle, you can see that this conker
551
00:32:49,040 --> 00:32:52,280
is the one that's got the same length of string as the apple.
552
00:32:52,280 --> 00:32:55,560
The others are hardly moving at all and this one is swinging loads.
553
00:32:55,560 --> 00:32:57,520
'And I can show you what happens
554
00:32:57,520 --> 00:33:00,800
'when I change the frequency of the driving force.
555
00:33:01,800 --> 00:33:05,400
'By shortening the string, I can make the apple swing faster.'
556
00:33:06,400 --> 00:33:09,520
We can see that this time it's this one.
557
00:33:09,520 --> 00:33:12,760
This conker is responding really, really strongly
558
00:33:12,760 --> 00:33:15,280
and this is the one again that's got more or less
559
00:33:15,280 --> 00:33:17,520
the same length of string as the apple.
560
00:33:17,520 --> 00:33:21,760
It's got the same natural frequency as the oscillation coming in.
561
00:33:22,960 --> 00:33:25,520
And now it's trying to hit me in the face!
562
00:33:26,920 --> 00:33:29,280
This is the phenomenon of resonance.
563
00:33:29,280 --> 00:33:32,320
This is very similar to what's happening in the cochlea.
564
00:33:36,040 --> 00:33:40,280
'Just as the conker strings have a variety of natural frequencies,
565
00:33:40,280 --> 00:33:43,240
'so do structures in the ear.
566
00:33:46,040 --> 00:33:50,280
'The thousands of tiny hair cells that send messages to the brain
567
00:33:50,280 --> 00:33:54,040
'sit along a structure called the basilar membrane.
568
00:33:54,040 --> 00:33:57,520
'This stretched piece of elastic that runs through the cochlea
569
00:33:57,520 --> 00:34:01,720
'has different natural frequencies as you go along it.
570
00:34:01,720 --> 00:34:04,040
It's got one end which is narrow and taut
571
00:34:04,040 --> 00:34:07,040
and it's got a very high natural frequency of oscillation
572
00:34:07,040 --> 00:34:11,040
and the other end of the basilar membrane is wider and less taut
573
00:34:11,040 --> 00:34:13,560
and that's got a lower frequency of oscillation.
574
00:34:14,640 --> 00:34:17,600
So, when sound comes into our ear,
575
00:34:17,600 --> 00:34:20,520
the whole basilar membrane will vibrate a little bit
576
00:34:20,520 --> 00:34:23,880
but one part of it will really start to vibrate.
577
00:34:23,880 --> 00:34:27,040
The one that matches the frequency of the sound coming in.
578
00:34:28,520 --> 00:34:32,520
And it's the hair cells at that part of the basilar membrane
579
00:34:32,520 --> 00:34:36,280
that are stimulated, that send the sound into our brains
580
00:34:36,280 --> 00:34:40,040
and that's how our ears tell us which frequencies of sound
581
00:34:40,040 --> 00:34:42,760
are coming in from the environment around us.
582
00:34:45,880 --> 00:34:50,520
'This elegant and simple mechanism gives us the ability to detect
583
00:34:50,520 --> 00:34:54,520
'and interpret an enormous range of frequencies.
584
00:34:54,520 --> 00:34:58,760
'A far greater range of sounds than the spectrum of light waves
585
00:34:58,760 --> 00:35:00,880
'we can see with our eyes.
586
00:35:04,240 --> 00:35:09,040
'From low-sounding noises that go through 20 cycles a second
587
00:35:09,040 --> 00:35:13,360
'and have wavelengths 17 metres long.
588
00:35:17,040 --> 00:35:20,200
'All the way through to very high-frequency sounds
589
00:35:20,200 --> 00:35:24,280
'that can exceed 18,000 cycles a second
590
00:35:24,280 --> 00:35:28,240
'and have a wavelength of under two centimetres.
591
00:35:31,520 --> 00:35:34,040
'The cochlea's a sophisticated structure
592
00:35:34,040 --> 00:35:37,040
'that lets us detect a huge variety of sounds.
593
00:35:37,040 --> 00:35:40,760
This story is interesting because it passed through
594
00:35:40,760 --> 00:35:45,040
one of the most significant stages in evolutionary history.
595
00:35:45,040 --> 00:35:50,520
When hearing and life first evolved, it all happened underwater.
596
00:35:51,640 --> 00:35:55,760
'Which would mean that, one day, it would have to confront and overcome
597
00:35:55,760 --> 00:35:57,640
'a physical law of nature.
598
00:36:02,760 --> 00:36:07,480
'3.5 billion years ago, life began in the oceans.
599
00:36:10,160 --> 00:36:13,760
'And as organisms became ever more complex,
600
00:36:13,760 --> 00:36:17,520
'they developed increasingly sophisticated senses.
601
00:36:22,280 --> 00:36:25,280
'Around 400 million years ago,
602
00:36:25,280 --> 00:36:28,760
'fish became the first hearing animal,
603
00:36:28,760 --> 00:36:30,760
'evolving structures that,
604
00:36:30,760 --> 00:36:33,360
'although much simpler than the modern cochlea,
605
00:36:33,360 --> 00:36:35,520
'worked in a similar way.'
606
00:36:37,200 --> 00:36:40,520
Ears underwater were fluid-filled cavities
607
00:36:40,520 --> 00:36:44,040
and so sound could easily travel from the water
608
00:36:44,040 --> 00:36:47,040
into the underwater ear and it could easily be detected
609
00:36:47,040 --> 00:36:50,120
because there was liquid on both sides of that boundary.
610
00:36:52,800 --> 00:36:55,520
'But when that life came up into air,
611
00:36:55,520 --> 00:36:57,520
'suddenly the sound was in the air
612
00:36:57,520 --> 00:36:59,840
'but the ear was still filled with fluid
613
00:36:59,840 --> 00:37:01,720
'and that was a problem.'
614
00:37:07,760 --> 00:37:11,040
I've got a set up here that will show what happens when sound
615
00:37:11,040 --> 00:37:15,040
tries to travel across a boundary from air into water.
616
00:37:15,040 --> 00:37:18,520
I've got two microphones here. One's a normal microphone. This one.
617
00:37:18,520 --> 00:37:21,040
It's set up for hearing sound in air.
618
00:37:21,040 --> 00:37:25,040
And the other one is set up for hearing sound underwater, down here.
619
00:37:25,040 --> 00:37:27,040
That's called a hydrophone.
620
00:37:27,040 --> 00:37:29,760
I've got some tent pegs here.
621
00:37:29,760 --> 00:37:33,040
I could hear that quite easily and so could the microphone,
622
00:37:33,040 --> 00:37:36,040
so there's a great big spike on the microphone in air.
623
00:37:36,040 --> 00:37:39,280
But the hydrophone in water heard almost nothing.
624
00:37:39,280 --> 00:37:41,520
What's going on is that at the boundary,
625
00:37:41,520 --> 00:37:44,280
when there's air up here and water down here,
626
00:37:44,280 --> 00:37:47,280
and sound comes from the air and hits that boundary,
627
00:37:47,280 --> 00:37:51,520
because air is less dense and much easier to squash than water,
628
00:37:51,520 --> 00:37:53,520
instead of travelling through,
629
00:37:53,520 --> 00:37:55,760
that sound wave just bounces straight off.
630
00:37:55,760 --> 00:37:58,040
It doesn't get through the boundary.
631
00:38:07,680 --> 00:38:10,280
And this is the problem that early life faced.
632
00:38:10,280 --> 00:38:13,040
If you've got a fluid-filled ear, liquid-filled ear,
633
00:38:13,040 --> 00:38:15,760
it works perfectly underwater because sound can travel
634
00:38:15,760 --> 00:38:18,280
through the water into your liquid-filled ear
635
00:38:18,280 --> 00:38:21,240
and you can hear the sound. But once you put that in air,
636
00:38:21,240 --> 00:38:23,280
the sound comes in from the air
637
00:38:23,280 --> 00:38:26,040
but it hits your ear and bounces straight off.
638
00:38:26,040 --> 00:38:28,040
It can't get in to be detected.
639
00:38:29,520 --> 00:38:33,640
'The way sound behaves at a boundary between two mediums
640
00:38:33,640 --> 00:38:38,560
'hindered the ability of early land-based life to hear properly.
641
00:38:41,040 --> 00:38:44,280
The process of evolution came up with a really elegant solution
642
00:38:44,280 --> 00:38:48,040
to this problem, by moving around some very tiny bones.
643
00:38:48,040 --> 00:38:51,280
And here they are. These are life-size casts of them.
644
00:38:51,280 --> 00:38:54,920
And they're called the malleus, the incus and the stapes.
645
00:38:54,920 --> 00:38:57,720
The ossicles, which means "tiny bones".
646
00:38:57,720 --> 00:39:00,040
And they are the smallest bones in the body.
647
00:39:00,040 --> 00:39:03,280
And two of them were part of the jawbone in our marine ancestors
648
00:39:03,280 --> 00:39:06,520
but they moved into the middle ear and they do something very clever.
649
00:39:06,520 --> 00:39:08,280
By working together,
650
00:39:08,280 --> 00:39:12,960
they help move sound from the outside world into the cochlea.
651
00:39:21,880 --> 00:39:24,760
'The ossicles sit just in front of the cochlea.
652
00:39:26,760 --> 00:39:31,760
'And when sound hits the eardrum, these tiny bones are set in motion.
653
00:39:33,280 --> 00:39:36,280
'Moving efficiently as a set of levers
654
00:39:36,280 --> 00:39:40,280
'between the large eardrum and the tiny stapes.
655
00:39:43,040 --> 00:39:47,040
'This increases the energy that's transferred to the cochlea.
656
00:39:51,280 --> 00:39:54,280
'This sophisticated little mechanism acts as an amplifier
657
00:39:54,280 --> 00:39:55,920
'and it's really efficient.'
658
00:39:55,920 --> 00:39:58,520
What matters is the amount of sound energy
659
00:39:58,520 --> 00:40:01,040
that gets into the fluid inside the cochlea.
660
00:40:01,040 --> 00:40:03,520
And without this, it would be about 1%,
661
00:40:03,520 --> 00:40:07,040
but with a middle ear like this, it's about 60%.
662
00:40:07,040 --> 00:40:10,040
So, this is the crucial evolutionary step
663
00:40:10,040 --> 00:40:13,760
that allowed land-based mammals to develop such good hearing.
664
00:40:16,760 --> 00:40:21,160
'Hearing that allows us to detect a huge range of amplitudes.
665
00:40:22,160 --> 00:40:25,160
'Everything from the thundering roar of an engine...
666
00:40:27,160 --> 00:40:30,520
'..to the flapping of an insect's wings.
667
00:40:32,520 --> 00:40:35,760
'And hearing the very quiet end of this range
668
00:40:35,760 --> 00:40:41,280
'doesn't rely solely on the ear but also on what lies beyond it.
669
00:40:45,280 --> 00:40:50,280
'To experience this, I need to find something extremely rare.
670
00:40:50,280 --> 00:40:52,040
'Silence.
671
00:40:53,520 --> 00:40:56,280
'It doesn't exist in the natural world
672
00:40:56,280 --> 00:41:00,320
'so I've come here - the largest anechoic chamber in Britain.
673
00:41:03,520 --> 00:41:08,520
'It's been meticulously engineered to be incredibly quiet.
674
00:41:08,520 --> 00:41:12,120
'And it's here that I'll test my ears to their limit.'
675
00:41:18,520 --> 00:41:21,520
The idea of all this clobber is that I have to be in there
676
00:41:21,520 --> 00:41:23,280
completely on my own.
677
00:41:23,280 --> 00:41:26,120
So, there's no sources of sound and nothing to reflect off.
678
00:41:29,040 --> 00:41:32,040
So, this might be a moot point because I might decide I hate it
679
00:41:32,040 --> 00:41:34,040
after two minutes and that's all right.
680
00:41:34,040 --> 00:41:37,400
But if I'm all right after 20 minutes, is there any reason to...
681
00:41:37,400 --> 00:41:40,520
Does it get worse as you go? Because some people don't seem to mind it.
682
00:41:40,520 --> 00:41:43,760
I think it's completely individual and so you, kind of, see how it is.
683
00:42:05,120 --> 00:42:10,040
'All on my own, I can feel myself adjusting to this new environment.
684
00:42:12,040 --> 00:42:15,240
'I can't hear any sounds from outside.
685
00:42:16,240 --> 00:42:18,720
'It's the quietest place I've ever been.
686
00:42:25,760 --> 00:42:31,040
'And as I sit, the rustle of my clothes sounds strangely loud.
687
00:42:32,040 --> 00:42:34,080
HEART BEATING
688
00:42:36,040 --> 00:42:39,520
'I'm starting to notice the sounds of my own body.
689
00:42:42,040 --> 00:42:44,520
'The regular beating of my heart.
690
00:42:46,520 --> 00:42:50,520
'A background hiss, perhaps from the firing of my nerves.
691
00:42:54,520 --> 00:42:56,760
'The soft whisper of my breath.
692
00:43:00,520 --> 00:43:04,760
'Sounds that I don't ordinarily hear have now become dominant.'
693
00:43:17,480 --> 00:43:20,320
Oh, they're opening the door.
694
00:43:20,320 --> 00:43:23,040
I wonder what the outside world's going to be like now.
695
00:43:24,040 --> 00:43:28,480
'After 50 minutes, Dr Peter Keating arrives to explain
696
00:43:28,480 --> 00:43:32,040
'how I could hear so much in a place like this.
697
00:43:33,040 --> 00:43:36,040
- So, how was that?
- It wasn't ever completely silent.
698
00:43:36,040 --> 00:43:38,760
My brain was always telling me it was hearing something
699
00:43:38,760 --> 00:43:40,680
but that something was very, very quiet.
700
00:43:40,680 --> 00:43:43,760
When you take external sounds away, which is what's happening here,
701
00:43:43,760 --> 00:43:46,520
then first of all you become more sensitive to the sounds
702
00:43:46,520 --> 00:43:48,040
that are inside your body.
703
00:43:48,040 --> 00:43:51,280
There's actually a little separate set of cells in your auditory nerve
704
00:43:51,280 --> 00:43:53,760
which are responsible for hearing very quiet sounds.
705
00:43:53,760 --> 00:43:56,760
So, in here, you were probably switching over to using those.
706
00:43:59,040 --> 00:44:01,280
'A specialised type of nerve fibre
707
00:44:01,280 --> 00:44:06,000
'carries very quiet sound signals from the cochlea to the brain,
708
00:44:06,000 --> 00:44:10,040
'where our sensitivity to this type of sound isn't fixed.
709
00:44:11,040 --> 00:44:13,040
The brain is constantly adapting,
710
00:44:13,040 --> 00:44:16,520
and so, if you take away loud sounds and you only have quiet sounds,
711
00:44:16,520 --> 00:44:19,040
the brain will get used to that over time.
712
00:44:19,040 --> 00:44:22,040
So, the physical hearing apparatus is staying the same
713
00:44:22,040 --> 00:44:25,440
- but our brains are what's doing the adapting?
- Absolutely.
714
00:44:25,440 --> 00:44:28,280
So, when you came in here, in the first seconds to minutes,
715
00:44:28,280 --> 00:44:31,040
there would have been some changes going on in your brain.
716
00:44:31,040 --> 00:44:34,280
If you'd stayed in here for longer, if you'd stayed in for days, weeks,
717
00:44:34,280 --> 00:44:36,280
more changes would have happened.
718
00:44:36,280 --> 00:44:37,840
And if you'd stayed in here for months,
719
00:44:37,840 --> 00:44:39,520
even more changes would have happened.
720
00:44:39,520 --> 00:44:42,280
That's one of the things that we're finding out about the brain
721
00:44:42,280 --> 00:44:45,040
is that you can adapt to these changes in sensory input.
722
00:44:45,040 --> 00:44:48,280
Not just hearing, but in vision and all kinds of other sensory systems.
723
00:44:48,280 --> 00:44:51,040
And these can happen at all kinds of different timescales.
724
00:44:52,040 --> 00:44:54,040
'The processing power of our brain,
725
00:44:54,040 --> 00:44:56,280
'together with the mechanics of our ears,
726
00:44:56,280 --> 00:44:59,520
'forms an incredibly powerful and adaptive system
727
00:44:59,520 --> 00:45:01,760
'to listen in to the world.
728
00:45:22,760 --> 00:45:25,280
Understanding the physical properties of sound
729
00:45:25,280 --> 00:45:29,040
and being able to decipher them to learn about the world around us
730
00:45:29,040 --> 00:45:31,040
is a really powerful tool.
731
00:45:31,040 --> 00:45:33,520
But we're not limited to just listening in
732
00:45:33,520 --> 00:45:36,040
on what the environment sends to us.
733
00:45:36,040 --> 00:45:41,040
We can create our own sound to send it out to probe the world.
734
00:45:41,040 --> 00:45:44,280
And that can teach us about ourselves, our planet
735
00:45:44,280 --> 00:45:46,520
and even what's beyond that.
736
00:45:56,800 --> 00:46:01,160
'Sound has been especially useful in looking at things we can't see.
737
00:46:01,160 --> 00:46:04,280
'Things that are hidden from the world of light.
738
00:46:07,880 --> 00:46:10,760
'It began in the early years of the First World War,
739
00:46:10,760 --> 00:46:13,920
'when submarines became a deadly weapon.'
740
00:46:18,720 --> 00:46:20,840
EXPLOSION
741
00:46:20,840 --> 00:46:22,520
'Almost invisible,
742
00:46:22,520 --> 00:46:25,040
'these machines would drive the Allies
743
00:46:25,040 --> 00:46:27,600
'to develop new detection technology.
744
00:46:30,120 --> 00:46:34,800
'Sound can travel exceptionally long distances underwater
745
00:46:34,800 --> 00:46:39,760
'and so acoustic echo ranging, or sonar, offered an obvious solution.
746
00:46:42,240 --> 00:46:45,280
'And after the Second World War had come to an end,
747
00:46:45,280 --> 00:46:48,880
'the rapid advancements of underwater acoustics continued.
748
00:46:51,040 --> 00:46:54,280
'Our relationship with the oceans can be limited.
749
00:46:54,280 --> 00:46:57,520
'Quite often you look out over the sea and what you see is this.
750
00:46:57,520 --> 00:47:01,040
'It's grey and opaque, you can't see through the surface.
751
00:47:01,040 --> 00:47:02,920
'It looks a little bit dull.'
752
00:47:03,920 --> 00:47:07,280
But underwater acoustics changed all of that.
753
00:47:07,280 --> 00:47:10,520
Once you can use sound to explore the underwater world,
754
00:47:10,520 --> 00:47:13,200
you're not limited to looking for submarines.
755
00:47:14,200 --> 00:47:17,520
'Today, even as we reach for the stars,
756
00:47:17,520 --> 00:47:22,040
'we know less about this ocean than we do the surface of the moon.'
757
00:47:22,040 --> 00:47:25,040
'By the 1950s, oceanographers across the world
758
00:47:25,040 --> 00:47:27,520
'were using military sonar technology
759
00:47:27,520 --> 00:47:30,760
'to look down at the deep ocean floor,
760
00:47:30,760 --> 00:47:33,800
'which, for centuries, we could only imagine.
761
00:47:36,000 --> 00:47:39,520
'They discovered an extraordinary underwater landscape
762
00:47:39,520 --> 00:47:42,760
'of towering mountains and deep trenches.
763
00:47:45,280 --> 00:47:48,520
'Sound played a key role in understanding
764
00:47:48,520 --> 00:47:51,560
'the magnificent structures of our world.'
765
00:47:51,560 --> 00:47:55,520
The oceans are one of the most important features of our planet
766
00:47:55,520 --> 00:47:59,280
and they're not just the filler between the interesting bits.
767
00:47:59,280 --> 00:48:01,280
Once you can see them properly,
768
00:48:01,280 --> 00:48:04,040
you can see the oceans become a place.
769
00:48:10,520 --> 00:48:14,040
'Today, sonar doesn't just show us large-scale structures,
770
00:48:14,040 --> 00:48:17,280
'it can also reveal exquisite detail.'
771
00:48:17,280 --> 00:48:19,440
- Welcome aboard.
- Thank you.
772
00:48:19,440 --> 00:48:23,920
'Which, until recently, had been a job only our eyes could perform.
773
00:48:24,920 --> 00:48:28,520
'This is the North Sea, off the coast of Suffolk.'
774
00:48:30,040 --> 00:48:33,040
Looks just like an ordinary bit of ocean
775
00:48:33,040 --> 00:48:36,760
but there is an archaeological site down there,
776
00:48:36,760 --> 00:48:38,760
so I'm going down to have a look.
777
00:48:38,760 --> 00:48:41,040
I have a lot of layers to put on.
778
00:48:42,040 --> 00:48:43,760
Oops. The other way round.
779
00:48:54,760 --> 00:48:58,040
Right, it's definitely cold in the North Sea!
780
00:48:58,040 --> 00:49:00,520
- I can't actually see you.
- You can't see me at all?
781
00:49:00,520 --> 00:49:04,040
- Unless you come in really close.
- So...
- Yeah, it's just so brown.
782
00:49:04,040 --> 00:49:06,480
I've got my glove here.
783
00:49:06,480 --> 00:49:11,040
And if I hold that out, in front of my face underwater, you can't
784
00:49:11,040 --> 00:49:14,520
see anything, so I can't see this far in front of my face.
785
00:49:14,520 --> 00:49:18,760
And the reason it's this brown, horrible colour,
786
00:49:18,760 --> 00:49:21,520
is that the water is clearly full of sediment.
787
00:49:21,520 --> 00:49:25,280
There's tiny little particles of silt and sand.
788
00:49:25,280 --> 00:49:27,760
And so seeing anything...
789
00:49:27,760 --> 00:49:29,840
is virtually impossible.
790
00:49:33,760 --> 00:49:35,760
'Even though we're near the coast,
791
00:49:35,760 --> 00:49:38,280
'where the water isn't particularly deep,
792
00:49:38,280 --> 00:49:40,960
'the visibility is still appalling.'
793
00:49:44,040 --> 00:49:46,760
That's... That's terrifying.
794
00:49:47,760 --> 00:49:52,040
I was only going down a metre or two and it's completely black.
795
00:49:52,040 --> 00:49:54,600
Like, absolutely dark.
796
00:49:54,600 --> 00:49:57,960
'Since I couldn't see anything for myself,
797
00:49:57,960 --> 00:50:01,760
'Professor David Sear explains what lies beneath us.'
798
00:50:01,760 --> 00:50:05,040
When I was down there a little while ago I couldn't see anything.
799
00:50:05,040 --> 00:50:06,760
So, what is down there?
800
00:50:06,760 --> 00:50:10,920
Well, actually, down there is one of the largest archaeological sites
801
00:50:10,920 --> 00:50:12,760
in the world, called Dunwich.
802
00:50:12,760 --> 00:50:15,040
Dunwich, to a lot of people, is just a small village.
803
00:50:15,040 --> 00:50:18,280
800 years ago it was the sixth largest international port
804
00:50:18,280 --> 00:50:19,840
in the North Sea.
805
00:50:19,840 --> 00:50:23,040
And the story of Dunwich is one of coastal erosion.
806
00:50:23,040 --> 00:50:27,160
Coastal erosion driven by a series of very large storms.
807
00:50:27,160 --> 00:50:29,520
So, this sounds like the perfect job for sonar.
808
00:50:29,520 --> 00:50:31,520
What do you see when you look with sonar?
809
00:50:31,520 --> 00:50:34,040
Sonar enabled us to cover a large area
810
00:50:34,040 --> 00:50:37,040
and we were able to see that there were indeed structures.
811
00:50:37,040 --> 00:50:40,280
The important thing was that we didn't know whether they were
812
00:50:40,280 --> 00:50:44,000
geology or were they actually parts of churches and buildings?
813
00:50:44,000 --> 00:50:46,520
So, what you ideally need is a technology
814
00:50:46,520 --> 00:50:49,760
that is able to see through this turbid, muddy water
815
00:50:49,760 --> 00:50:53,280
with the detail to enable you to see individual,
816
00:50:53,280 --> 00:50:57,480
say, carved blocks or other evidence of it being made by people.
817
00:50:57,480 --> 00:51:00,520
We came across a technology that is relatively new
818
00:51:00,520 --> 00:51:02,080
and it does just that.
819
00:51:04,280 --> 00:51:08,760
It uses sound to project... A bit like a torch beam, but sound.
820
00:51:08,760 --> 00:51:11,040
And you don't do that from a boat?
821
00:51:11,040 --> 00:51:13,520
You don't. You have to send a diver down
822
00:51:13,520 --> 00:51:18,040
and that diver sees what the sound is illuminating, if you like,
823
00:51:18,040 --> 00:51:19,760
in their visor.
824
00:51:26,040 --> 00:51:28,760
'Sound waves from surface-based sonar
825
00:51:28,760 --> 00:51:32,280
'can travel easily through the water, which provided David
826
00:51:32,280 --> 00:51:34,760
'with the layout and general structure
827
00:51:34,760 --> 00:51:37,200
'of this two-kilometre-squared site.
828
00:51:38,200 --> 00:51:41,040
'Yet it was the much higher frequency sound waves
829
00:51:41,040 --> 00:51:45,520
'from the sonar camera that gave David what he really needed.
830
00:51:45,520 --> 00:51:48,280
'Although these sound waves can't travel as far,
831
00:51:48,280 --> 00:51:51,760
'they can create much more detailed images,
832
00:51:51,760 --> 00:51:54,520
'and showed that what lay beneath the waves
833
00:51:54,520 --> 00:51:57,520
'were structures with sharp straight edges.
834
00:51:58,520 --> 00:52:01,520
'Edges that could only have been made by man.'
835
00:52:09,280 --> 00:52:11,520
The first time we saw this imagery,
836
00:52:11,520 --> 00:52:15,280
looking at it in real-time as the diver saw it, it was fantastic,
837
00:52:15,280 --> 00:52:19,280
because you could see great blocks of masonry, made of flints,
838
00:52:19,280 --> 00:52:23,040
rubble, mortar, just like the churches today on land.
839
00:52:23,040 --> 00:52:25,000
You see it on the seabed.
840
00:52:25,000 --> 00:52:28,040
That nailed it for us. It was the evidence we needed
841
00:52:28,040 --> 00:52:31,280
to move from the historical accounts to the reality of,
842
00:52:31,280 --> 00:52:34,480
yes, these are the ruins of churches from medieval Dunwich.
843
00:52:34,480 --> 00:52:37,280
'Sending sound waves through the ocean
844
00:52:37,280 --> 00:52:39,760
'has unlocked marine archaeology,
845
00:52:39,760 --> 00:52:43,560
'uncovering the human stories hidden beneath the sea.
846
00:52:50,280 --> 00:52:54,040
'We're continually getting better at detecting and controlling
847
00:52:54,040 --> 00:52:56,280
'the nuances of sound waves
848
00:52:56,280 --> 00:53:00,280
'and at using them as tools for probing and manipulating our world.
849
00:53:01,280 --> 00:53:04,280
'But there are other worlds out there.
850
00:53:05,280 --> 00:53:08,520
'Even though sound can't travel across the solar system,
851
00:53:08,520 --> 00:53:12,040
'every planet and moon is like a little bubble of sound
852
00:53:12,040 --> 00:53:15,040
'isolated from us by the vacuum of space.
853
00:53:16,040 --> 00:53:19,760
'And there's a huge amount to learn from those little bubbles of sound,
854
00:53:19,760 --> 00:53:22,040
'if only we can listen in.'
855
00:53:23,280 --> 00:53:26,360
'Three, two, one...
856
00:53:26,360 --> 00:53:29,960
'And lift-off of the Cassini spacecraft!'
857
00:53:29,960 --> 00:53:33,680
'In 1997, one of the largest spacecraft ever launched
858
00:53:33,680 --> 00:53:37,040
'started its billion-kilometre journey.'
859
00:53:38,040 --> 00:53:40,040
'We have cleared the tower
860
00:53:40,040 --> 00:53:43,280
'and the Cassini spacecraft is on its way to Saturn.'
861
00:53:47,760 --> 00:53:52,760
'In 2005, Cassini sent a probe called Huygens to Titan,
862
00:53:52,760 --> 00:53:55,280
'the largest of Saturn's moons,
863
00:53:59,520 --> 00:54:04,360
'A world shrouded by a thick, opaque atmosphere...
864
00:54:06,640 --> 00:54:10,520
'..making it almost impossible to explore from a distance.
865
00:54:13,040 --> 00:54:17,040
'So, for decades, this moon remained much of a mystery.'
866
00:54:20,920 --> 00:54:24,280
Huygens is still the only probe to have successfully landed
867
00:54:24,280 --> 00:54:26,280
in the outer solar system.
868
00:54:26,280 --> 00:54:30,520
And as it deployed its parachutes and started this two-and-a-half-hour
869
00:54:30,520 --> 00:54:34,680
drift down through the atmosphere of Titan towards the surface,
870
00:54:34,680 --> 00:54:38,040
there was a suite of instruments on the probe measuring all sorts
871
00:54:38,040 --> 00:54:40,760
of things about the environment and the conditions.
872
00:54:40,760 --> 00:54:44,000
And some of those instruments were recording sound.
873
00:54:46,760 --> 00:54:51,040
'Around 160km above the surface of Titan,
874
00:54:51,040 --> 00:54:54,040
'Huygens deployed a microphone,
875
00:54:54,040 --> 00:54:57,840
'which recorded the sounds of Titan's atmosphere.
876
00:55:02,760 --> 00:55:05,040
SOUND OF STRONG WIND
877
00:55:11,040 --> 00:55:12,760
And this is it.
878
00:55:12,760 --> 00:55:15,520
This is what the microphone on Huygens heard
879
00:55:15,520 --> 00:55:18,040
as it fell through Titan's atmosphere.
880
00:55:19,520 --> 00:55:23,760
What you're hearing is the roaring of the wind going past the probe
881
00:55:23,760 --> 00:55:27,040
and the probe falling down through the atmosphere.
882
00:55:27,040 --> 00:55:32,400
This is the sound of an alien world, and this was only the start.
883
00:55:37,520 --> 00:55:41,280
'Another instrument used sonar to detect the surface
884
00:55:41,280 --> 00:55:44,280
'during the final 90 metres of the descent.
885
00:55:44,280 --> 00:55:48,040
'It showed that Titan's terrain rises and falls.
886
00:55:49,040 --> 00:55:52,040
'That the surface is relatively smooth,
887
00:55:52,040 --> 00:55:54,160
'not dissimilar to gravel,
888
00:55:54,160 --> 00:55:57,280
'and that this surface is likely to be damp.'
889
00:55:58,760 --> 00:56:01,920
This is the landscape that Huygens landed on.
890
00:56:01,920 --> 00:56:05,040
Sonar was one of the tools that helps us understand it.
891
00:56:06,040 --> 00:56:09,040
Even if a planet or a moon hasn't got an atmosphere,
892
00:56:09,040 --> 00:56:12,280
sound can still be generated and transmitted through its liquid
893
00:56:12,280 --> 00:56:16,040
and solid layers, so potentially, if you sent an acoustic probe
894
00:56:16,040 --> 00:56:20,040
to another world, you might hear the sound of thunder,
895
00:56:20,040 --> 00:56:22,040
or hear meteorite strikes,
896
00:56:22,040 --> 00:56:25,040
or the flow of rivers. Perhaps rivers of methane.
897
00:56:25,040 --> 00:56:27,040
Or the sound of rain.
898
00:56:27,040 --> 00:56:30,520
And as more and more missions are sent out into the solar system
899
00:56:30,520 --> 00:56:34,520
to explore, acoustic probes are going to become more and more common
900
00:56:34,520 --> 00:56:38,640
as a way of exploring not just our world but others.
901
00:57:03,520 --> 00:57:07,040
'We live in a dynamic, pulsating world of sound
902
00:57:07,040 --> 00:57:10,920
'and it touches our skin and our clothes and our lives every day.'
903
00:57:10,920 --> 00:57:14,520
We can only tap into it because we have these two complex,
904
00:57:14,520 --> 00:57:17,760
sensitive detectors on either side of our head,
905
00:57:17,760 --> 00:57:20,360
but that's enough to sense the riches.
906
00:57:26,040 --> 00:57:28,880
Sound is so important for our species.
907
00:57:28,880 --> 00:57:31,040
It's deeply embedded in our culture
908
00:57:31,040 --> 00:57:34,280
and it's allowing us to push our technological boundaries
909
00:57:34,280 --> 00:57:36,480
to better understand our world.
910
00:57:36,480 --> 00:57:40,280
And the best thing about it is that that world of sound is right here.
911
00:57:40,280 --> 00:57:42,800
All you have to do is listen.
912
00:57:42,800 --> 00:57:45,840
FIREWORKS
913
00:57:52,240 --> 00:57:55,640
If you'd like to find out more about the science of sound
914
00:57:55,640 --> 00:57:59,040
and how we hear sound, go to the BBC website on screen
915
00:57:59,040 --> 00:58:02,000
and follow the links to the Open University.
78018
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