Today, we're going to do an experiment together.
I'm super excited for it because I was really surprised by the results.
"You were completely wrong"
You're going to need one thing for the experiment but it's absolutely crucial you use it,
and that's headphones.
So pause the video and put them on.
If you've put them on the right way around, you should hear this in your right ear
and this in your left ear.
Ready? Let's do it!
To give you a taste of the experiment we're about to conduct, here is a snippet
that will immerse you in a fishing day.
Listen hard.
You must have heard sounds of the mill on the one side, and sounds of the cutting
of the fish on the other side; you could locate the area of origin of the sounds.
That's thanks to a so-called binaural recording that attempts to recreate the way that
we perceive sounds with our two ears, by using two regular microphones...
with a twist.
The microphones have fake ears stuck on them.
The point of this kind of recording is to immerse the public into a scene
to allow for them to experience, say, a day of fishing, as if they were really there.
You may already know this kind of recording, but what we're going to do today
is test its limits.
Franck and I met up with Régis, a postdoc researcher at Brams,
the international research lab on brains, music and sound.
He helped us use their binaural recording system that's strapped onto a mannequin.
Are you ready?
Yep
Now listen.
You could have kept your eyes closed and still known where the sound came from.
Let's put that to the test.
I'm going to need you to participate.
What if I play this sound for you?
Can you tell where it's coming from?
I'll play it again.
How about this one?
You should have heard the first sound in your left ear and the second
in your right ear.
Telling the difference between sounds coming from the right or left comes very easily to us.
Let's keep going.
This sound came from in front of you.
Front, middle.
Next try.
You must have noticed that this sound came from your right,
but from a lower point to your right.
Right, bottom.
Next test.
It came from somewhere high behind you.
Behind, top.
Next test.
This one came from the low left, or was it high left?
Or middle?
Personally, I can't tell the difference between different heights
or if the sound comes from in front or behind me.
This should be the case for you, too, at least I hope so, so let me know
in the comments.
This limitation is directly linked to the way that we locate sounds.
We use 3 localization mechanisms that complete one another:
The first is sound intensity.
Also known as the difference in intensity between the two ears; a sound coming from the left
is perceived louder by the left ear than it is by the right, since the head functions as a screen
that blocks sound waves.
The second is time difference.
When a sound is produced on one side of your head, it will take longer to reach
the other ear because it has a longer distance to travel.
This difference in time allows us to locate whether the sound is coming from our left or our right.
These two mechanisms are called binaural cues and the brain processes them
to interpret where sounds come from.
The brain is really doing all the work here.
In these cases, the binaural recording is highly efficient.
The last mechanism is one that gives us information about the vertical location
of sounds, differences between high and low as well as front or back.
In order to make such distinctions, the shape of our ears
and the presence of our head and torso are the main reasons we manage to locate sounds.
Those are called spectral cues.
Let me explain.
Sound waves, wherever they come from, will hit the shapes in our ears
in a different way if they come from above or below us.
The shape of our ears, our height etc. act like filters that physically modify the sound
(both its frequency and its spectrum).
Once such modifications have been made,
the sound enters the auditory tube and allows us to figure out
where it is coming from.
So how come our audio recordings, which we did using fake ears,
doesn't allow us to tell if a sound comes from above, below, behind or at the front?
That's the limit of binaural audio.
We all have different ears.
One person will have a completely different auricle
(that's what they're called)
from another.
While the overall shape is similar, if you look closely at the angles, the width
and so on, you'll spot differences.
That means that in order for you to know where the sounds really come from,
you'd need for the ear used during audio recordings
to be exactly the same as yours.
The one we have here is your 'average' ear, it doesn't model anybody's ear perfectly.
Let's do another experiment.
I'd really, really like you to try this one at home because it's really confusing
and all you need is some modeling clay.
This will help us demonstrate the importance of the ear's shape
in locating sounds.
Are you ready?
Yes
Franck, even blindfoled, manages to locate sounds perfectly.
Alright, I think we're good.
Did I get it right?
Yeah, completely right.
But after slightly altering the shape of his ear with modeling clay
(I really recommend you try it too), he wasn't as successful.
It's hard to tell because you've done both very well and very poorly.
I was back there and you pointed to up here.
Were you really there? I really thought you were over here.
That being said, one surprising thing that Régis told us
is that if we keep the modeling clay in for a few weeks we'll end up being able to
once again locate sounds around us because our brain
will have adapted to the change,
as long as it isn't too drastic.
Even though binaural recordings are limited, when you immerse yourself in a video,
it doesn't feel like you're missing a spatial dimension.
I think that that is thanks to our eyes that do a bit of extra work
to complete our hearing and recreate a sort of spatial map for sounds.
Binaraul recordings as we've experienced in this video
isn't so far off from regular stereo.
In order to fix its defects, the technology is evolving towards so-called
ambisonic reproduction systems that use even more microphones and in my opinion,
we're going to hear about those for a few more years.
So if you are to completely immerse yourself into an audio environment using only headphones,
you'll need for all the sounds to have been recorded through your ears,
or at least a copy of your ears,
to make it less inconvenient.
Or you could always trade your headphones for a bigger sound system
like the one in this lab which contains over 80 speakers.
I hope you liked this video and that you now want to try the experiment with the modeling clay
it's worth trying it with friends, family, kids...
at least I've had a lot of fun with it.
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