00:00So, you're at a festival and it's getting really rowdy.
00:04Your friend has gone to grab some drinks, and you've lost sight of him.
00:07Suddenly, his voice sounds loud and clear in your ears, asking what drink he should get for you.
00:13Now, are we in a sci-fi movie or what?
00:17No, apparently that's what scientists can do now.
00:20They've made a sound that can travel through space and reach just your ears in the crowd.
00:26Researchers conducted a new study and found a way to make tiny pockets of sound stay in one place.
00:33These pockets don't spread around like normal sound, and it means we can now create sound exactly where we want it,
00:40like sending it only to one person in a room.
00:44This discovery might totally change the way we enjoy music, talk to people, or experience sound in games and virtual spaces.
00:51You see, sound is just vibration moving through the air in waves.
00:56When something moves back and forth, it pushes and pulls the air.
01:00That movement creates sound waves.
01:03The speed of these waves is called frequency.
01:06If this frequency is low, we hear a deep sound, like a bass drum.
01:10When the frequency is high, it produces a sharp sound, like a whistle.
01:14Wee-hee!
01:14Now, at the same time, it's hard to control where sound goes, because of something called diffraction.
01:22This just means that sound waves like to spread out as they move.
01:26This is even worse with low-deep sounds, which have long waves and are harder to keep in one place.
01:32Some devices, like parametric speakers, can send sound in one direction, like a beam.
01:37Even then, the sound is still heard along the whole path.
01:41It doesn't stay in one spot.
01:43But now, researchers have actually figured out how to do that using something called ultrasound
01:49and a special trick called non-linear acoustics.
01:54Now, ultrasound is a sound that's too high-pitched for people to hear.
01:58Anything above 20,000 hertz or 20 kilohertz.
02:02Even though we can't hear it, it still travels through the air like a regular sound.
02:06It's used in things like medical scans.
02:08For example, ultrasound imaging, and in some industrial tools.
02:13So, in their research, scientists use ultrasound to carry normal sound.
02:17They made ultrasound waves move through the air quietly,
02:21and the actual sound only became audible right where they wanted it to.
02:26Now, usually, sound waves just add up when they meet.
02:29That's called linear behavior.
02:31Nothing special happens, the sounds just mix together.
02:33But when sound waves are strong enough, they can act differently.
02:37They combine in a non-linear way, which can create new sounds that weren't there before.
02:43Using this knowledge, the researchers took two ultrasound beams, each at a different high frequency.
02:50By themselves, these beams were totally silent.
02:52But when they met in space, they mixed in this non-linear way and created a brand-new sound wave that we could hear.
03:01And that sound only appears in the spot where the beams cross.
03:05Normally, sound travels in straight lines, unless it bounces off of something.
03:10But researchers used special materials called acoustic metasurfaces.
03:15It allowed them to bend those ultrasound beams as they moved.
03:19Kind of like how glasses bend light.
03:22By changing the timing of the waves really precisely,
03:26they can curve the sound around objects and make it reach an exact point.
03:30Like sending it around a corner and having it land right by your ear.
03:34Now, let's say they use one beam at 40 kHz and the other at 39.5 kHz.
03:41When these beams meet, they create a sound at the difference between those two.
03:460.5 kHz or 500 Hz, which is a frequency we can hear.
03:51But again, you only hear it right where those beams intersect.
03:56Everywhere else, silence.
03:58Even so, you could send sounds straight to one person without headphones
04:02and not disturb anyone around them.
04:06Imagine walking through a museum and hearing an audio guide just for you.
04:10No headphones needed.
04:12Other people nearby could be listening to totally different information
04:15without any sound overlapping.
04:18In a library, students could listen to lessons
04:20without bothering the person next to them.
04:23In a car, this tech could let passengers listen to music
04:26while the driver hears only the GPS directions.
04:29Aw, man!
04:30In offices, it could create small zones
04:33where people could have private conversations without being overheard.
04:37It could also work the other way around,
04:40by canceling noise in a certain spot to make things quieter.
04:43This could help people concentrate better at work
04:46or even reduce noise in busy cities.
04:49Now, this isn't something you'll be able to buy just yet.
04:52There are still some challenges.
04:54For one thing, the sound quality can get a bit distorted
04:57because of how the ultrasound waves interact.
05:00Also, turning ultrasound into sound you can hear takes a lot of energy,
05:05which makes it less efficient right now.
05:08Still, the idea of creating audio bubbles is absolutely fantastic.
05:12It's not the only recent invention that explores sound.
05:17How about AI headphones that allow you to focus on just one voice?
05:21You might say that these days,
05:23we already have noise-canceling headphones that can block out sound,
05:27but you really don't get to choose what to focus on or when.
05:31But researchers from the University of Washington
05:34have come up with a smart solution.
05:36They've built a system called Target Speech Hearing
05:40that works with AI and headphones.
05:43You just look at the person you want to hear for about 3 to 5 seconds,
05:46and the headphones will lock on to their voice.
05:50After that, the headphones block out all the other sounds around you
05:54and play only that person's voice in real time.
05:57And even if you're in a loud place
05:59or you walk around and aren't facing them anymore,
06:02it still works.
06:03The headphones aren't for sale yet.
06:06But the code is out there, and others can't experiment with it.
06:09Let's dive deeper into how it all works.
06:12You wear regular headphones that have built-in microphones.
06:15When you want to hear someone,
06:17you just press a button and look at them while they're speaking.
06:20The system figures out who you want to hear
06:23by measuring when their voice hits both microphones at the same time.
06:27There's a small margin of error, but it works pretty well.
06:31That sound is then sent to a small computer built into the headset.
06:34The AI software listens and learns the voice you've chosen.
06:39From that point on, the system keeps picking out that person's voice and playing it clearly to you,
06:45even if you're both moving around.
06:47The more that person talks, the better the system gets at recognizing and focusing on them.
06:52They tested this on 21 people, and on average,
06:56the sound of the selected voice was rated nearly twice as clear as the normal unfiltered sound.
07:02Now, right now, the system can only focus on one speaker at a time,
07:07and it has trouble if another loud voice is coming from the same direction.
07:11But if the sound isn't clear enough,
07:14you can just do another enrollment to help it improve.
07:17They're now working on making the text small enough to fit into earbuds and hearing aids.
07:23Scientists have also found that the human ear itself has hidden modes.
07:27Researchers at Yale University were just trying to figure out how our ears can pick up super quiet sounds.
07:34And in the process, they discovered a hidden way that the ear might handle low-frequency sounds.
07:40You know, those deep rumbling ones?
07:42It helps us hear better without getting overwhelmed by noise.
07:46Scientists think that the cochlea, which is the spiral-shaped part of the inner ear,
07:51might be using a whole set of low-frequency mechanical modes.
07:55Basically, when sound comes into your ear,
07:58it creates tiny vibrations that travel through the cochlea.
08:02Inside, little hairs on a membrane detect those vibrations
08:05and send signals to your brain so you can hear.
08:08The problem is that these vibrations can weaken as they travel,
08:13making sounds dull or quiet.
08:15Now, we already knew that certain parts of these hair cells
08:18can boost those signals with a well-timed kick to make the sounds clearer,
08:23kind of like a built-in amplifier.
08:25But now, it looks like the ear has another trick up its sleeve.
08:29It can also tune and boost sound more broadly,
08:33especially for low-frequency sounds.
08:34And it does this without making up fake sounds or overreacting.
08:40New models show that the hair cells can work not just individually,
08:44but also in larger groups all at once.
08:46This lets the ear adapt and control how it processes vibrations.
08:51For lower-pitched sounds,
08:53even big sections of the membrane in the cochlea
08:55can work together to keep the sound clear
08:58and avoid overwhelm in the system.
09:00This discovery might explain
09:02how we're able to hear such quiet low sounds in the first place.
09:06That's it for today.
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