(sound waves vibrating)
- [Narrator] Here's a sound wave.
And here's its inverse. (sound wave beeping)
Combine them and you have silence.
(upbeat music) That's the basic idea
behind noise-canceling headphones.
But it takes a lot of technology
to make that seemingly simple science possible.
- We have 15 millionths of a second
to measure the noise, run it through a little DSP processor,
compute that inverse signal,
and pop it out through the driver.
- [Narrator] Here's how they work.
(digital signaling)
- [John] One way to visualize acoustic waves,
that I like to use, is a Slinky.
- [Narrator] John Rule has spent the last decade
developing new algorithms
for personalizing noise cancellation performance,
in Bose Headphones.
- [John] We draw them as sine waves,
as if something's going back and forth or up and down.
But what's really happening,
is that these vibrations are actually propagating
through the air.
The medium has stayed fixed,
but you can see that pulse of energy
sort of running through the length of it.
- [Narrator] Because sound is just waves,
you can cancel a sound wave
by introducing an equal and opposite wave.
- So what you've got is you've got an incoming sound wave.
And the way destructive interference works
is we say, "Hey, if I could generate
an equal and opposite signal, right?
I could generate the signal,
that's the inverse of that.
And if I sum those two things together,
I'll be left with a flat line.
I'll be left with zero pressure,
and that will be interpreted by my brain
as the noise having been canceled."
- [Narrator] Bose was the first company
to develop Noise Reduction Technology for headphones.
- Dr. Bose was coming back on an overseas flight
and got very frustrated by the fact,
that airplanes were very noisy.
We can control all sorts of other stuff,
why can't we control noise?
The first application that we looked
at was of canceling noise on airplanes.
- [Narrator] Pilots wore its earliest prototypes in 1986.
While the technology has gotten more sophisticated,
the basic science remained the same.
Active Noise Cancellation requires a few main components,
an outer microphone to track incoming noise,
an inner microphone that tracks sound waves
that make it inside your ear,
and also checks if more environmental noise than expected,
is making it through,
a digital signal processor to run some algorithms,
based on data from the mics, and the speaker,
which cancels the background noise,
while also playing the music or sound you want to hear.
- Think about how fast this has to happen.
The sound is obviously propagating
at the speed of sound, right?
Which is 343 meters per second.
If you think about that in terms
of the thickness of an earbud,
it's getting from the outside of the earbud
to the inside of the earbud in about 15 microseconds,
so that's millionths of a second.
We're doing math as fast as we can
to basically, cancel it out before it gets in.
- [Narrator] Because everyone's ears are differently shaped,
Active Noise Cancellation requires algorithms
that can be tuned, based on the user.
Bose, for instance, does this by playing a welcome chime,
(earphones chiming) and monitoring feedback
from the internal microphone
to customize noise-canceling filters, accordingly.
This requires a lot of testing,
to make sure the algorithms work on a wide range of users,
in all types of noisy environments.
But eliminating background noise is just the first step.
The next, is figuring out what noise to remove,
based on the context.
- I think it's really important to recognize
that noise is not bad.
Noise is critical to my brain, critical to my body.
My brain uses it to create richer experiences to fill
in what's missing, which is all the time.
- [Narrator] Poppy Crum was previously
the Chief Scientist at Dolby Laboratories,
where she worked for more than a decade.
She's led teams focused on Emergent Technologies
and platforms that impact sensory systems.
- When you think about Noise-Canceling Technology,
I like to sort of separate it
into three different categories.
You know, there's Passive Noise-Canceling,
or Passive Noise-Reduction, which is effectively an earplug.
The second layer would be Active Noise-Reduction.
I mean, it's dynamic to the system,
but it's dealing with what we would call,
stationary sound, sounds that are, you know, consistent,
they're continuous or they're predictable.
Examples of that might be
a generator or airplane noise. (generator roaring)
You know, not all the sounds in the airplane,
but that general rumble, those low frequency sounds
you're trying to get rid of, they're pretty predictable.
- [Narrator] For these predictable noises,
current noise-canceling algorithms
can quickly identify (waves crashing)
unwanted sound waves
and cancel them out.
Beyond that, things get harder.
- And then the next layer, (fan rumbling)
which is I think where, you know,
the future's still evolving,
is when you start being able to really cancel out things
that are what you would call non-stationary noise.
Things that might be
a dog barking. (dog barking)
And you know, those elements that happen,
where you can't predict 'em (crowd murmuring)
and you might be able to have a expectation
that they're going to happen,
but they're things that aren't continuous
and aren't constant.
- [Narrator] But sometimes, after your technology
has gone through so many steps to reduce background noise,
you want it back.
AirPods Pro have a Transparency Mode,
where they recreate the normal sound of your environment.
Other noise canceling earbuds also offer modes
to help you hear your surroundings,
like Bose's Aware Mode and Sony's Ambient Sound Mode,
that preserve enough background noise
to keep you alert to your surroundings.
- When you build a technology that's supposed to map
to a human experience,
you need to understand how the human system
perceives change or perceives that element you're building,
and then that becomes how your algorithm behaves,
so that you have a continuous experience of the world.
So you need labs where you can remove
or control every other element.
- [Narrator] Noise-cancellation could soon solve
more complex problems, like using machine learning
to seamlessly and intelligently
eliminate unwanted sounds or voices across various contexts.
Adaptive Audio, which is coming
to Apple's AirPods Pro soon,
combines noise-cancellation with the Transparency Mode,
so you can only hear the important sounds around you.
(bike bell ringing)
- [Pedestrian] So you can stay present
within your environment,
while distracting noises are automatically reduced.
(leaf blower blowing)
- It's the thing that everybody wants, right?
They wanna make certain noises go away.
So they still wanna hear some things,
they don't wanna hear other things.
And "Can you just gimme a set of headphones
that, you know, just cancels the stuff
I don't want to hear."
That's not a thing that we're offering yet,
but that's the kind of thing
that is being worked on.
(upbeat music ending)