(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)
