Tech Talk: What is ANC and how does it work?

Welcome to Tech Talk, a weekly column about the things we use and how they work. We try to keep it simple here so everyone can understand how and why the gadget in your hand does what it does.

Things may become a little technical at times, as that's the nature of technology — it can be complex and intricate. Together we can break it all down and make it accessible, though!

You might not care how any of this stuff happens, and that's OK, too. Your tech gadgets are personal and should be fun. You never know though, you might just learn something ...

What exactly is ANC?

You probably know that people talk about ANC when discussing headphones, but you might not know what it stands for or what it means. ANC is Active Noise Cancellation, and it's an electronic means of suppressing outside and ambient noises that may be loud or simply bothersome, like a crowded bus, a crying baby, or an aircraft engine.

All headphones are noise canceling to some extent because they are either plugged into your ear or cover it. This blocks a good bit of the regular ambient noises in life, but sometimes you need a little more, and that's where ANC comes into play.

AMC uses sound itself to mute sound. Yes, you read that right. With dedicated microphones and fast microprocessors, you can say goodbye to that noisy jet engine when you're trying to sleep on a midnight flight.

Not all headphones or earbuds use electronic noise cancellation, and you'll notice the brands and models that do will cost a little more. The parts and engineering needed aren't crazy expensive, but they will add to the cost.

Additionally, some individuals cannot use headphones with any form of electronic noise suppression. I know because, unfortunately, I'm one of them. Just like a great phone screen causes trouble for some people, the method used to suppress noises can cause a terrible headache, and some people say they can even hear it. Thankfully, most people are unaffected, and headphones with ANC are quite popular and easy to find.

So how does ANC work?

The way ANC works is super cool and almost seems like some sort of secret dark magic. It's not, of course: it's pure science that's not even hard to do thanks to the way sound "works".

All sound is expressed as a sound wave. The simple diagram above gives you an idea of what I'm talking about, and you've likely seen something similar when discussing sound.

Wave is a good term because you'll find crests and valleys, just as you would on a series of waves in the ocean. The distance between the "top" of the crest and the "bottom" of the valley is called the amplitude, and an easy way to think about it is that it determines how loud a particular portion of the sound will be. The distance between the crests is called the frequency. A larger number indicates a higher frequency, which means that portion of the sound is in a higher pitch.

The most important part is that this is a constant. Different sounds will create different sound waves, but frequency and amplitude are always measurable. A computer can get exact readings of all this information, and it uses it to cancel annoying noises, combined with a good microphone and a noise-generation device of some sort. Yes, you really use noise to get rid of noise.

Let's go back to the diagram for a minute. The black line is what we'll call the zero point. The red line is the noise you don't want to hear. The blue line is what is created when a computer analyzes the red wave and recreates it.

That sound, which should be an exact copy of the noise you're trying to get rid of, is played at 180 degrees out of phase (think of it as being flipped on its head). The blue wave crests when the red wave dips in perfect harmony. This creates what's known as destructive interference.

When the amplitude and frequency of the red wave are matched in reverse by the blue wave, the total amplitude is zero. Think of a crest as +5, and a valley as -5. When you subtract 5 from 5, you're left with nothing. A zero amplitude, zero frequency tone is no tone at all - dead silence.

Because nothing is ever perfect, the waveforms won't be exactly 180 degrees out of phase consistently. This can cause a small, barely audible humming noise. You might have heard this from time to time if you use headphones with ANC, and it's what gives some people a fit when trying to use them.

Your headphones or earbuds with ANC have microphones that don't listen to whatever is coming through the headphones themselves. Instead, they are listening to the outside noise.

Using the waveform of only the outside noise and doing this bit of science on it makes it seem like it has gone away while leaving what you want to hear alone. Some headphone and earbud models have a way to turn ANC off and use the dedicated microphones to playback outside noise, and when you hear people talk about audio passthrough, that's what is happening.

You don't need to know any of this to enjoy noise-free listening, but it's always fun to know how something so cool and seemingly complicated really works.