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If you work in a busy office or have a noisy commute, noise canceling headphones are a delight. But have you ever thought about how active noise cancellation works? While blocking sound sounds simple, it actually involves advanced computer processing.

What is active noise cancellation?

Active noise cancellation (ANC) is a feature in mid-to-high-end headphones that engages in something called “signal processing” to block out outside sound. In fact, many of our favorite headphones They offer ANC. To keep things simple, ANC goes beyond earplugs and makes sure you don’t hear that baby crying on a cross-country flight. At least you won’t hear the crying as much as you would without the headphones.

It’s not completely transparent, so if you turn on a headset with ANC, you’ll hear it working in the form of a subtle hiss. This hiss is only the most audible part of the signal. ANC also reproduces lower frequencies, and these can damage the ears of some users .

How does active noise cancellation work?

ANC works by using a series of microphones strategically placed around a given set of headphones or earphones and a concept known as phase cancellation. The first step is to use those microphones to determine what the listener is hearing.

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Once the microphones have captured that sound, the digital signal processing (DSP) hardware and software inside the headphones go to work. This is where it gets complex.

You’ve probably heard the term “sound wave” before. This is sound: a series of vibrations. If you take a sound, duplicate it, and then slow it down a bit, this causes the waves to go out of alignment. The peak of one waveform plays at the same time as a peak in the opposite direction of the other waveform, so they effectively cancel each other out.

Waveforms in alignment

This rarely happens in nature, so it seems unnatural, but it works. Headset microphones use this same technique. Some headsets use a fairly crude implementation, while others use advanced hardware and software to intelligently adapt to their environment.

Two signals perfectly out of phase, canceling the sound

Some headphones, like earbuds, use microphones located on the outside. This is easier to do, especially on headphones, but it’s not the most effective method because it doesn’t accurately reflect what you hear.

Larger hearing aids may use microphones mounted inside the earpiece, closer to your ears. This means that the sound canceled by the headphones more accurately reflects what you are listening to, making the cancellation more effective.

Finally, other headphones use a “more is more” approach and put microphones inside and outside the earcups, allowing for complete noise cancellation.

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Passive vs. Active Noise Cancellation

You will see that some headphones claim to offer “passive” noise cancellation. This isn’t really noise cancellation in the sense we’ve seen so far, but it’s better to call it isolation.

Passive noise isolation is a simple concept, especially compared to ANC. It works the same way as covering your ears with your hands: putting something between your ears and a certain noise makes it quieter.

Another part of this comes when you start playing audio on your headphones. That sound is much closer to your ears, resulting in a higher relative volume, so it effectively drowns out background sound.

With headphones, as long as you have a good seal, this will block out a certain amount of background noise. The better the seal, the better the insulation. Usually this is more effective with over ear headphones or inside the ear. Over-ear headphones and other styles don’t create a good enough seal for real isolation.

None of this is fancy technology, but it is somewhat effective and definitely better than nothing. Just don’t confuse it with true active noise cancellation.

The disadvantages of active noise cancellation

As good as ANC is, there are some issues with it. The first is that, due to the microphones and processing, it requires power. This means that even wired headphones with ANC will need battery power.

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ANC also has a slight impact on sound quality. Due to cancellation, you don’t get music without processing. Usually this is only a concern for audiophiles and music purists, but it’s worth mentioning.

Finally, the biggest problem with active noise cancellation is that it blocks out sound. This is great in a safe environment like an office, but using noise-canceling headphones while out and about can be dangerous.

If you cross the street without looking and can’t hear a car horn due to noise cancellation, that could be very bad. That’s why more and more modern headsets come with built-in transparency modes.

What is transparency mode?

airpods pro on gray background

transparency mode It originally made its big debut in Apple’s AirPods Pro, but was quickly adopted by other headphone makers. Some were even doing this before, but the Apple name was the one that stuck.

The idea is closely related to noise cancellation, since it uses the same microphones. The difference here is that instead of inverting the signal and using it for noise cancellation, transparency mode reproduces that sound directly.

This means you can still listen to your music while listening to everything around you. If you are a runner or cyclist, this is an important feature. Thanks to firmware updates, this could come to many ANC-enabled headsets, so keep an eye out for updates from your manufacturer.

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