What is ANC? Active noise cancellation explained

Active noise cancellation (ANC) is a feature that blocks out unwanted background noises like the humming of an aircraft engine. Over the years, it has become a staple feature on premium wireless audio products. And now, it’s often a key differentiating feature for many brands. Apple’s entry-level AirPods, for example, don’t feature ANC but it’s present on the more expensive AirPods Pro.

So in this article, let’s break down what active noise cancellation does, how it works, and when you might want to use it.

How does active noise cancellation (ANC) work?

As its name suggests, active noise cancellation is a software technique that reduces or eliminates unwanted background sounds. It also relies on the presence of either a dedicated SoC or a digital signal processor (DSP).

Audio products with ANC use an array of outside-facing and in-ear mics to record ambient sounds. The onboard processing chip then inverts these sounds in real-time and feeds the output to your ears. The outside noise and ANC output cancel out each other, thus giving you the perception of silence.

Take a look at the figure below for a more visual demonstration of ANC. Here, the sound waves are exactly 180 degrees out of phase (or the opposite of each other). If the original and inverted waves also have the same amplitude (volume), they simply combine to cancel each other out. The technical term for this is destructive interference or phase cancellation.

It’s worth noting that active noise cancellation is never perfect in the real world. Most implementations only work effectively against low-frequency sounds like engine rumbles and air conditioner hums. Higher-pitched sounds like human conversation and honking usually don’t get canceled out. The latter is much more unpredictable and, therefore, difficult to cancel. Even with a good ANC system, you can hear these sounds when the phase of the inverted output doesn’t match the background noise perfectly. You can still expect some noise reduction, but not total silence.

Our picks: The best noise-cancelling true wireless earbuds

Active vs passive noise cancellation: What’s the difference?

Passive noise cancellation refers to the natural sound reduction that you get with a physical seal from the outside world. Over-the-ear headphones achieve this seal through thick padding, while earbuds most commonly use silicone tips instead. In other words, passive noise cancellation doesn’t need sophisticated processing or hardware — it’s only a measure of how well a particular audio product can isolate your ears from the outside world.

Active noise cancellation, on the other hand, requires a chip that’s capable of recording external audio, mirroring it, and finally playing it back with as little delay as possible — all while also playing back music from a connected device.

Audio products with ANC generally also rely on a physical seal to reduce background noise, so the two work in tandem. In fact, someone using ANC with a loose seal will find that the feature doesn’t perform very well.

ANC types: Feedforward, feedback, and hybrid

The basic idea of active noise cancellation has been around for decades and we’ve seen plenty of advancements over the years. That said, ANC products can be classified as one of three types: feedforward, feedback, or hybrid.

What is Feedforward ANC?

Feedforward is the most common type of active noise cancellation, especially on earbuds where physical space is limited. This is because feedforward ANC only uses microphones on the outside to capture ambient noise.

Feedforward ANC works effectively enough to isolate sounds like road noise and traffic, but it lacks precision. It can sometimes pick up wind noise and amplify it since there are no interior microphones to correct it.

What is Feedback ANC?

Feedback ANC uses microphones situated either inside the earcup on headphones or inside the wearer’s ear. Either way, the goal is to pick up ambient sounds that the listener can hear. This gives the chip a better starting point since it’s fed a more accurate representation of background noise. It also doesn’t suffer from wind noise, since the physical seal will keep such sounds from reaching the microphone in the first place.

Audio products that rely on feedback ANC also have to ensure that they don’t end up picking up music or other audio that is meant to be heard by the listener. To achieve this, the onboard chip has to perform additional processing to retain only the external noise.

What is Hybrid ANC?

As you may have guessed, hybrid ANC combines feedforward and feedback techniques to get the best of both worlds. In other words, you have microphones on both the outside and inside to get a better understanding of which background sounds make it through.

Since there’s a lot more hardware and processing involved, you’ll mostly find hybrid ANC on high-end audio products like the AirPods Pro and Bose QuietComfort 45.

Is active noise canceling worth it?

ANC allows you to enjoy your music without background noise or other distractions, but is it necessary? Not always, especially if you intend to use it in environments where noises are high-pitched or sudden. Active noise cancellation also doesn’t do much for voices so it won’t offer much improvement over passive isolation in a busy office. Higher-end headphones like the Sony WH-1000XM5 do a better job here, but even then, don’t expect complete silence.

On the other hand, if you’re a daily commuter or fly often, ANC could make a meaningful difference in your life. This is especially true if you find yourself turning up the volume to compensate for background noises. In that case, noise-canceling headphones or earbuds could also help prevent hearing damage.

Headphone buying guide: A beginner’s guide to all things headphones

FAQs