What is ANC and how do noise-cancelling headphones work?

Noise-canceling headphones and earbuds are a boon. If you’ve ever owned a pair, you’ll know their ability to create a peaceful, noise-free listening experience that’s excellent for listening to music, blocking out traffic noise, and even working. And if you’re thinking of investing in a set, now’s a great opportunity for you. Of course, not all noise-cancelling products are created equal, but many of these devices are unified by some common audio technology. One feature that many of these headphones and earbuds use is called active noise-cancellation, or ANC.

When it comes to noise cancellation, you can think of ANC as the base. But how does all this impressive circuitry and sound processing actually work? What does jargon mean? Who are the big players? We’re here today to give you a crash course in ANC and its many audio offshoots.

What is active noise cancellation?

Man wearing Sony WH-1000XM4 ANC headphones on public transport.

If you ever took an introduction to physics class in high school or college, you’ll remember the section that covered waves. Waves made of water, or light, or sound all have certain intrinsic properties. ANC technology takes advantage of one of these properties: any wave can be effectively “canceled” if you create a second wave that is exactly the opposite of the first wave – a process known as destructive interference. Is.

So if you can create a set of headphones that can listen to the outside world and immediately create a set of sound waves that are exactly the opposite of what is being heard (called anti-noise), then, In theory, you would. Don’t listen to outside sounds at all – they will have been canceled out before they reach your eardrum. This is exactly what the ANC does.

Bose, the company that developed the first commercial ANC headphones for pilots and then the first ANC headphones for the general public, describes it this way:

With microphones inside and outside the earcups, Bose noise-canceling headphones continuously sense unwanted sounds, measure and send them to proprietary digital signal processing chips that respond to changing noise in less than a fraction of a second. Calculates exact, equal and opposite signals. millisecond. The result is that the surrounding noise almost disappears.

However, not all ANC is created equal, which means that even though all ANC headphones and earbuds use the same principle, there can be big differences between brands and models.

Active vs Passive Noise Cancellation

Man wearing Bowers & Wilkins Px8.
Simon Cohen/

As great as ANC can be, it’s worth noting that it’s not the only way to deal with noise. Passive noise cancellation (sometimes called passive noise isolation) takes a decidedly low-tech approach to the problem by creating a physical barrier between your eardrums and outside sounds.

This is usually accomplished by creating a tight seal around your ears (if it’s a set of headphones) or inside your ear canal if you’re using earbuds. Either way, the result is the same: You won’t hear sound that couldn’t reach your ears in the first place. When passive noise cancellation is done well, it can be so effective that you don’t feel the need for anything else.

It’s also worth noting that despite using different methods, active and passive noise cancellation actually complement each other. The more sound you can passively block, the better the ANC technology can cancel out the sounds that still come through.

Think of it like paint: If you use a layer of primer on your walls, you’ll probably need fewer layers of paint to get the color and coverage you want than if you applied the paint straight on.

What is the difference between ANC and ANR?

You may have seen the term active noise reduction, or ANR, in addition to the more common ANC. In practice, there is no difference between them. Each company uses its own preferred label, but it has the same features.

Interestingly, Bose uses both terms, but in different circumstances. When Bose makes its own noise-cancelling headphones, it calls them ANC, because Bose is 100% responsible for the performance of those headphones. But sometimes third-party companies will license Bose’s noise-canceling technology to make their own ANC headphones. Amazon did this when it introduced its first generation Echo Buds. When this happens, they use the term ANR to refer to third party Bose contributions, as a way of indicating that Bose was not involved in every aspect of the headphones’ performance.

How do ANC headphones and earbuds work?

Man listening to Apple AirPods Max.

All ANC headphones and earbuds use microphones to detect external sounds. An onboard microprocessor analyzes those sounds and feeds the necessary contrasting sound waves into your ears through the headphones’ speakers. Amazingly, this can be done whether you’re playing music or not.

Some ANC models use “feedforward” microphones. These mics are placed on the outside of the headphones, where they are able to capture external sounds clearly and quickly. But feedforward ANC systems don’t know what happens to external sounds when they pass through the noise-isolating barrier of the earcups (or ear tips). This means that the anti-noise they produce may not exactly match the noise entering your ears.

Other ANC systems use “feedback” microphones, which sit inside the earcups of the headphones. They get the most accurate readings on external sounds entering the headphones, so they should be able to create the most accurate noise canceling. But these systems are not as efficient at canceling high-frequency sounds as feedforward mics. They also have to contend with any music you’re listening to. It can be difficult to be able to distinguish between the sound you want to hear (your music) and the sound you want to cancel, and the feedback system runs the risk of canceling out some of your music.

As you might expect, the best ANC systems use a hybrid of feedforward and feedback models and use both internal and external microphones to deal with noise. If you see a set of headphones that has “Hybrid ANC” listed on it, it uses this method.

Adaptive ANC

A relatively new term in the headphone sphere, Adaptive ANC can mean different things depending on the model of the headphones and the technology being used.

Qualcomm’s Adaptive ANC technology, for example, helps the ANC circuitry respond in real-time to changes in the volume of external sound that makes its way inside the headphones’ sealed area. This is an attempt to compensate for the fact that there are hundreds of different ear and head sizes, making it difficult for any one model to fit all people perfectly.

Girl wearing Nuraloop ANC headphones.
Qualcomm’s active noise cancellation is featured in the Neuraloop headphones. nooraloop

Even if you get a great seal with a set of earbuds, as you walk, run or even talk, the earbuds will naturally move around inside your ears, altering that seal. Qualcomm’s Adaptive ANC reacts to these changes.

The second form of Adaptive ANC relates to the algorithms used by the ANC circuitry. External sounds constantly change depending on our environment. Indoors, we’re likely to find a lot of people speaking, while outdoors we may encounter traffic sounds, and on airplanes, it’s mostly the white noise of jet engines. Many companies offer smartphone apps that let you select the appropriate ANC mode based on your surroundings, but Adaptive ANC systems attempt to analyze those changing sounds and shift modes automatically so you always have an optimized noise -Experienced cancellation.

What makes one set of ANC headphones better than another?

This is a million dollar question. Honest answers are everything. ANC is much more than external and internal microphones combined with some circuitry. This is the number, location and type of microphones used. This is the quality of the electronics used to connect the components together. This is the sophistication of the noise-canceling algorithms, and this is the sensitivity of the drivers used to generate both sound and anti-noise.

Because ANC is so complex, buyers need to be wary of manufacturer claims such as noise volume expressed in decibels (dB). You may see a set of ANC headphones that claim to cancel -35dB of noise. But what does this mean? Unwanted sound is not just measured by loudness – it is also composed of a spectrum of frequencies. If the ANC system reduces high-frequency sounds by -35dB, but barely reduces low-frequency sounds, is that good or bad? If you’re trying to block out the sound of the neighbor’s kids (or maybe your kids) screaming while they play, this can be very helpful. But since most of us won’t want to wear separate headphones to block out ambient noise, this probably isn’t the right choice.

Our advice, which won’t surprise you, is to read both professional and buyer-based reviews to find out how your chosen model handles different situations.

What can I expect from a good set of ANC headphones?

Man wearing Sony WH-1000XM4 ANC headphones on public transport

Any ANC headphone or earbud worth having should provide an immediate and very noticeable reduction in external noise. Most ANC headphones also have a transparency mode, which is designed to let a lot of noise in (so you can maintain awareness of hazards or have a conversation without removing the cans). In an ideal world, Transparency mode would make you feel as if you’re not wearing headphones at all.

When you turn off Transparency and ANC, things should become much quieter, but you’ll still be quite aware of outside sounds. Turning on ANC should reduce the remaining sounds significantly. In some cases, ANC can make sounds (like the hum of a fan) disappear completely, giving you a feeling of almost complete silence.

What are some symptoms of bad ANC headphones?

The first and most obvious sign is that turning on the ANC function does not reduce the sounds you were hearing before turning it on. This may seem obvious, but we’ve tried a few models where it was almost impossible to tell when ANC was engaged.

Another problem is that ANC can start to affect the quality of your music. Remember, the same speakers that produce your tunes are also producing the anti-noise that cancels out unwanted sounds. If the ANC system is too aggressive, poorly tuned, or suffers from a number of other weaknesses, you may find that music sounds significantly worse when ANC is on.

Finally, poorly designed ANC circuitry may actually introduce new noise, even as it tries to cancel out unwanted noise. This often appears as a whispering sound that you can hear when you are not listening to any content. Playing music may mask this whisper, but if you want to use your headphones as an alternative to earplugs, that audible whisper is guaranteed to drive you crazy.

What about Environmental Noise Cancellation (ENC)?

When reading product descriptions, pay special attention to terms like environmental noise cancellation (ENC), clear voice calling (CVC), or noise-cancellation (without “active”). These are all references to the noise-cancellation performed by the microphone circuitry to reduce the impact of background sounds when you’re talking to someone on a call or using headphones to record your voice.

This is definitely a feature you want in a set of headphones or earbuds if you plan on using them for voice calls, but it’s not a separate form of active noise cancellation and won’t have any effect on noise volume. It won’t make any difference. You listen while listening to music or just wearing headphones.

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