What is ANC? Active noise cancellation explained

If you’re new to the wonderful world of headphones, a pertinent question you might find yourself asking is “What is ANC?” It’s something that crops up at just about every price point these days yet is often left unexplained.

The acronym itself stands for active noise cancellation and refers to a pair of headphones’ ability to reduce the impact of unwelcome external sound on your listening experience.

That basic definition only scratches the surface, however. The science behind active noise cancellation requires explanation, and there are various forms of ANC to get to grips with, so it pays to be in the know before splashing out on a pair of noise-cancelling headphones. Below, we discuss the key aspects of noise-cancellation technology, before drawing attention to some of our favourite ANC headphones.

What is active noise cancellation?

Active noise cancellation (ANC) is a technology that seeks to cancel out ambient noise in order to let you enjoy what you’re listening to free of external distractions and at volumes that won’t lead to hearing loss. As you’ll learn in greater detail below, it uses a combination of microphones and digital signal processing (DSP) algorithms to analyse external sound and attenuate it using anti-noise signals.

The history of active noise cancellation

The origins of active noise cancellation technology can be traced back almost a hundred years to 1933, when German physician Paul Lueg submitted a patent application for the idea that certain sound frequencies could be cancelled out by opposing sound waves. Nothing tangible came of the patent but Lueg’s theorising inspired others to pick up the mantle and American engineer Lawrence J. Fogel created his own noise-cancelling system for aeroplane cockpits in the mid-1950s.

However, it wasn’t until the late 1980s that the noise-cancelling headphones technology we’re familiar with today was forged. Bose founder, Dr Amar Bose, created a noise-cancelling headset for the aviation industry in 1989 and brought the feature to the commercial market soon after in the form of the original Bose QuietComfort headphones. Noise-cancellation technology has developed rapidly since then, to the point where some headphones costing as little as £30 incorporate it.

How does ANC work?

Before being able to fully grasp how ANC works, it’s important to understand how humans hear. Vibrations in the air create sound waves that make their way through our ear canals and to our eardrums, where tiny bones pick up the vibrations, which are subsequently transformed into electrical signals. These are carried to the brain via the auditory nerve, at which point they’re decoded into sounds we’re able to recognise and understand.

Active noise cancellation technology uses highly sensitive microphones to pick up external sound waves and digital signal processing to analyse them. The technology is then able to produce something close to the inverse of the original sound waves and these are combined with the original sound waves to cancel both out – a process known as destructive interference. There’s a little margin for error, so you’ll still hear some ambient sound, and some headphones are more effective at creating this antiphase signal than others.

Generally speaking, ANC systems are best at dealing with lower frequencies – below 1kHz – because these sound waves are longer and more predictable, whereas higher-frequency waves such as those created by a child shrieking fluctuate more frequently and produce a lot more information for an ANC system to take in and respond to. Consequently, active noise cancelling can attenuate lower frequencies much better than high ones.

Attenuation of external sound tends to fall somewhere between 15 and 30dB but will vary depending on the number of microphones used, how they’re set up, and the chipsets and algorithms used by a specific manufacturer. The level of decibel reduction is referred to as noise-cancelling depth, while noise-cancelling breadth relates to the frequency range a device can attenuate.

What microphones are used in an ANC system?

Headphones typically use either feedback or feedforward active noise cancelling microphone setups.

Feedback noise-cancelling systems have their microphones placed inside the earcups or earbuds in front of the speaker drivers. This way, the microphones pick up very similar waves to those that make their way to our ears.

Feedforward systems have microphones installed on the outer surfaces of their earbuds or earcups. This location means the mics are more sensitive to external sound but produce anti-signals that don’t take into account any changes to the soundwaves as they pass through the headphones.

The best noise-cancelling headphones tend to use a combination of both systems, with multiple mics analysing sound waves both internal and external to the headphones. For example, our favourite noise-cancelling headphones – the Sony WH-1000XM5 – have eight microphones placed across their two earcups: one feedback microphone on the inside of each earcup and various feedforward mics spread equally across the outside of the earcups.

Types of noise cancellation

While active noise cancellation is the overarching term you’ll come across most often, there are some other types of noise cancellation to be aware of: passive, adjustable and adaptive.

Passive noise cancellation is the least technical of the three and involves creating a physical barrier between any ambient noise and your ear canals. With in-ear headphones, for instance, that will often be achieved using a foam or silicone eartip to seal off your ear canal. In contrast, over-ear models block sound out using large padded earcups. Almost every pair of headphones will offer some degree of passive noise cancellation, even those that don’t use ANC technology.

Adjustable noise cancellation is simply an active noise cancellation system that allows the user to select different levels of noise cancelliation as opposed to employing one constant level of attenuation throughout. These are often delineated as “Low”, “Medium” and “High”, or other similar descriptors, and are selectable using the headphones’ physical buttons, touch controls or via an accompanying app.

Adaptive noise cancellation is the most advanced form of noise cancellation. Here, a separate software processor works to automatically adjust the level of noise cancellation based on the changing demands of your environment. Microphones pick up fluctuations in ambient sound and tweak ANC accordingly, while also taking into account other variables, including the fit of the headphones.

Transparency mode

Sometimes you want to be able to hear what’s going on around you, and this is where a transparency mode comes in handy. These modes use microphones to filter in and amplify external sound to increase your awareness of your surroundings, allowing you to hear important announcements or hold conversations without having to remove your headphones or pause your music. Customisation options are relatively limited for most transparency modes, though some allow you to control the level of sound being piped in using an adjustable slider and others can be engaged automatically when the microphones pick up your voice.

Are there any potential issues with ANC?

While effective active noise cancellation is a godsend in loud environments, engaging ANC on some headphones alters the default tuning significantly. Ideally, headphones should deliver a consistent sonic experience across their various modes, but poorly implemented noise cancellation can be a barrier to this.

The other problem that can affect noise-cancelling headphones is an audible humming or buzzing that’s present when ANC is switched on. This may be due to issues with the microphones, DSP, electronics or electrical interference but is often only audible when you’re not listening to music. Though not always the case, premium headphones tend to be less affected by this than cheaper headphones, so you’ll want to ensure the model you buy is up to scratch.

To help you make a smart buying decision, we’ve listed a few of our favourite noise-cancelling headphones below. For more exhaustive lists, head over to our roundups of the best noise-cancelling headphones and best noise-cancelling earbuds on the market.

The best ANC headphones to buy

Sony WH-1000XM5: Best over-ear noise-cancelling headphones

Price: £379 | Buy now from Amazon

The Sony WH-1000XM5 use eight microphones in combination with Sony’s Integrated Processor V1 and Sony HD Noise Cancelling Processor QN1 chips to deliver what the company says is its “biggest ever step forward in noise cancelling”.

“Auto NC Optimizer” tech analyses your environment and wearing conditions – if you have glasses on, for instance – and adjusts noise cancellation accordingly. You can also customise Sony’s Adaptive Sound Control technology to switch noise cancelling and audio settings based on your actions – Staying (not moving), Walking, Running and Transport – or location, with the option to add location-specific settings via an in-app GPS map.

Read our full Sony WH-1000XM5 review for more details

Anker Soundcore Life Q30: Best budget noise-cancelling over-ear alternative

Price: £80 | Buy now from Amazon

First-rate noise cancellation like that found on the WH-1000XM5 comes at a price; those with more limited budgets will want to check out the Soundcore Life Q30. ANC performance is very good for the money, with three modes tailored to different environmental circumstances: Transport (which focuses on low-end frequencies), Indoors (which sets its sights on voices and middle-range frequencies) and Outdoors (which effectively attenuates ambient sound, including wind-noise). Battery life is impressive, too, as are the ways in which you can customise how the Life Q30 sound.

Read our full Anker Soundcore Life Q30 review for more details

Bose QuietComfort Earbuds II: Best noise-cancelling wireless earbuds

Price: £279 | Buy now from Amazon

The original QuietComfort Earbuds attenuated external sound extremely well, but this second-gen model is even more effective at defending your eardrums from unwanted noise. The buds use Bose’s “CustomTune” technology to monitor sound escaping from your ears and tweak noise cancellation accordingly. You’ve got two default modes at your disposal: Quiet, which applies maximum attenuation, and Aware, which is the earbuds’ transparency mode, along with two modes that can be personalised to apply a specific level of active noise cancellation on a ten-point scale.

Read our full Bose QuietComfort Earbuds II review for more details

Anker Soundcore Life P3: Best budget noise-cancelling earbuds alternative

Price: £70 | Buy now from Amazon

Once again, our budget alternative comes courtesy of Anker brand Soundcore. Like the Life Q30 over-ear headphones, the excellent Life P3 wireless earbuds have three noise-cancelling levels to pick from: Transport (focusing on lower-end frequencies), Indoors (targeting middle-range frequencies) and Outdoors (blocking ambient sound, including wind-noise).

Read our Anker Soundcore Life P3 review for more details