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What is Active Noise Cancellation (ANC), How It Works & Types Explained

Last updated: 9 months ago
12 min read

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Active noise cancellation eliminates ambient noise by generating its opposite sound.

We go into detail below, so read the article. It explains:

  • How ANC works
  • What types of ANC exist
  • And when it’s best to use
How Noise Cancelling Headphones Fight Sound Waves guide

Key Points

KEY TAKEAWAYS

CONTENTS (show more)

    What is Active Noise Cancelling

    Active noise cancelling is a technology that creates an identical but inverted signal (anti-noise) of the outside noise in order to cancel it out. To do that, it requires a microphone to record a signal and an ANC chip to process it.

    It’s different from passive noise isolation, which solely relies on noise dampening of materials (physical barriers). For example, thicker plastic ear cups’, and denser earpad foam isolate more noise.

    Sony WH-CH710N earpads depth
    Thicker earpads not only help with passive isolation but also strengthen noise cancellation.
    • ANC is typically the most effective at removing lower frequencies (bass).
    • Whereas passive noise isolation better removes higher frequencies (treble.)

    Lower frequencies have larger wavelengths, so they’re harder to absorb, whereas high frequencies are so tiny even your skin can absorb them.

    And that’s why headphone manufacturers try to combine the best of both worlds to deliver the best noise-removing results.

    Where can you find ANC?

    You can find active noise cancelling technology primarily in Bluetooth headphones and true wireless earbuds. ANC headphones have become popular with pilots. Today, people use it to cancel out engine noise when commuting or traveling, to help them concentrate at work, and to help them fall asleep.

    You can also find it in cars. Car manufacturers started implementing ANC into premium models to reduce wind, tire, and road noises.

    How Active Noise Cancelling Works

    Active noise cancelling is a complex process that happens in a split second. Here’s the process:

    1. Microphones pick up ambient noise and send the recording to ANC circuitry (DSP).
    2. DSP uses an algorithm to correct the recording to sound more like you hear it. ANC headphones must do that because whatever microphones pick up isn’t a true representation of the surrounding noise.
    3. Also, once the outside noise reaches your ears, it loses some volume. The algorithm has to take this into account.
    4. Once the signal is “corrected”, a DSP inverts its phase.

    In practice, waveforms of the noise and signal are similar, but where one signal has a positive amplitude, the other has a negative amplitude. By combining the equal plus and minus, they cancel each other out. More about destructive interference later.

    1. The inverted signal is then sent to DAC for conversion and to an amplifier, which plays it into your ears through speakers/drivers.
    2. When the two signals meet, they cancel each other out. The more similar the inverted signal is to actual noise, the better cancellation you get.
    how active noise cancelling works
    How active noise cancelling works in the picture. source: Analogictips

    Here’s a simple analogy:

    Each sound has a frequency. And if background noise has a frequency of 5 (for simplicity’s sake), what number do you have to sum it with to get 0?

    5 + (?) = 0

    Calculating the correct number is the job of ANC. It has to be the same strength (5) but inverted, so (-5).

    5 + (-5) = 0

    It’s basic math with sound waves done in an instant.

    Where is ANC most useful? In headphones.

    Read more about noise-cancelling technology in headphones here.

    Or check the best sub-$100 ANC headphones.

    What are sound waves?

    A sound wave is a disturbance of particles over a medium (air, bone, water, etc.) that travels away from the source in a wave-like form. It’s a pressure wave.

    Image the ocean waves traveling from the source of disturbance all the way to the shore. Particles of water disturb the water next to them, and the energy is transferred over the medium.

    EarFun UBOOM L water test
    Speaker vibrations pushing water in the air.

    The source of sound disturbance can be a person’s vocal cords that disturb the air around them. Through repeat air particle disturbance, your eardrums pick up the vibration. You interpret these vibrations as the person’s voice.

    The vibration of air travels in all directions from the source and loses its power over distance. So, over distances, the voice volume is lower than at its source.

    How fast can sound travel over the air?

    Sound travels at the speed of 343 meters per second (m/s) over the air and even faster over liquids (water) and solid matter (like bone or metal). This is also how bone-conduction headphones work.

    What is destructive interference?

    Destructive interference is a phenomenon where one of two identical signals has its phase inverted, which leads to the “destruction” of both signals.

    Destructive constructive interference
    Destructive interference creates silence, whereas constructive interference amplifies the original signal.

    As described above, you achieve destructive interference by fully inverting the amplitudes of the original signal. Both signals will sound the same when played individually, but you’ll hear complete silence if you play them simultaneously.

    The amplitude in the waveform represents loudness or energy. As you add an equal amount of opposite energy, both amplitudes cancel out.

    Remember the analogy of summing a number with the same number but in a negative form (5-5=0).

    On the flip side, if you don’t invert the second signal, the two signals combine and boost in loudness by 3dB (or 50% more than before).

    ANC system components

    Active noise cancellation requires a few components to work properly. Based on the process explanation above, you can already guess which ones.

    Microphone

    A device responsible for canceling noise requires at least one microphone. The more mics it has, the more accurately it can capture external sounds and cancel them out.

    More about different microphone configurations later.

    Treblab WX8 mic holes
    You can see one microphone facing out and the other at the tip of the stem.

    ANC chip

    ANC chip is basically a dedicated DSP processor that’s built into a device. Onboard processing speeds up the process, minimizing latency and increasing effectiveness.

    However, it is best to have a dedicated ANC chip to get the best results. In the case of Jabra Elite Active 75t, the feature was added a year after the launch. However, since they don’t have a specific chip, their ANC is rather poor.

    DAC

    DSP only changes the bits (1’s and 0’s) of the signal, so a DAC (digital-to-analog converter) is needed to interpret those bits and create an analog signal.

    Amplifier

    A signal from DAC is weak, so it needs to be amplified. In this case, to the same amount as the outside noise. The boosted signal is then sent to the driver, which plays it into your ears via vibrations.

    Internal amplifier circuit
    This is an amplifier circuitry for room speakers. Of course, the amp in headphones is much smaller.

    Digital signal processing

    ANC chip is essentially a DSP, which stands for “digital signal processing” (or processor, depending on who you ask). Noise picked up by microphones must be processed before it’s played in your ears.

    So, the noise goes through a DSP, which changes the signal according to the ANC algorithm instructions.

    Types of Active Noise Cancellation

    Jump to the types of active noise cancellation below:

    Active & adaptive ANC

    Active noise cancellation works in 2 states: actively or adaptively.

    • Active noise cancellation works constantly at the same power. Normally, cheaper ANC devices use an active state to avoid extra noise processing. While that isn’t bad from a performance standpoint, it’s also the most energy-consuming.
    • Adaptive noise cancellation adapts its intensity based on the loudness of the surrounding sounds. That involves some extra processing of the ambient noise to determine the ANC intensity. Future ANC devices will take adaptive ANC even further and only reduce specific sounds while letting you hear the others, like the person you’re talking to or a nearby danger or siren.

    How ANC works also changes depending on how many and where the microphones are located.

    Jabra Elite 85H with adaptive sound mode at CES2019
    Jabra Elite 85H are one of the first headphones that came with adaptive noise cancellation.

    Feedforward active noise cancellation

    Feedforward ANC uses only external microphones to capture ambient noise.

    • Hearing outside noise sooner than you, ANC chip has more time to calculate & generate the inverted noise.
    • Since it can hear the noise better, this kind of mic configuration is better at reducing frequencies up to 2kHz.
    • However, the noise you actually hear gets reduced by passive isolation. So, without an internal mic, such ANC configuration can only guess its true loudness.
    • It cannot self-correct.
    • The feedforward mic isn’t very effective with lower frequencies and can suffer from wind noise.

    What does this mean for the user?

    • Feedforward mic hears ambient sounds before they reach your eardrums. While the distance seems negligible, it ensures the processing of the inverted signal can take “a bit longer”. That way, no sound (theoretically) can’t escape into your ears without interacting with a generated counter sound. Basically, there’s a higher chance to cancel out the noise.
    • On the flip side, since there’s no feedback (internal) mic, headphones don’t know how successful they are at blocking noise.
    • Also, they don’t know which sounds are actually getting into your ears. Therefore, they can’t self-correct their ANC performance and make it better. As a result, you get to hear a lot more of the wind noise and more lower frequencies.
    Feedforward mic ANC
    The feedforward mic is located outside the ear cup.

    Feedback active noise cancellation

    Feedback ANC uses only internal microphones to capture ambient noise.

    • ANC is more effective than with feedforward configuration, especially in lower frequencies.
    • Internal mic can correct itself & even adjust performance based on how users wear the headphones.
    • Feedback mic system can lead to quieter bass response.
    • Less ideal for reducing higher frequencies.

    What does this mean for the user?

    • Feedback (internal) microphone hears precisely what a user hears, so it knows exactly which sounds to cancel out.
    • Because of that, the ANC chip can correct its performance even if the user wears the headphones incorrectly.
    • A potential downside is that such ANC could mistake the bass from your songs for unwanted noise, reducing the bass punch and sucking out the energy from bass guitars.
    • Internal mic has difficulty capturing higher frequencies, making such ANC ineffective against mid and high-frequency noise.
    Feedback mic ANC
    The feedback mic is located inside the ear cup.

    Hybrid active noise cancellation

    As you might’ve guessed, a hybrid ANC uses both feedforward and feedback mic array, combining the positive characteristics from both.

    • Hybrid ANC is overall more effective across a wider frequency spectrum and stronger at reducing noise.
    • A bit more resistant to wind noise.
    • More expensive to implement.

    What does this mean for the user?

    • A hybrid microphone array takes the best of both worlds. It has the ability to reduce a wider range of frequencies, it’s more resilient against wind noise (although you shouldn’t expect miracles), and can self-correct itself depending on how a user wears the headphones.
    • A main downside to the hybrid configuration is the price increase needed to implement more microphones and develop more complex algorithms to make it work properly.
    Hybrid mic ANC
    Hybrid ANC uses microphones that are inside and outside an ear cup.

    Comparison of different types of ANC

    Here is a quick view of the main differences between different ANC types. While hybrid is the best, it also adds the most to the cost of the headphones.

    Feedfoward ANCFeedback ANCHybrid ANC
    Overall
    effectiveness
    GoodGreatBest
    Effectiveness
    in high frequencies
    GreatGoodBest
    Effectiveness
    in low frequencies
    GoodGreatBest
    Effectiveness
    against wind
    PoorGreatGreat
    Main issueWind noiseQuieter bass
    response
    Expensive
    to implement

    Benefits of Active Noise Cancelling

    ANC was first designed for professional use. Reducing noise in helicopter and airplane cabins to protect hearing and improve communication with pilots. Today, ANC headphones are an important feature in many people’s lives.

    Not only for commuters and travelers who are sick of listening to engine rumble. The benefits of ANC technology even extend into improving users’ health.

    Here are the ANC benefits:

    Reduces stress and ear fatigue

    We live in a noisy world where up to 40% of Americans live in dangerously loud areas.

    But what you might not know is that noise is a slow killer. It’s responsible for various physical problems (headaches, respiratory, cardiovascular, and sleeping issues) and psychological problems (stress, depression, agitation, and memory issues).

    Sleeping with headphones
    Using ANC in a noisy environment can help you fall asleep.

    Here’s how ANC reduces stress & fatigue:

    • Wear ANC headphones during work to remove background distractions. This helps you focus on the task at hand, improving productivity.
    • Do you have noisy neighbors? Put on ANC headphones to help you fall asleep and wake up rested.
    • Public places are often loud. Lower ear fatigue by minimizing noise exposure.
    • This also protects you from noise-induced hearing loss and keeps you hearing into your old age.

    Removes background noise

    If you’ve ever taken a ride on public transport (or a plane), you know how noisy it is. Engine hum damages your listening experience. Using active noise cancelling makes a night and day difference in these situations.

    Removing background noise makes you hear small details in the music again. It’s much more enjoyable.

    Improves productivity and focus

    Concentration is important. You avoid making mistakes. But with constant noise around you, your focus can shift to other things.

    And BAM, you just accidentally sent a folder of “cat memes” to a client instead of the quarterly report.

    So, using ANC reduces unwanted distractions. Many people use it in offices to help them focus on their work.

    ANC minimizes distracting sounds from your surroundings, helping you to focus on your work.

    Limitations of ANC Technology

    We have already touched on some of the limitations of active noise cancelling technology. Let’s discuss them in more detail.

    Varying effectiveness for high vs. low frequencies

    Depending on what type of ANC you’re using, you get different effectiveness against different frequency ranges.

    • Low-frequency sounds have a long wavelength and are usually pretty constant (like engine hum), which makes them the easiest to cancel out.
    • High-frequency sounds have a really short wavelength and typically vary in loudness and frequency (like human speech), so the ANC algorithm struggles to create the right cancelling noise.

    Shortens battery life

    If you’re a bit of a computer person, you know that processor is one of the more power-hungry components. Well, active noise canceling technology uses a lot of processing to analyze and create the opposite signal.

    In practice, enabling noise cancellation draws at least a third more energy than with ANC turned off.

    For example, 6 hours per charge without ANC is 4 hours with ANC.

    Quite a difference.

    But it was even worse in the past when ANC used up over half more energy. So, we expect the battery efficiency to get better in the future.

    Treblab WX8 wireless charging
    Using ANC with noticeably shorten your battery life by at least a third.

    Not effective for all noise

    Noise cancellation works best on consistent sounds rather than constantly changing ones. Sudden noises are difficult to eliminate with today’s technology. Processing power and algorithms simply aren’t good enough (yet).

    One thing that we haven’t discussed yet is the processing latency. To get the best cancellation results, the counter noise needs to be generated in real time, which is impossible.

    Primarily because the recorded signal needs to go through all the processing mentioned above. This means that there is always a little bit of latency. Which is why sudden noises can still pass through even on class-leading ANC devices (like the world-leading Sony WH-1000XM5).

    How Effective is Active Noise Cancelling at Removing Noise

    Generally, most ANC headphones remove between 20-30dB of ambient noise. Only the category-leading models can remove more than 30dB.

    Manufacturers typically make bold claims about how much noise their noise-canceling headphones reduce.

    We frequently see claims of more than 40dB reductions which never materialize during our ANC tests.

    Apple AirPods Max on the streets
    Even high-end over-ear headphones like Apple AirPods Max can’t consistently reduce all frequencies by more than 40dB.

    Most of the manufacturer decibel reduction claims are either cherry-picked or entirely misleading.

    ANC measurements

    When looking at the ANC measurement graphs, you have to focus on frequencies below 1kHz since most frequencies above that get reduced by passive noise isolation.

    Often you see the highest noise reduction at the highest frequencies, so the marketing team might use those results to promote ANC effectiveness. Even if the actual cancellation in lower frequencies doesn’t get close to the advertised decibels.

    Cherry-picked results

    Just like when manufacturers state a total harmonic distortion of their product, measuring it only at 1kHz (even though THD could be much worse at other frequencies), ANC results are also cherry-picked.

    For example, the best ANC headphones we’ve tested are Apple AirPods Max. As seen from the graph, they’re the most effective at 200Hz, reducing it by precisely 41.3dB.

    Apple AirPods Max - ANC vs passive isolation

    This means Apple can easily advertise that their headphones reduce noise by more than 41dB. Even if AirPods Max aren’t as effective at other frequencies other than 200Hz.

    Don’t get us wrong, AirPods Max are excellent, we’re just giving an example.

    Where is Active Noise Cancellation Used

    While you mostly know active noise cancellation technology from consumer headphones, it was first implemented elsewhere. And it’s extending into other fields (like the car industry).

    Use in aviation

    ANC systems in the form of headsets were first used in aviation. Developed by Bose, those headsets eliminate predominantly low-frequency noise inside a cockpit.

    That has two major benefits:

    • It protects the pilot’s hearing
    • And ensures a normal conversation over the radio

    Furthermore, prolonged exposure to such noise can cause discomfort, fatigue, and loss of concentration, which can lead to accidents.

    First noise cancelling headphones
    An example of the first ANC headsets from Bose in the 1990s.

    Use in car cabins

    Much like in aviation, Bose was also the first company to start developing ANC for cars. Their version is called “Engine Harmonic Cancellation” or EHC, and it was first used in Cadillac Escadale and Infinity M sedan in 2011.

    Bose’s idea was to only eliminate engine noise. They placed one mic near the engine, whereas other mics measured the cabin. The inverted signal was then played through car speakers.

    Over the years, other manufacturers started releasing their versions of car ANC.

    • Jaguar’s “Active Road Noise Cancellation” also measures and eliminates tire noise and noise from road vibrations.
    • Hyundai’s “Road-Noise Active Noise Control” tries to combat all surrounding noises at once, creating an almost completely silent ride.

    However, complete cockpit silence begs safety questions. Road noise can be annoying, but not hearing sirens or car horns alerting to danger can be dangerous, if not fatal.

    Use in windows

    Active noise cancellation is also implemented in window grilles to reduce the outside noise. Small sound-emitting devices are placed around the window opening to play the inverted sound.

    The best thing is that you can leave windows open and still get the cancelling effect. The airflow isn’t obstructed if you want to ventilate the room.

    ANC windows, if they ever become massively available, could become an excellent solution for people living in noisy neighborhoods.

    FAQ: Frequently Asked Questions About Active Noise Cancellation

    What does noise-cancelling actually do?

    Noise-cancelling records the ambient noise and tries to make an identical copy of it, which is later inverted. Phase-inverted copy is then played in your ears, where it “collides” with the actual noise and cancels it out.

    Is ANC bad for ears?

    ANC is actually good for the ears, as it removes loud ambient noise and protects your hearing, helps reduce noise-induced stress, and helps you focus during work.

    Do I need active noise cancellation?

    You need active noise cancellation if outside noise hurts your health, prevents you from focusing on your work, or masks your music when using headphones. If not, then you probably don’t need it.

    Does active noise cancelling remove voices?

    Active noise cancelling can slightly but not fully reduce voices. Frequencies during human speech change too frequently for current ANC technology to cancel them entirely.

    Is 25dB noise cancellation good?

    Yes, up to 25dB noise cancellation is pretty good. Most high-end ANC headphones can reduce slightly more than 30dB on average.

    Why does ANC feel weird?

    ANC can feel weird if it removes all bass frequencies, which tricks your brain into thinking that the air pressure has changed. Consequently, you start to feel pressure in your ears, which can lead to dizziness.

    Conclusion

    Active noise cancelling can be an incredibly helpful tool not just to make your commute more pleasant but to protect your hearing, improve your physical and mental health, and help you concentrate during important work.

    No wonder the technology is used in consumer products and professional applications, like airplane pilots and boat captains. In the future, you might even have it in your windows.

    But for now, check out the best ANC headphones: