What is the technology behind ANC?

Increasingly ubiquitous in the audio industry, active noise cancellation (ANC) (also known as active noise reduction (ANR)) technology is no longer a luxury reserved for just the most expensive headphones. In fact, ANC headphones are more popular than ever because technological innovation has enabled the integration of ANC into more platforms at lower price points.

Despite the submission of a patent application describing the principles of ANC technologies all the way back in the 1930s, I’m sure Dr. Lueg never envisioned noise-cancelling technology would advance to the point it’s reached today. Even as few as five years ago, it wasn’t possible to stick truly wireless earbuds with active noise cancellation into your ears. But now, countless articles are published detailing the “best noise-cancelling true wireless earbuds of 2020.”

Evolution of ANC Technology

Initially, analog circuitry was included in the electronics of a device because digital technologies weren’t yet far enough along, active noise cancellation/reduction requires a very fast response to external noise in order to be useful. Unfortunately, these early analog circuits were not all that accurate at reducing the noises.

We could achieve a certain amount of noise reduction with analog circuits and filters, using transistors, but it wouldn’t work well when trying to listen to music in an unobtrusive manner. And let’s be honest, that’s the primary consumer application for noise cancellation.

Fortunately, advances in digital technology have revolutionized active noise cancellation, enabling further miniaturization to the point where we’re now seeing noise-cancelling earbuds because we’re able to move ANC processing into either a digital signal processor (DSP) engine on a Bluetooth chip or into very small DSP chips running custom algorithms.

How Does Active Noise Cancellation Technology Work?

Active Vs. Passive Noise Cancellation

First, let’s put aside the active aspect of noise cancellation. Passive noise cancellation is not so much cancellation as it is noise reduction. When discussing passive noise cancellation, consider someone wearing a bulky pair of earmuffs or earbuds on a construction site or in a workshop or industrial setting. Unwanted ambient noises are blocked out based on the physical design of the earcups, earmuffs or earbuds. As such, shape and fit are crucial to protect ears from the external noise in passive applications. If there’s a leak point, you’re less likely to get effective noise protection.

Active noise reduction, on the other hand, uses electronics to aid in preventing undesirable or excessive volume from reaching someone’s eardrums. Because sound travels in waves through the air and into your ear canal, vibrating your eardrum, if a sound wave meets another sound wave with the exact same frequency but the opposite amplitude, the two largely cancel each other out (see image below).

ANC uses tiny microphones listening to the ambient noise around you, and then the electronics in the device create a sound that is the exact opposite of that sound wave, cancelling it out so that all you should hear is the music coming from your headphones — not any external sounds. ANC headphones are more expensive than many of the passive noise reduction headphones on the market because they involve more sophisticated engineering design to produce, as well as batteries to power the active noise cancellation.

There is also impulse noise reduction, which reduces amplification for sudden, brief noises by using (usually) a single microphone to make the electronics in the device aware there is a loud external sound. Impulse noise reduction adjusts sudden loud noises, dropping outside sounds so you can experience them at a more comfortable level or carry on a conversation while protecting your hearing in a passive mode. Essentially, impulse noise reduction requires a circuit in the device that detects when a sound is skewing toward hitting the threshold, then turns that sound off.

Now that you’re thinking about active noise cancellation as using electronics to prevent unwanted sounds from reaching your eardrums, it’s important to understand there are multiple types of ANC.

3 Basic Types of Active Noise Cancellation

Feedforward ANC

Likely the simplest type of active noise cancellation, feedforward ANC puts a microphone on the outside of the earpiece to detect ambient noise. This type of ANC is typically used for two functions:

1. To hear what’s going on outside of the headphones, which is also known as “sidetone.”
2. To hear your own voice during a phone conversation. When you can’t hear yourself when talking to somebody, it can be confusing.

Feedforward ANC uses a DSP or other ANC processing hardware to map the noise signal to the frequency response you will actually hear on the inside of your headphones. Whether it’s an impulse noise or continuous external loud sounds, the feedforward microphone picks up the noise before your ear does and adjusts the signal given to your ears by the internal speaker, cancelling out the noise being sent to your ear. Basically the same as impulse noise reduction, but feedforward ANC is better for more complex sounds because it’s a more complex algorithm. However, feedforward ANC is not as accurate as placing a mic inside the ear.

Feedback ANC

That’s where feedback ANC comes in. The opposite of feedforward, feedback ANC places the microphone inside your earpiece. The feedback microphone detects noise that has made it into your ear/ear canal, working with electronics to remove the noise from the signal while also adding a signal that cancels the noise that’s getting into your ear.

With feedback ANC, we’re taking passive noise reduction, impulse noise reduction and feedforward active noise cancellation a step further. The feedback microphone detects the actual noise that’s in the ear, leveraging even more effective algorithms to provide additional decibels (dB) of noise reduction by putting an extra signal in the ear that cancels out the noise that’s actually getting into the ear. The big bonus is that noise captured by the feedback microphone more accurately reflects noise you hear, regardless of the exact positioning and fit of the headphones.

Hybrid ANC

The best of both worlds, hybrid ANC combines both feedforward and feedback microphones and processing to achieve maximum effectiveness by augmenting whatever passive noise reduction your ear protection device is giving you.

At the end of the day, it’s important to understand the three main types of ANC because that knowledge helps inform the best option for your application. Challenges with feedback or not enough high-frequency cancellation could mean you would be better suited to go with feedforward. Alternatively, if the noise cancellation leaves a bit to be desired, you might want to switch from feedforward to feedback or hybrid. When done right, hybrid ANC should ensure a nice quiet listening environment without any issues.

At Cardinal Peak, we’re well versed in all three types of ANC and possess the expertise to successfully deliver consumer audio products that use all three ANC types and leverage signal processing to achieve the highest level of performance. Stay tuned for additional blog posts that discuss ANC at the mic and intellectual property (IP) options for implementing ANC.

In our recent What is ANC Technology & How Does it Work? blog post, we delved into how ANC technology works and the three basic types of active noise cancellation (ANC). This post will highlight another kind of active noise cancellation (although it doesn’t usually go by that name) that works to prevent undesirable sounds from getting into a voice signal — microphone noise canceling.

As a leader in audio product design and DSP engineering, Cardinal Peak employs an experienced team of engineers that excels at adding high-quality voice control to any product, as well as developing products that require ANC, whether at the microphone or in headphone applications.

Understanding the Basics of Active Noise Cancellation Microphone Technology

Imagine you’re on a conference call (who among us isn’t well versed in Zoom or another video conferencing solution by now?), and there’s a loud noise in the background of your work environment — say a dog barking or a washing machine buzzing. Wouldn’t it be wonderful if:

• The audio device you’re using to listen through would prevent that loud noise from reaching your eardrums?
• The system that’s picking up your microphone would block that noise from being transmitted to listeners on the other end?

Active Noise-Canceling (ANC) Microphones: An Overview

Enter ANC at the mic, or multi-microphone noise cancellation.

Let’s face it, we’ve all experienced making a phone call from a noisy street, busy restaurant or crowded public space in which the symphony of background noises can make it impossible to hear an incoming call. Worse yet, none of us wants to be the person in this situation who is yelling into their phone to be heard.

ANC microphone technology reduces unwanted noise in a particular environment — primarily in headphones and earbuds. This technology uses a microphone to capture the environmental noise and then generates an opposite sound wave to cancel it. While active noise-canceling microphones can minimize background noise, they also need to be able to reject noise from microphone arrays so users sound good to whomever they are talking to (whether on the phone or talking to a voice assistant).

ANC microphone technology typically includes two microphones: one that captures the environmental noise and the other that generates the sound waves that cancel it out. Unfortunately, capturing background sounds accurately enough to provide the maximum noise reduction is challenging for dual-microphone setups. From frequency responses that aren’t perfect to cancellation waveforms not lining up with the phase of the noise once it reaches your ear in an ideal manner, as well as electronic conversion introducing its own noise, it’s unlikely we’ll see 100% microphone noise reduction with current technologies — but we can significantly cut the background volume.

Feedforward vs. Feedback Microphones

Whether using a feedforward or feedback microphone for noise reduction, ANC at the mic requires a digital signal processor (DSP) or other ANC processing hardware to deal with noise filtering and map noise signals to what users will actually hear. While external feedforward microphones have the best noise sensitivity, they are susceptible to short-burst high-frequency background noises, which could be amplified. Feedback microphones, on the other hand, capture sound that more accurately reflects noise the wearer hears because the mic is located inside the ear device. The best — and most expensive — option, hybrid ANC, combines the best of both worlds (external feedforward mics and internal feedback mics) to deliver optimal noise cancellation.

Multi-Microphone Noise-Cancellation Technology in Action — Best Uses

A highly effective method of reducing environmental noise in headphones and earbuds, ANC microphone technology is transforming the consumer audio industry by providing a more enjoyable and immersive listener experience.

Beyond headphones and earbuds, ANC tech is also used in the following use cases:

• Video and voice conferencing systems to provide clearer communication.
• Smart speakers to enhance voice recognition.
• Hearing aids to provide more precise sound for individuals with hearing loss.

How Active Noise-Cancellation Technology Works with Voice Signals

While ANC has been used in headphones for people listening to music for years, advanced ANC technology only recently came to microphones for voice applications. Today, most modern mobile phones leverage a multimicrophone ANC design to cancel out ambient noise from voice signals. Sound is captured from the microphone furthest from a speaker’s mouth — the noise signal — and from one closest to the mouth — the desired voice signal. From there, each signal is processed to cancel the unwanted noise from the desired signal, producing improved voice sound quality.

The same is true of noise-canceling microphones. To achieve directionality, such microphones have at least two ports through which sound enters:

1. A front port, which is usually oriented toward the desired sound.
2. Another port that’s more distant.

Noise cancellation at the microphone doesn’t help you but allows others to hear you better, picking up your voice while ignoring any background noise.

How Microphone Noise Reduction Works to Improve Audio Quality

But how do noise-canceling microphones (and microphone noise-canceling software) know what noises are unwanted versus those that need to come through loud and clear?

While microphone shape and positioning can help with noise reduction, the simplest solution from a technical perspective is to have some frequency domain power analysis so that the ANC microphone technology can determine the difference between the desired sound and the signal that ought to be canceled.

The DSP looks at the amount of energy in frequency bands, and when a frequency band or a specific frequency — depending on the DSP algorithm’s accuracy — reaches an excessive level, the DSP puts a cancellation waveform in to cancel out external ambient noises. ANC at the microphone is about detecting the signal that doesn’t belong and canceling that undesired signal.

Essentially, one microphone is located close to your mouth to pick up your voice while another further away microphone picks up noises from your surroundings. DSP algorithms then work to remove any external noise, leaving your voice — and your voice only. In a noisy environment, both microphones receive noises at similar levels, but the mic closest to someone’s mouth receives the desired voice signal more strongly. Thus, if the external ambient noise signal is subtracted from the voice signal, much of the undesirable noise is canceled while the sound the listener wants to hear is retained.

As hybrid work advances, it’s important to remember that despite these incredible technological advances, noise-canceling headsets will not completely eliminate undesired sounds. Whether your workspace has a barking dog, crying baby, loud coworkers or noisy appliances, even the best noise-cancellation technologies only reduce external sounds by up to 75%. By reducing background noise, communication between callers improves due to less repeated and more accurate information, ultimately improving productivity.

The Benefits of Using an ANC Microphone for Clearer Audio

Noise-cancellation microphones significantly improve audio quality by reducing unwanted background noise, allowing listeners to hear more clearly and without any distractions. Additional benefits of using ANC microphone technology include:

• Better communication
• Reduced listening fatigue
• Enhanced privacy
• Increased accuracy
• Greater convenience

Today, implementing a background noise-canceling microphone and ANC circuit into a phone or in a headset is the most effective method for providing users with the high-quality voice signal they expect under almost any ambient conditions.

Cardinal Peak’s deep expertise with ANC at the microphone allowed us to recently complete a project that required audio filtering in a noisy environment. If you’re curious about voice assistants and the neural network software and new hardware that allows the use of voice technologies in low-power applications, check out this blog post. For more information on how we can support your next ANC technology project from initial architecture through product release, reach out to us today!

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