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
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:
- To hear what’s going on outside of the headphones, which is also known as “sidetone.”
- 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.
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.
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.