How did headphones save you from external noise in the past?


Headphones that cover your ears so that you can’t hear a damn thing didn’t appear yesterday, or even the day before. On duty, many people require complete detachment from the outside world in order to perfectly hear what is happening in the headphones. For example, a DJ or musician during a performance needs to hear the soundtrack and feel the rhythm when playing and mixing, otherwise there will be no fervent dances, and all the guests will scatter from the party. The call center operator needs to clearly hear the speech of the interlocutor. Lurker in CS:GO can let the whole team down if he doesn't hear approaching enemies. Well, the dispatcher at the airport will not be able to communicate normally with the pilots if there is noise around, like in a smelter.

Previously, headphones with passive isolation solved a similar problem. For example, massive closed on-ear headphones sit securely on your head, and their dense ear cushions securely cover your ears from extraneous noise. The same Beyerdynamic DT 770 Pro are considered real classics of this kind, drummers especially appreciate their noise isolation. Another popular option for passive noise isolation are in -ear headphones, which are inserted deep into the ear like earplugs. The problem is that these headphones are not suitable for everyone. For many people, intracanal silicone tips provoke discomfort and headache. And bulky on-ear headphones are not the best choice for the street.

Types of Active Noise Cancellation and Differences from Passive Sound Isolation


Unlike passive noise cancellation, which is determined by the shape of the headphones, active noise cancellation works on a completely different principle. To achieve complete silence , noise canceling headphones most often use the anti-phase principle. Microphones built into the body register ambient sounds, and the built-in processor creates a twin wave with the same amplitude, but a mirror image of the phase of the original sound. The sound in phase sounds natural and comes from the center, the sound in antiphase, on the contrary, plays as if from the side. Superimposed on each other, these sounds, as it were, extinguish each other, the sound wave evens out, and the listener's brain is sure that there is silence around. In the top-end headphones of the Apple AirPods Pro caliber, this happens about 200 times per second. This is the most common type of noise cancellation and is called Active Noise Cancellation (or ANC, which stands for Active Noise Canceling).


At first, many audiophiles were hostile to the new idea. Say, brothers, marketers again want our money. We won't give them a penny, we'll use everything for gold-plated cables. In addition to banal distrust, criticism arose due to the lousy quality of the first headphones with digital noise cancellation. First, they sounded so-so. Secondly, instead of a hybrid microphone system, they used poorly tuned noise cancellation without feedback. They were notable for their inconsistency and often introduced artifacts into the sound. Especially in lower case. Also, noise reduction algorithms lose their power if the manufacturer screwed up with the design or used cheap ear pads of insufficient density.


In fact, the idea of ANC is a hundred years old in the afternoon - the first patents were registered back in the 30s of the last century, and the technology itself has long been successfully used in the aviation and defense industries. Since then, it has seriously evolved in technical terms, acquired useful functions and began to be used in other industries. For example, the auto industry. The first car with ANC, which cut off the driver from the hum of the engine and external noise, was the Honda Legend Acura RL luxury sedan. Then similar tricks were adopted by Audi, Cadillac, Ford and Honda.

Noise Canceling Headphones

ENC, DSP, CVC and other active noise cancellation technologies

The term ANC is commonly used in the field of consumer headphones a la AirPods. But there are other subspecies of active noise reduction. For example, gaming headsets often use ENC environmental noise reduction technology, which uses directional microphones to significantly reduce ambient noise levels (up to 35dB) so that players can freely communicate in voice chat.

However, ENC has recently been actively used in the market of inexpensive TWS headphones. And this is logical, because many people consider them as conversational headsets for cycling, sports, etc. For example, in the popular low-cost QCY T13 earplugs, 2 additional microphones are used to capture noise. The lower microphone picks up the user's voice, while the upper microphone picks up noise, after which the processor automatically processes both signals, passing them through ENC algorithms, amplifying the voice signal and suppressing ambient noise. Therefore, even in a noisy environment, you can comfortably talk in them.

Another type of noise reduction is called DSP or “Digital Signal Processor”. This technology is used in headphones, smartphones, smart speakers, studio audio equipment, car entertainment systems, and more. In fact, DSPs are the cornerstone of modern audio products, and they can be used however you like. For example, the DSP processor in Sony 360 Reality Audio headphones is responsible for processing the position of the listener's head in space. So that the 3D sound effect always sounds as intended. And in AirPods Max, the DSP constantly monitors the performance of the headset, trying to constantly optimize the sound for the environment.

If we return to the topic of noise reduction, then DSP processors are most often used to filter speech in a conversational microphone. In general terms, DSP noise reduction is similar to ANC and its forward/backward mics. There are also several microphones that register speech and external noise, then both signals pass through a special DSP processor inside the headphones, which generates a reverse sound wave and levels out the noise according to the anti-phase principle. A DSP-enabled headset is a good option for VoIP or Discord when it's very noisy around.


Clearly hearing the speech of the interlocutor is half the battle, in addition to this, you also need to transmit it in high quality. To do this, most good headphones use additional microphones, some of which pick up speech directly, while the other registers external noise. After that, the incoming signals pass through special digital filters that separate speech and noise, drowning out the latter. Depending on the cost of the headphones and the quality of the algorithm, it can “clean” speech from noise almost perfectly, or during cleaning it can introduce small artifacts into speech, leaving a small part of the noise in the background. Often this thing is called CVC or Clear Voice Capture.

For CVC to work correctly, a whole bunch of algorithms are required that know how human speech sounds and how delicately you need to work with it. Therefore, processing is carried out at several levels at once - the algorithm determines the reference signal-to-noise level, automatically adjusts speech to the desired volume level, applies adaptive equalizers to process the entire voice, as well as specialized filters to remove low-frequency bubbling, sibilants and hissing sounds. Due to this, CVC algorithms are able to effectively suppress echo and noise from the environment.

At the end of 2020, the 8th version of the CVC protocol was introduced. Unlike CVC 6.0, which is most often used in modern headsets, CVC 8.0, thanks to more advanced algorithms, can further reduce ambient noise.

Additional features of modern noise-canceling headphones


Having gone in search of the perfect noise reduction, headphone manufacturers have learned a couple of curious tricks that turned out to be very popular among buyers. The most important of them is the ability to reconfigure the noise reduction so that you can hear certain ambient sounds. Different manufacturers may have different names for these things or differ technically, but the result is plus or minus the same.

So, the first thing is called Talk Through(note: or transparent mode). With it, out-of-phase microphones and the DSP can be put into speech-tracking mode and create a more complex out-of-phase waveform to also cancel out ambient noise, but still pick up human speech. Convenient if you want to listen to music without falling out of society. For example, while you're hanging out at the checkout, waiting for your flight, or exercising with a friend at the gym. The second thing is called Ambient Aware and works on a similar principle. With the difference that the noise canceler is tuned not to speech, but to external loud and high-amplitude sounds like a car signal or the sound of an impact. However, the majority is not limited to these two modes and is looking for the perfect formula.


Most often, they come to a hybrid noise reduction with the possibility of flexible settings in a mobile application. For example, the sensational Samsung Galaxy Buds Pro are equipped with a “smart” ANC algorithm, which allows you to fine-tune the noise reduction. For example, in the metro, set the settings to the maximum, while driving a bicycle, on the contrary, adjust the ambient noise so as not to miss the car horn, and in the conditional reading room of the library, on the contrary, lower the noise reduction threshold to the minimum value, since it is so quiet there.

The critically acclaimed Sony WF-1000XM4 earplugs take customization even further with geolocation. WF-1000XM4 can not only remember several operating modes, but also the places in which you use them - office, coworking, gym or favorite cafe. Also, Sony engineers completely reconfigured the ANC algorithms and equipped the headphones with four Voice Pickup directional microphones at once, which constantly listen to the owner. This is not for spying on the Pentagon, but in order to automatically turn off the music when you are talking to someone and also turn it back on when the conversation is over.

Talk through headphones (talk Thru), Ambient Aware

Conclusion


In 2021, we can safely say that digital noise reduction systems in headphones have almost completely got rid of the sores of the past. They work without surprises, hold a charge for a long time, have useful features and at the same time sound good. At least if we talk about the top algorithms that are used in headphones for 300 - 400 dollars and more. If you are not ready to give such a sum, then most likely you will have to put up with some compromises.

The first compromise is not to expect absolute silence. Noise-canceling headphones still let a small amount of noise through due to poor algorithm design or poor design. It all depends on the specific headphones. Some can multiply by zero even an annoying hum during an air flight or a trip to the subway, but at the same time they will “grab” fragments of human speech from the outside world. In other headphones, the noise canceler itself may make noise. Not the algorithm itself, but the built-in amplifier. Only flagship headphones can do absolute silence.

The second compromise is that most noise cancelers are only effective in the 100 to 1000 Hz spectrum. The fact is that we don’t hear basses below 100 Hz as much as we feel them, and at high frequencies, on the contrary, it’s difficult to repeat the structure of the spectrum, so flagship headphones with reference noise reduction from Sony, Bose and Sennheiser usually use additional tools like DSP bass processing and tweeters or additional microphones that are tuned exclusively to the human voice or background noise.

Well, remember that the same headphones with ANC on and off can sound completely different.