XIV Международная студенческая научная конференция Студенческий научный форум - 2022

The variety of technologies and terms makes it difficult for users to choose headsets. The purpose of this article is to discuss the basics of noise reduction and to compare different methods.

What is the difference between the active and passive noise canceling in headphones and headsets? Passive and active noise canceling technologies are widely used in both consumer-grade headphones and professional headsets for contact centers and offices. What is the difference between headset noise reduction techniques, and what is the most effective noise cancellation method? The difference is the active and passive noise canceling headphones. The general term noise cancellation refers to several ways to reduce the effect of unwanted noise on the sound quality of headphones and headsets. Manufacturers of these audio devices use different noise reduction technologies - active (with static and adaptive filters), passive, and hybrid.

What is Active Noise Cancellation? Active Noise Cancellation (ANC) is a process that uses a microphone to monitor and filter ambient noise in headphones. Active noise cancellation is achieved by using analog or digital filters and differs in implementation types - closed-loop, open-loop, and hybrid noise cancellation. High quality active noise canceling technology significantly improves the acoustic performance of headphones and headsets with good passive noise canceling. But it cannot compensate for design flaws or poor material of the ear cushions, if the manufacturer decided to save on them. Typical example of an active noise canceling headset is Poly Savi W8220 wireless headset.

What is Passive Noise Cancellation? It is what the design and materials of earbuds and headsets are all about, be it the silicone earbuds of the vacuum headphones or the soft ear cushions on the on-ear models. Basically, it is the level of isolation from external noise that a device can provide on its own, without considering electronic components and algorithms. Simply put, this is how well the earbuds do the earplug function. Good passive noise cancellation is, first of all, high-quality materials and a well-thought-out design of the ear cushions. Poly Voyager 8200 UC headset is an example with advanced passive noise cancellation; General noise suppression and Total noise cancellation (the cumulative effect of noise cancellation that the end user hears) is the sum of passive and active noise cancellation. This set is determined by the features of the electronic components of active noise cancellation, as well as the design and material of the ear pads (passive noise cancellation).

As mentioned, there are three types of active noise canceling: open loop, closed loop, and hybrid (a combination of the first two). Open-loop ANC uses the main microphone to track external noise, then converts it to anti-noise and mixes it with the playback audio to provide noise cancellation. This process is rather complicated, since the phase inversion of complex signals must take into account the delays in the passage of noise and calculate the noise protection signal so that it comes to the user simultaneously with the noise.

Adaptive noise reduction is based on the ability of filtering algorithms to detect and adapt to different noise patterns. Implementing ANC with feedback presents some challenges as it is difficult to design a system that will always remain stable due to the need to fit the size of the headphones, and also due to the tendency of the feedback loop to drive the system to excitement. Feedback requires a microphone on the outside of the earbuds to track the sound coming to the user. By comparing the sound coming to the user with the audio source, the feedback algorithm identifies the noise and creates protections that help suppress it. The closed-loop system is mainly effective for suppressing low frequencies. The reason is that there is a possibility of suppression of a part of the useful signal, which can be recognized as noise. This results in coloration or distortion of the original signal.

The hybrid ANC solution combines the best of the techniques listed above. It uses an external main microphone to track ambient noise and an internal microphone to monitor for error and track what the user hears in addition to the audio being played. When both methods are used at the same time, noise cancellation is as effective as possible.

Until recently, manufacturers have only used static, non-tunable active noise suppression filters. This universal method assumes that one filter works for all sound reproduction conditions.

ANC today uses adaptive or tunable filters that adapt to a person's hearing or headphone configuration and adapt to changing acoustic environments. This improves the noise reduction function for a wider range of users. How ANC works with adaptive filters Adaptation is not just noise filtering. If you analyze the ambient noise, you can see a lot of its varieties, for example, the sound of engines in the cabin of an airplane (low frequencies), conversations in a cafe (medium frequencies), music at a concert (very loud sound) and noise in the library (very quiet sound). In any given situation, the adaptive filter works to maximize the overall noise reduction performance. For example, in the cabin of an airplane, a filter suppresses lower frequencies, while in a cafe - mids, etc. In reality, the adaptation process is more complicated, but our description gives a general idea of ​​the capabilities of adaptive filters.

The challenge in developing a high-quality noise reduction solution is the need to adapt it to the anatomy of the auditory tract of thousands of users. In the simplest case, active noise cancellation is described as noise inversion. In reality, when creating a suppression system, it is necessary to take into account the travel time of noise from the main microphone to the eardrum. If the ANC system does not correctly model the noise path, the protection it provides will be inaccurate and may even amplify the noise. This is the risk of using universal static filters. An adaptive filter uses a microphone to control errors or the proportion of noise in the desired signal, which allows you to more accurately simulate what the user hears. This allows the system to adapt or rearrange the filters to provide the best noise protection for that particular user in a particular acoustic environment.

The advantage of the adaptive noise cancellation system is that it takes into account the unique physiological characteristics of each user. In addition to this, the adaptive solution can track the actual noise and adjust filters based on its type to make the suppression as effective as possible. Until relatively recently, only isolating vacuum or on-ear headphones were supplied with tunable filters for noise suppression. Today, even non-isolating headphones can be equipped with adaptive noise cancellation technologies, as modern algorithms are able to compensate for various distortions arising from poor passive isolation. Adaptive solutions sound better than closed-loop systems because they do not create unwanted coloration in the sound. Active noise canceling professional headsets dramatically improve the efficiency of call center agents as well as mobile office workers. These headsets protect workers from unwanted noise in the challenging acoustic environments found in open-plan offices or on the road.

Bibliography:

How Do Noise-Cancelling Headphones Work: Active, Passive, Adaptive - Treblab.com – Treblab Blog

The Technology Behind Noise Cancelling Headphones: How It Works - Headphonesty

Passive Noise Isolation vs. Active Noise Cancellation – Ultimate Ears

Active Vs. Passive Noise-Canceling Headphones: Differences Explained (screenrant.com)

Active vs Passive Noise Cancelling [2021 Answer] - Earbuds Zone