Testing noise canceling headphones. Active noise reduction system in in-ear headphones

Noise for residents of megacities is everywhere. Conversations, the hum of machines, construction tools and equipment, ringing mobile phones, sounds of animals - all this not only pollutes the general background, but sometimes puts psychological pressure on a person.

For example, you are going on a trip or a business trip, but in the transport a baby is crying angrily, a dog is barking, or someone, not really considering those around him, allows himself to speak out about everything that comes to his mind, and even in a raised voice.

If you want to drown out the whining of a crying child, “turn off” other unwanted sounds from your perception, then you will need good headphones. "Good" in this context means that they will have maximum level noise reduction.

The first thing you need to remember about noise-cancelling headphones is the basic way they work: they first block out noise and then let you enjoy yourself. high quality sound.

With that said, here is a list of active noise canceling headphones that deserve your attention and are worth buying. Make your world more harmonious, regulate background noise with these great headphones.

Best of the best: Bose QuietComfort 35

Acoustic noise-canceling headphones from Bose. The renowned brand is synonymous with high-quality sound and superior quality. It is not surprising that it was this world-famous company that introduced the world to unique noise-canceling headphones.

Bose's QuietComfort 35 headphones may be too expensive for most people, but they are by far the most comfortable and effective noise-canceling headphones available. They come in classic black or white, but there are other color combinations available.

The headphones fold into a convenient bag for storage or transportation. Sure, they're not cheap, but the noise-canceling technology developed by Bose has been refined over the decades. It remains the pinnacle in this segment of modern technology.

Best Sound: Monoprice Hi-Fi Active Noise-Canceling Headphone

These aren't the cheapest noise-canceling headphones on the market, but they offer the best combination of performance and price. You can find noise-reducing headphones for as little as 300 rubles, but they are unlikely to work as advertised.

Monoprice Hi-Fi headphones promise great job on noise reduction. Active noise-canceling technology blocks up to 22dB of ambient noise and runs on AAA batteries, promising up to 50 hours of use.

It is equipped with a three-pin remote control that allows you to use them with mobile device or applications. The design itself is pretty boring. There is no Bluetooth compatibility, but when it comes to their main function, in the noise canceling category, these headphones are flawless.

Extend the fun: Bose QuietControl 30

As mentioned, when it comes to noise-canceling technology, Bose is the unrivaled leader. Simply because the company has been working with sound since the 1980s, has vast experience and a lot of proven and new technologies. The company was separately engaged in the development of special equipment for noise reduction.

It is thanks to Bose that we can use the best headphones with optimal noise-canceling properties. But the QuietControl 30 headphones offer more than just high performance, reliability and style.

These in-ear headphones provide high level comfort. Some people find in-ear headphones generally uncomfortable to use for long periods of time, so for those users, we recommend the QuietComfort 35. They're so comfortable that you won't even feel them. In any case, there will be no discomfort. Even if you will be using them for a long period of time.

Best Comfort: Sennheiser PXC 480

When it comes to comfort, the most comfortable headphone design is an over-ear design. These headphones cover the entire ear, extending slightly beyond the shell area, which prevents the pressure that those who wear headphones directly on or inside their ears may experience.

These ear devices are equipped with soft materials that provide additional comfort while reducing noise levels. Durable, durable materials give active noise-cancelling headphones durability and reliability. They also have a unique TalkThrough feature that allows users to communicate without removing the headphones.

Stylish: wireless BOHM Bluetooth

These are fairly small headphones that are affordable for almost everyone. Unlike many other noise-canceling headphones, BOHMs include a rechargeable lithium-ion battery that allows you to enjoy up to 18 hours of sound.

From two high quality stereo speakers you can expect high quality sound with strong bass. As additional bonus The headphones are Bluetooth compatible, meaning you don't need wires. Active headphones come in two equally stylish color tones, but we recommend the brown or gold option for maximum wow factor.

In addition to great features, BOHM headphones offer you amazing comfort. They are equipped with lightweight leather ear cups and a soft headband. There's even an in-line remote control and microphone that allows you to make hassle-free calls on the go. Stress-free listening to music is guaranteed.

Best Sound: V-MODA Crossfade Wireless Over-Ear Headphones

Demon wired headphones V-MODA Crossfade looks like something out of science fiction. The two-tone industrial style will make you look like a DJ from the future. But they're not just stylish.

They sound great. These headphones have a 50mm dual diaphragm driver that delivers crystal clear sound that separates the bass from the mids and highs of the tunes.

These headphones will allow you to connect to wired or wireless network depending on your circumstances. Let's say you have a smartphone without a connector and need wireless headphones, but you're using wired headphones with your work laptop. V-MODA Crossfade can handle both devices, and you will be able to sync the headphones with two devices at the same time if you are using your phone and tablet at the same time.

These headphones can stream music wirelessly for about 12 hours on a single charge. But you can still use them wired if the battery dies. The headphones are available in black, chrome, red, and white colors.

Boost Sound: Paww WaveSound 3 Bluetooth

WaveSound 3 headphones are designed primarily for travel. They are equipped with a travel case and special structural elements designed for airplane flights or train travel.

They include an aircraft adapter designed to connect to certain in-flight surveillance systems. They block out cabin noise, eliminating up to 23 dB of unwanted outside noise. In addition to clear sound reproduction and noise cancellation, WaveSound 3 has a built-in microphone for calls (please don't do this on a plane!).

The lightweight and durable metal design will fit comfortably on your head. Sound connoisseurs say the WaveSound 3 headphones do a great job of canceling out noise, delivering great sound to their favorite songs, especially when traveling by train.

Best Design: AKG N60 Headphones

Portable, lightweight and attractive design The AKG N60 headphones are ideal for those on the go. Thanks to 30 hours battery life And USB charging This device will appeal to those who do not sit still.

The AKG N60 is made of plastic wrapped in high-quality leather that extends to the ears. Active noise cancellation is present, but the real appeal of these headphones is the sophisticated design. The audio highs have very clear mids, and the lows have great depth and detailed bass.

Bottom line

All of these models offer varying degrees of noise reduction, but always perfect sound and user friendliness. Choose your type of headphones, download great songs, and fill your world with your sound.

Here you are, do you like silence? - And I love it. It’s not even the silence itself, but the absence of external stimuli. While studying or working, you need to focus on the problem/task at hand, and it’s quite difficult to do this when your household is dancing around you or the phone is ringing all over the office... Of course, there are moments when you seeth with particular passion over your work, when you are already drawn into process and nothing can distract you. But what to do when there is no particular desire to do the work, and it’s also impossible to concentrate? For myself, I found a solution in headphones with an active noise reduction system.

Let's start with the fact that I first learned about headphones with an active noise reduction system after reading here
, where hackers actively shared photos and discussed their jobs. The author of that thread mentioned the rather expensive Bose QC-15 headphones (~$500 in the CIS), so an operation was launched to find cheaper alternatives. As a result, the choice fell on Audio-Technica ANC7b - headphones from a well-known Japanese manufacturer that has proven itself all over the world.

▐ Technical specifications

▐ Design, construction, comfort of wearing

▐ Sound, compatibility, some aspects of operation

frequency response

As for the sound quality itself, which is actually a purely subjective concept and ideally I would listen to IRL headphones before buying, I’m a little more than satisfied with the sound. I use headphones mainly at home, paired with an external DAC, so in both modes I do not feel a lack of volume. Moreover, I use it quite often - at least 3-5 hours a day and often with noise reduction turned on (+ sounds of nature or light music). This set makes it possible to completely ignore the roar of the old refrigerator, the conversations of roommates and their movements around the room. At the same time, more loud conversations leak, which for me personally is a plus.

If it were not for such huge sizes (on my already small head, such headphones look very deplorable), I would gladly ride with these headphones in the subway. The bottom line is that ANC works best with lower frequencies, i.e. the rumble of the metro is completely cut off, and female voice The station announcement remains audible (provided you are listening to an audiobook/podcast or music at low volume). One of the main drawbacks was also noticed here: due to the use of active electronics, the device tends to pick up interference from mobile phones, albeit periodically, but this effect causes some discomfort.

▐ Active noise reduction system design

Active noise cancellation, in turn, requires the introduction of electronics into the headphones. The operating principle of this system is quite easy to understand, even if you skipped physics classes at school. Sound is a physical phenomenon that is the propagation of elastic waves in a certain medium. More precisely, sound is a wave. Music, the sound of a jackhammer, the screams of a baby - these are all sound waves that we encounter everywhere. One of the main phenomena inherent in waves is interference.

Wave interference is a mutual increase or decrease in the resulting amplitude of two or more coherent waves when they are superimposed on each other.(c) Wikipedia

▐ Internals, autonomy

▐ Price, results

Advantages and disadvantages

Today's market is represented by thousands of headphone models: from cheap Chinese NoName earplugs to exclusive Final Audio Design, costing more $8 000 . Prices are driven by customer needs and technology. Today we will talk about the active noise reduction technology installed in most closed-type headphones, and most importantly, we will find out the causes of headaches when listening to such “ears” for a long time.

Active noise reduction system. History and operating principle

Music has long become man's most reliable companion. For any mood, state, emotions and experiences there is always a melody that can warm the soul, heart and thoughts. Manufacturers started thinking about portable music back in the middle of the last century. In 1979 the company Sony introduced the first portable cassette player Walkman TPS-L2. Several decades later, this development was recognized as one of the company's greatest inventions. In 1984, the Japanese manufacturer, keeping up with the times, released the first CD player Sony Discman D50. In the summer of 1998, the first MP3 player burst onto the market - MPMan F10, with a capacity of 32 MB. And all this time, the evolution of players was accompanied by the development of guarantors of quality and good sound– headphones.

The history of the development of the active noise reduction system (hereinafter - SAS) begins in the distant 1934 when the inventor Paul Lug receives a patent describing the principle of canceling sinusoidal signals emitted by a loudspeaker. In 1950 Lawrence Vogel pioneers the use of noise suppression systems in helicopter cockpits and aircraft cabins.

I got to SAS headphones back in 1957 year when Willard Meeker on the presented working model on-ear headphones managed to cut off the noise on sound range from 50 to 500 Hz. The first one production model headphones with active noise reduction system was presented by the company Bose in the late 80s and was used in aviation.

Bose Quiet Comfort: the beginning

The operating principle of SAS, from a physics point of view, is very simple. Any sound is represented by a wave, which means you can create it mirror image– an inverted wave that will completely extinguish the original one.

The headphones, equipped with an active noise reduction system, contain microphones. Their task is to measure the level of ambient noise. The sound signal received from the outside is converted into an inverted wave and transmitted to the main speaker. The new wave is active in antiphase(minus the useful signal - music) to noise and, thus, reduces its sound to zero.

Headache

It would seem that the use of active noise suppression technology should significantly improve the life of avid music lovers who cannot imagine going to work, walking or outdoor activities without on-ear headphones wrapped around their heads, musical drive and rhythm. The number of models equipped with SAS is valid. There are a wide variety of headphones on the market. price categories and form factors: from inexpensive compact plugs to heavy studio monitors. The noise reduction system is improving every day, the quality of music playback is increasing, manufacturers are finding new and new marketing solutions to popularize headphones with the system Noise Canceling. But there is a category of people who, for all their positive attitude towards portable sound, is forced to abandon all the technological advantages of “perfect headphones” for one simple reason - intolerance to the active noise cancellation system.

The realities of today's market are significantly different from those of just 10-15 years ago. Before going to the store, the buyer carefully studies the reviews, reviews and re-reads a dozen or two reviews, and only then decides to buy.

Among the reviews devoted to the category of headphones with an active noise reduction system from such famous brands as Sony, you will find many positive aspects. Yes, manufacturers have really done a lot to ensure that the headphones not only sound good, but also fit comfortably and have an interesting design. Read the lines more carefully and you will see that a small percentage happy owners complain of constant headaches and nausea when wearing headphones with SAS. What are these – customized reviews from competing parties or a reality that not everyone faces? So why, when using seemingly perfect headphones that allow you to enjoy crystal clear sound without extraneous noise, does your head start to hurt?

Reason one: when the sea is rough.

If at least once in your life you have had to experience all the bitterness of a deplorable condition, which is accompanied by seasickness, I hasten to upset you. You may be in the unlucky category 5-7% people for whom headphones with active noise cancellation will remain a useless technological breakthrough.

Seasickness and headaches caused by ASP headphones have a lot in common. At the moment when a person is calmly resting in a ship’s cabin, the brain understands that the body is at rest. At the same time, the ship is constantly rocking on the waves and this movement is captured by our internal accelerometer - vestibular apparatus. The endolymph moving in the ear canal irritates the nerve endings, which send an impulse to the brain, making it clear that the body is in a state of movement. But you are reclining in an armchair in a cozy cabin!

By putting on headphones with active noise cancellation and going outside, you are, without realizing it, deceiving your brain. Passers-by approaching, a noisy highway, the hum of wheels, a sharp wind - the organs of vision clearly paint a picture of the fact that you are on the street. But the hearing organs indicate complete silence. This discrepancy confuses the brain. Alas, a headache is guaranteed.

Reason two: monotonous stimulus.

Having understood how active noise cancellation works, Grandfather Newton would have said the following: “Force is acted upon by a counterforce.” Such a sound battle and interference process as a result, it achieves the desired result - we eliminate unnecessary ambient noise and can completely immerse ourselves in the music.

There is just one “but”. As a result of this constant noise suppression, monotonous sound waves act on the eardrums. This does not mean that we should hear a hum or any extraneous noise. The brain perceives exclusively the variety of sound tonics of a particular audio recording or track, but nervous system... The effect of such vibrations is the principle that works at the basis of the active noise reduction system and, alas, it is impossible to predict which organism it will lead to nausea and headaches.

Reason three: silence is not always calm.

In research institutes and laboratories involved in the study of sound and sound waves, there are so-called “absolutely quiet rooms”. They are designed in such a way that they allow you to block up to 99,9% all noise. It is in such premises that high-quality and expensive products are tested. audio equipment world famous brands.

Imagine that you find yourself in such a room. After a few seconds, you will begin to hear the squeak of a mosquito. A few minutes later - a rumbling stomach and a pounding heart. Five minutes of being in absolute silence will begin to create a state of anxiety and excitement in the body. Not a single person could stand more than 45 minutes in such a room.

Despite the fact that when listening to music on headphones with an active noise reduction system, absolute silence is out of the question, the very principle of ASH operation intersects with that very “absolutely quiet room”. People whose bodies are not adapted to this type of headphones will experience headaches and nausea through 1.5 – 2 hours operation.

Reason four: bass is my enemy

Depending on the height, everything audio frequencies When equalizing, it is customary to divide into: high, medium and low. The active noise suppression system does its best job of cutting out low frequencies, which are what predominantly saturates the street noise around us. The situation is worst with high frequencies, since there is a risk of suppressing the useful sound signal represented by the music.

Mirror sound wave, reproduced in antiphase in order to suppress ambient noise, is most saturated precisely low frequencies. Low Frequencies cause maximum vibrations when exposed to liquid, and if we take into account the fact that the human vestibular apparatus is filled endolymph, then the constant vibrations from the booming bass cause headaches.

Reason five: design flaw

Another reason why the owner of headphones with an active noise reduction system may constantly experience headaches is that the headband is too tight. However, this common problem on-ear headphones and SAS itself can hardly be blamed for this.

The design feature of any on-ear headphones is an elastic headband that should hold them on the head. Constant voltage on the temporal zone leads to increased pressure. After a few hours of using such “tight” headphones, headaches and nausea occur.

How to avoid useless purchases

Of course, headphones equipped with an active noise reduction system have a number of advantages: comfort when listening to music, a high level of sound detail and a safe volume level. Alas, it is impossible to predict exactly how your body will react to SAS. Before you give away your hard-earned money, and then, literally, do not complain about the headache, try to borrow headphones equipped with ASP from friends or acquaintances. Remember, to understand whether SAS really has a negative effect on your condition, you need to listen to headphones for more than 2-2.5 hours.

Having bought the model of headphones you like, which is called “without looking”, according to Article 502 Civil Code of the Russian Federation and article 25 Law of the Russian Federation of February 7, 1992 No. 2300-1 “On the Protection of Consumer Rights”, you have 14 days to return goods that do not fit “in style, color or dimensions”, subject to all storage conditions. To avoid disagreements and refusals to return, before purchasing, re-read the above articles and consult with a consultant at a particular store.

4.75 out of 5, rated: 8 )

The life of a city dweller is full of stress. Therefore, when coming home, every city dweller strives for maximum comfort and silence. But, alas, if comfort is still achievable, then hiding from the noise of the metropolis is not so easy. And, to be honest, many modern high-rise buildings do not have good sound insulation. Many people are familiar with the feeling of “kinship” with their neighbors, which arises from the fact that all the ups and downs of their lives are often heard better than a TV show.

Traditional methods of getting rid of street noise were still considered to be plastic double-glazed windows, and for internal noise insulation - sound insulation of walls, floors and ceilings with special building materials. This applies to this day, but hasn't modern science come up with something else? Let's look at the best innovations for the city in the field of devices for active noise suppression in the apartment.

Radio-electronic jammers

Our musical tastes do not always coincide with the tastes of our neighbors. Loud music or a screaming TV is the bane of many apartment buildings. If one likes it, everyone listens. And if the neighbors are also karaoke fans, the problem becomes even more acute. Alas, unfortunately, these “musical” people do not always adequately respond to requests to “turn it down.” Well, if you can’t come to an “amicable” agreement, and your nerves are already on edge, you have to take radical measures. And for this it is not necessary to involve law enforcement agencies.

There is a way to fight effectively on your own. To do this, you can use an electronic jammer (in common parlance, a “jammer”).

You can either purchase such a device or make it yourself. On the Internet you can find a lot of diagrams, following which you can make these electronic jammers. The schemes can be either simple or quite complex, but the principle of their operation is essentially the same.

Operating principle of radio frequency suppression device

A device whose task is to silence the work electronic devices, is a signal generator in the same frequency range as the frequencies of the jammed devices, only in antiphase. The signals generated by the device do not carry any information, they are simply “white noise”. Therefore, before purchasing a device, you must first determine the frequency range in which this device operates. The meaning is simple - if the frequencies do not match, the device will not perform its function.

The effect of the “jammer” is as follows: the “useful” signal from the neighbors’ electronic device is replaced by “white noise”, which, in general, is what the user of such a device needs.

After the frequency range, the second important characteristic of a jammer is its range. The distance over which the radio frequency “jammer” effect operates depends on many factors: where the device is used - outdoors or indoors, what the weather is like, etc.

Jamming electronic devices is not a myth.

But it should be remembered that the use of “jammers” is illegal, so they must be used with caution and should never be abused.

A similar device for suppressing noise in an apartment can be purchased in various online stores. The price ranges from several thousand to several tens of thousands of rubles (depending on the power of the device and the range of frequencies covered).

Noise suppression device in the Sono apartment

This system was developed by the Austrian industrial designer Rudolf Stefanich. It is based on the same technology that is used in headphones. This small device is attached to the window using special suction cups and absorbs most of the extraneous sounds coming from the street.

The device kit consists of a microphone, speaker and built-in processor. A speaker pressed against the glass uses it as a resonator and reproduces sounds in antiphase.

The built-in processor analyzes and filters sounds received through the microphone. This technology allows the device to selectively suppress noise based on user settings.

Why is this necessary? Very simple. You can, for example, block out the noise of cars and utility vehicles, but set the device to allow the sounds of chirping birds and rustling leaves to pass through.

In addition, the Sono system itself will be able to reproduce a variety of pleasant sounds: the singing of whales, the rustling of the forest, the sound of the surf, and the like.

In 2013, this concept project made it to the finals of the James Dyson Award. Unfortunately, it is currently impossible to buy this device, since the Sono currently only exists as a prototype.

Active Noise Cancellation System

An effect similar to what we described above (the Sono system) may someday be achieved by an active noise reduction system. Acoustic engineers from the Technical University of Berlin propose to dampen user-selected street sounds inside the frame using compact loudspeakers mounted between the glass frames.

The operating principle of this system is similar to Sono (“unnecessary” sounds are canceled out by the same sounds emitted in antiphase).

German experts believe that their system can be used not only in residential and administrative premises, but also in cars and airplanes.

On at the moment The system is under development, so more detailed information missing from it.

Overseas inventors also did not stand aside. San Francisco-based Celestial Tribe has offered its Muzo noise-canceling device, which can also provide privacy by creating a so-called “bubble of silence” around interlocutors.

Muzo looks like a small speaker that cuts out unwanted sounds from the user.

The gadget is mounted on a flat surface that serves as a resonator and reproduces sounds that remove extraneous noise. In addition, the device is able to dampen external vibrations, for example, from nearby construction. The device itself can also play pleasant sounds, for example, to improve sleep.

Unlike devices 2 and 3 on our list, Muzo may soon go on sale. Having started on Kickstarter in the summer of 2016, the developers raised more than four hundred thirty thousand dollars (with a planned one hundred thousand). In this regard, pre-orders have already begun on Indiegogo.

According to various sources, this active noise absorber in an apartment or office will reach its first owners in January-February 2017, and its cost will range from 119 to 159 US dollars.

This example demonstrates the use of adaptive filters to attenuate acoustic noise in active noise reduction systems.

Active noise cancellation.

Active noise control systems are used to attenuate unwanted noise propagating through the air using electro-acoustic devices: measuring devices(microphones) and signal exciters (speakers). The noise signal usually comes from some device, such as a rotating machine, and it is possible to measure the noise close to its source. The purpose of an active noise reduction system is to create an "anti-noise" signal using an adaptive filter that will attenuate the noise in a specific quiet area. This problem differs from conventional adaptive noise reduction in that: - the response signal cannot be immediately measured, but only its attenuated version is available; - when adapting, the active noise reduction system must take into account the secondary signal propagation error from the speakers to the microphone.

The tasks of active noise reduction are discussed in more detail in the book by S.M. Kuo and D.R. Morgan, "Active Noise Control Systems: Algorithms and DSP Implementations", Wiley-Interscience, New York, 1996.

Path of secondary spread.

The secondary propagation path is the path that the anti-noise signal travels from the speaker output to the error-measuring microphone located in the quiet area. The following commands describe impulse response speaker-microphone path with a limited band of 160-2000 Hz and a filter length of 0.1 s. For this active noise reduction task, we will use a sampling rate of 8000 Hz.

Fs = 8e3; % 8 KHz N = 800; % 800 counts at 8 kHz = 0.1 second Flow = 160; % lower cutoff frequency: 160 Hz Fhigh = 2000; % high frequency cutoff: 2000 Hz delayS = 7; Ast = 20; % suppression 20 dB Nfilt = 8; % filter order % Create a bandpass filter to simulate a band-limited channel% bandwidth Fd = fdesign.bandpass("N,Fst1,Fst2,Ast" ,Nfilt,Flow,Fhigh,Ast,Fs); Hd = design(Fd,"cheby2" ,"FilterStructure" ,"df2tsos" ,... "SystemObject" ,true); % Noise filtering to obtain channel impulse response H = step(Hd,); H = H/norm(H); t = (1:N)/Fs; plot(t,H,"b" ); xlabel("Time, s" ); ylabel( "Odds values"); title( "Impulse response of the secondary signal propagation path");

Determination of the secondary route of spread.

The first task of an active noise reduction system is to determine the impulse response of the secondary propagation path. This step is usually performed before noise reduction using a synthesized random signal played through the speakers in the absence of noise. The commands below generate random signal lasting 3.75 s, as well as the signal measured by the microphone with an error.

NtrS = 30000; s = randn(ntrS,1); % random signal synthesis Hfir = dsp.FIRFilter("Numerator" ,H."); dS = step(Hfir,s) + ... % random signal passed through the secondary channel 0.01*randn(ntrS,1); % microphone noise

Create a filter to evaluate the secondary propagation path.

In most cases, to adequately control the algorithm, the response duration of the filter estimating the secondary propagation path must be shorter than the secondary path itself. We will use a 250 order filter, which corresponds to an impulse response of 31 ms. Any adaptive FIR filtering algorithm is suitable for this purpose, but the normalized LMS algorithm is usually used due to its simplicity and robustness.

M = 250; muS = 0.1; hNLMS = dsp.LMSFilter("Method" ,"Normalized LMS" ,"StepSize" , muS,... "Length" , M); = step(hNLMS,s,dS); n = 1:ntrS; plot(n,dS,n,yS,n,eS); xlabel("Number of iterations"); ylabel( "Signal level"); title( "Identification of a secondary propagation path with the NLMS algorithm"); legend( "Expected signal","Signal Output","Error signal" );

Accuracy of the resulting estimate.

How is the impulse response of the secondary path accurately estimated? This graph shows the coefficients of the real path and the path calculated by the algorithm. Only the end of the resulting impulse response has inaccuracies. This residual error will not harm the performance of the ANC system while it is working on its selected task.

Plot(t,H,t(1:M),Hhat,t,); xlabel("Time, s" ); ylabel( "Odds values"); title( "Determination of the impulse response of the secondary propagation path"); legend( "Valid", "Evaluated" , "Error" );

The main path of signal propagation.

The noise path to be suppressed can also be described using a linear filter. The following commands generate an impulse response of the noise source-microphone path with a limited bandwidth of 200-800 Hz and a response time of 0.1 s.

DelayW = 15; Flow = 200; % lower cutoff frequency: 200 Hz Fhigh = 800; % upper cutoff frequency: 800 Hz Ast = 20; % suppression 20 dB Nfilt = 10; % filter order % Create a bandpass filter to simulate impulse response with % limited band Fd2 = fdesign.bandpass("N,Fst1,Fst2,Ast" ,Nfilt,Flow,Fhigh,Ast,Fs); Hd2 = design(Fd2,"cheby2" ,"FilterStructure" ,"df2tsos" ,... "SystemObject" ,true); % Noise filtering to obtain impulse response G = step(Hd2,); G = G/norm(G); plot(t,G,"b" ); xlabel("Time, s" ); ylabel( "Odds values"); title( "Impulse response of the primary propagation path");

Noise suppression.

A typical application of active noise cancellation is to muffle the sound of rotating machinery due to its irritating properties. Here we will artificially generate noise that could come from a conventional electric motor.

System initialization.

The most common algorithm for active noise reduction systems is the LMS algorithm with additional filtering of the filter output signal before generating an error signal (Filtered-x LMS algorithm). This algorithm uses secondary propagation path estimation to calculate an output signal that is destructive to unwanted noise in the error measurement sensor area. The reference signal is a noisy version of the unwanted sound measured close to its source. We will use a controlled filter with a response time of about 44 ms and an adjustment step of 0.0001.

Simulation of the developed active noise reduction system.

Here we will simulate the operation of an active noise reduction system. To highlight the difference, noise reduction will be disabled for the first 200 iterations. The sound on the microphone before suppression represents the characteristic “howl” of industrial motors.

The resulting algorithm converges approximately 5 s (simulated) after turning on the adaptive filter. Comparing the spectra of the residual error signal and the original noisy signal, it can be observed that most of the periodic components were successfully suppressed. However, the effectiveness of stationary noise reduction may not be uniform across all frequencies. This often happens in real systems, used for active noise control tasks. By listening to the error signal, the annoying “howling” is significantly reduced.