Biography

Abstract

Introduction

Noise is a complex of sounds, which causes the unpleasant feeling or sickly reactions. Noise - one of forms of physical environment of life.

Noise influences different people differently, it can depend on different factors, such as acoustical sensitivity of the person, duration of action of noise.

Noise disturbs to normal rest, restoration of forces, causes diseases of organs of hearing, promotes increase in number of other diseases badly operates on mentality of the person

Noise - the same slow murderer, as well as a chemical poisoning. The first that complaints to noise have reached us it is possible to find at the Roman satirist Juvenala (60-127).

But despite all lacks recently noise is included more and more into our life, at the enterprise, in streets, at home. Ever less places remains, where actually it is possible to stay in silence

Noise level in 20-30 decibels (dB) almost harmless to the person. It is a natural noise background without which the human life is impossible. The sound in 130 decibels (an equivalent of work of the jet engine of the plane) already causes painful sensation in the person, and in 150 - becomes for it intolerable. The sound in 180 decibels causes weariness of metal, and at 190 rivets from designs are pulled out. Not without reason in average centuries there was a death penalty "under a bell <". The bell ring slowly killed the person.

Any noise of sufficient intensity and duration can lead to different degree of decrease in acoustical activity. In table 1 various noise levels and their equivalents

Sound-level, dB	Description	Analogy
160	Hum which a man does not maintain	Airplane at flight
90	Loud sound	Scream
70	Noise which it notices	A loud talk is in 5 meters
50	Noise which does not cause inconveniences	A low talk is no more than 3 meters
45	Practically not heard
40	Very quiet sounds	A talk is 10 meters in the distance
30		Whisper, distinguished from distance 5 meters
25	Sound which a man does not notice	Quiet garden

Actuality

Acoustic noise which surround us, harmfully influence the person in all spheres of a life, therefore a question noise-suppression, especially now, has very much great value

There are two ways of the decision of this problem: active and passive. Passive methods consist in installation of passive obstacles for passage of a sound wave, such as: detonation of trees, near to road, installation of windows with noise-suppression, an upholstery of walls sound-proof materials, etc. such methods can be effective enough in certain cases, depending on a site of such obstacles and a noise source.

Unlike passive methods noise-suppression, active methods work by a principle - to measure noise (an unpleasant sound), having processed its tax a sound (more often the inverted sound wave) on reproduction system therefore noise develops with the inverted noise and there is a noise suppression. Depending on characteristics of noise, its intensity, an arrangement of sources noise-suppression, the percent приглушения noise varies. Active systems noise-suppression in the main turn are characterised by mobility, настраиваемостью, simplicity of installation, in comparison with passive systems

Decisions in the world

Today in in the world there are many different systems of suppression of noise, for example the British engineer from University Hadersfild – Selvin Right has developed "the silence Car" (Sіlence Machіne) which by means of microphones catches and analyzes noise, after processing submits on dynamics therefore noise is compensated. In cars премиум a class, such firms as Tayota, Honda establish systems which suppress noise of the engine of the car.

Such systems have found Wide popularity in the big airports where that in the airport it was not audible loud engines of planes, establish systems noise-suppression which are capable to muffle a rumble of the plane which moves directly near a premise.

One more area where there were systems noise-suppression - ear-phones. These are active ear-phones which the microphone is built in, and the sound in ear-phones mixes up with the inverted sound of environment, compensating it. But these devices are yet accessible to everyone because of their big price.

Practical value of job performances.

In frameworks магистерской works will existing methods noise-suppression are considered and analysed and developed new for work in a usual conditions of life, at presence only the computer, columns and a microphone

Statsionarnost means that properties of noise (capacity, spectral structure) do not vary in time. Constant hissings of a microphone or intensifying equipment, a rumble of the electric system, motor vehicles which pass, noise from the working system block, etc.

Physical view of sound

A voice signal by nature is formed by the transition of clot and discharging of air. The simple mechanical model of moving of sound in space is rotined on a picture 1.

Pic. 1. A mechanical model of moving of sound is in space

This model shows simple model of physical moving of sound waves in space, as for example air. We address to a golf sphere, for example a golf sphere, has incorporated together by means of a spring. The golf sphere is represented by weights of molecules in a real material, and the spring represents intermolecular forces between them. If the golf sphere eventually is pushed in a direction of the last, then a spring which connects it with a following sphere, will be reduced and will push.

The analysis of methods of digital processing of digital signals and methods of active noise-suppression.

Рис. 2. Principle of work of algorithms of active noise-suppression.

Today in each computer there is a sound card with which help the sound is entered in the computer and is deduced from it

Each sound card consists of two basic components: ADC (analogue-digitizer) and DAC (the digital-to-analogue converter). By means of ADC, sound signals which act in film a microphone or other device they оцифровуются and arrive in a sound card in the form of discrete readout which then can be counted and process. DAC necessary for return transformation - discrete readout which arrive on a sound card are transformed to an analogue signal which then arrives on amplifiers and on dynamics. Also except the basic components a sound card contain many auxiliary devices that give the chance to the developer to use it in full. Some sound cards are equipped by the special processor which does a compression, for example decoder MP3, different sound effects, at necessity, such as reverberation, an echo, etc., in this case say that the payment contains the hardware decoder. If the sound card is not equipped by the hardware decoder its obligations are incurred by the central processor then such decoder is called as program.

Numbering and signal installation becomes by means of the theorem of Kotelnikova according to which the analogue signal which has the limited spectrum can be established unequivocally and without loss given (discrete readout), taken c frequency twice большей, than the maximum frequency of a spectrum.

After digitization a signal yet годен for digital processing, it still it is necessary квантувать. Unlike digitization at quantization there is an information loss, this loss is called as quantization noise. It is natural that the more quantization degrees, the quantization noise there is less, it is considered that at sixteen-bit tsifro-anologovom transformation the human ear does not hear quantization noise. Together digitization and quantization name analogue-digital transformation or pulse code modulation (PCM).

After reception of sequence of readout with them it is possible to work, processing, transforming. At this stage transformation of Fure which allows to translate the time form of a signal in frequency, and on the contrary is actively used. The frequency form of a signal contains the information on available frequencies in a signal, their phase and amplitude. It gives the chance to process freely the data not only at level of all signal, but also at level of separate frequencies. After transformation, processing, if necessary given (readout) it is possible to deduce resultants on columns, having carried out return procedure - digital-to-analogue transformation

Methods active noise-suppression different enough also use various hardware base, but mostly many of them use similar algorithms which are based on signal inversion.

Modern systems приглушения noise use two main principles which application depends on a noise source, and obstacles which it takes place. The most widespread principle is by means of an acoustic anti-wave which suppresses noise with which develops. The second, more difficult method in respect of hardware realisation - by means of vibration, such method has found recently the application in such systems as systems "Active noise-suppression in central airs of inhabited and industrial premises" which are already used in some places, and also in this direction have begun workings out of glass which will vibrate in an antiphase to street noise, for it the processor which accepts answers, processes and gives out the information.

In connection with fast development of the industry in the world appears more and more systems which are capable to suppress noise, in all of them there are the positive and negative qualities, scopes. But all these systems now are not accessible to everyone because of the main reason - their costs, therefore are necessary systems and algorithms which will suppress noise in a life with the help of technics which now accessible practically everywhere - the computer, a microphone, columns

Conclusion

Systems active noise-suppression are very various and have different complexity, but having analysed even the most simple method of suppression - signal inverting in time - it is possible to see positive and negative sides.

Its simplicity and speed concerns positive sides - it is necessary to invert only discrete readout in time representation of a signal and a tax on an exit, are absent ресурсоемкие transformations of Fure. As a result the algorithm becomes less exacting to computer resources that also will affect cost of hardware base of system шумоподавления or its efficiency, at presence not the powerful computer

Different efficiency concerns negative sides on different frequencies, the big dependence on a relative positioning of a source of noise and a source of a signal of suppression, dependence on frequency characteristics динамиков (sources of a signal of suppression).

But also the greatest plus is possibility of wide application of such systems in a life because all work carries out the computer which now is practically everywhere and its price, in a good complete set, not so big

Additional researches in this area will allow to develop system of effective active suppression of noise which can be used in a life, at the enterprises, everywhere, where there is a necessity to extinguish стацианарные noise, using simple, mobile system.

Literature

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