Linguistic signals first said to be composed of some units which are divided into significant and non - significant ones. The relationship between all the units or elements of a language includes different notions starting from sounds, morphemes, words word combinations and ending up with phrases. The scientific study of a language involves an explanation of a mass of notions in terms of a rigorously organized and highly patterned system - the link between the units. The whole system of relation of linguistic units forms a system of a language. The character of a system, or the way this system works explain the structure of a language. All languages differ in systems and structures.

Phonetics is concerned with the human noises by which the thought is actualized or given audible shade: the nature of these noises, their combinations, and their functions in relation to the meaning. Phonetics studies the sound system of the language, that is segmental phonemes, word stress, syllabic structure and intonation. It is primarily concerned with expression level. However, phonetics is obliged to take the content into consideration too, because at any stage of the analysis, a considerable part of the phonetician's concern is with the effect which the expression unit he is examining and its different characteristics have on meaning.

Only meaningful sound sequences are regarded as speech, and the science of phonetics, in principle at least, is concerned only with such sounds produced by a human vocal apparatus as are or may be earners of organized information of language.

Consequently, phonetics is important in the study of language. An understanding it is a prerequisite to any adequate understanding of the structure of working of language. No kind of linguistic study can be made with but consonant consideration of the material on the expression level.

It follows from this, that phonetics a basis brunch or fundamental brunch of linguistics. that is why phonetics claims to be of equal importance with grammar and lexicology. Phonetics has two main divisions: phonology, the Study of sound patterns of languages, of how a spoken language functions as a "code", and the study of substance, that carries the code. It shows !that there is a close relationship between the language and thought. In modern linguistics this relationship is explained the terms of distinctions: substance and form. By the term "substance" we mean the material - carries of all the elements of a language and the term "form" we mean linguistic concepts. Human speech is called the "phonic substance" in which linguistic forms are manifested. The speech may be either oral or written. The term "phonetics" comes - from the Greek word "pho:n" - meaning sound, voice and "-tica" - a science. So, phonetics is a special science which studies the phonetic substance and expressions area of the language. The linguistic form and content are described by other brunches of linguistics, namely grammar (morphology and syntax) lexicology (vocabulary, the formation and the meaning of the words) and stylistics (expressive - emotional meaning).

Human speech is the result of a highly complicated series of events. The formation of the concept takes place at a linguistic level, that is in the brain of the speaker;

This stage may be called psychological. The message formed within the brain 1 s transmitted along the nervous system to the speech organs. Therefore we may say that the human brain controls the behaviour of the articulating organs which effects in producing a particular pattern of speech sounds. This second stage may be called physiology cat. The movements of the speech apparatus disturb the air stream thus producing sound waves. Consequently the third stage may be called physical or acoustic. Further, any communication requires a listener, as well as a speaker. So, the last stages are the reception of the sound waves by the listener's ,hearing physiological apparatus, the transmission of the spoken message through the nervous system to the brain and the 1 i n g u i s t i c interpretation of the information conveyed.

In accordance with their linguistic function the organs of speech may be grouped as follows:                                                                                                       -

The repertory or power mechanism furnishes the flow or the air which is the first requisite for the production of speech sounds. This mechanism is formed by the lungs, the wind pipe and the bronchi. The energy which is regulated by the power mechanism. Regulating the force of the air - wave the lungs produce variations in the intensity of speech sounds. Syllabic pulses and dynamic stress are directly related to the behavior of the muscles which activate this mechanism.

From the lungs through the wind - pipe the air - stream passes to the upper stages of the vocal tract. First of all it passes to the larynx containing the vocal cords. The function of the vocal cords consists in their role as a vibrator set in motion by the air - stream sent by the lungs. At least two actions of the vocal cords as a vibrator should be mentioned.

The opening between the vocal cords is known as the glottis.         .

The most important speech function of the vocal cords is their role in the production of voice. The effect of voice is achieved when the vocal cords are brought together and vibrate when subjected to the pressure of the air - passing from the lungs. This vibration is caused by compressed air forcing an opening of the glottis and the following reduced air - pressure permitting the vocal cords to come together.

The height of the speaking voice depends on the frequency of the vibrations. The more frequently the vocal cords vibrate the higher the pitch is.

From the larynx the stream passes to the pharynx, the mouth and the nasal cavities. The shapes of these Cavities modify the note produced in the larynx thus giving rise to particular speech sounds. ..

The following four main types of phonetics may be distinguished:

1. General Phonetics which studies the human sound producing possibilities, the functioning of his speech mechanism and the ways they are used in all languages to pronounce speech sounds, syllables, stress and intonation. It is apart of General Linguistics.

2. Descriptive Phonetics studies the phonetic system of a certain language. For example: English Phonetics, Uzbek Phonetics etc.

3. Historical or Diachronical Phonetics which studies the changes a sound undergoes in the development of a language and languages.

4. Comparative - Typological Phonetics. It studies the phonetic features         of two or more languages of different system such as English, Russian, Uzbek etc. It is part of Comparative - Typological Linguistics.