III. THE ACOUSTIC AND AUDITORY ASPECTS OF THE ENGLISH SPEECH SOUNDS

The auditory aspect of any sound is inseparable from its acoustic aspect and acoustic phonetics is closely connected with auditory phonetics and both may, therefore, be considered together.

Objectively sound is a physical phenomenon, a kind of moving energy generated by some vibrating body. Subjectively sound is our perception of the vibrations of the air next to our ear-drum. People can perceive not all vibrations of the air but only when they occur at the rate of sixteen to twenty thousand times per second.

Sounds may be periodical and non-periodical. If the vibrations of a physical body (vocal cords in our case) are rhythmical, the sound waves are periodical. The auditory impression of such periodical waves is a musical tone or a speech tone. If the wave is non-periodical, it is perceived as noise.

Sound has a number of physical properties which all exist and manifest themselves simultaneously. They can be singled out from the others only for purposes of analysis.

The first of these properties is frequency which is a number of vibrations per second. Our perception of the frequency is the pitch of the sound. The greater the frequency, the higher the pitch and vice versa. The frequency depends on certain physical properties of the vibrator, such as its mass, length and tension. The greater the mass of the vibrator, the slower its vibrations and the lower the pitch. The longer the vibrator, the slower the vibrations and the lower the frequency and the pitch. Here the difference between men and women and adults and children voices lies. Men's and adults' voices are lower than women's and children's are, because their vocal cords are thicker and longer. Tension depends on the elasticity of the vocal cords. The vocal cords of elderly people are not as elastic as the vocal cords of younger people, children especially, so their voices sound rather low. As the tension increases - the frequency increases and the pitch rises.

The second physical property of sound is intensity, changes in which are perceived as variations in the loudness of sound. The intensity of sound is produced by the amplitude of vibrations (that is by the distance to which the air particles are displaced from their position of rest by the application of some external force). Intensity is measured in decibels. The intensity and frequency of sound are closely interdependent. The same amount of energy will produce either greater amplitude with a lower frequency or a higher frequency with smaller amplitude. Therefore if you increase the frequency without increasing the amount of energy you will shorten the amplitude and therefore reduce the intensity, that is produce a less loud sound.

People are able to produce vowel sounds of various qualities or timbres. This is achieved through the action of the resonator mechanism. So the production and differentiation of vowels is based on the acoustic phenomenon that is called resonance. Sounds coming from different resonators travel different lengths (distances) or have different carrying power. The distance is proportional to the volume of the resonator and the size of its orifice.

Any sound has a certain duration or length. In other words it can exist and move only in time. The duration or length of a sound is the quantity of time during which the same vibratory motion, the same patterns of vibration are maintained. For this reason, the duration of a sound is often referred to as is quantity. The duration is measured in millisecond. We perceive the variations in duration as tempo or speed of utterance. In speech there are not definite boundaries between different speech sounds. So it’s very difficult to measure the length of separate sounds.

In addition it should be mentioned that along with various articulatory classifications of speech sounds, there exist acoustic descriptions and classifications.

The chief drawback of articulatory classifications is that they don’t describe and define all shades of typologically identical speech sounds, especially vowels. Besides, one and the same speech sound can be pronounced by different people with slightly different positions and movements of their speech organs. Acoustic classifications seem to overcome these difficulties as they are more detailed and accurate. The first acoustic classification was based on spectrographic analysis. It was worked out by Roman Jakobson, C. G. M. Fant and M. Halle.

However, acoustic classification, though more precise, are not practically applied in teaching. The acoustic features of speech sounds can not be seen directly or felt. But there are some other fields of the application of acoustic phonetics: speech synthesis, health service, security systems, etc.

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