Speech sounds can be classified and described in articulatory, acoustic and auditory terms. On the basis of these terms the two broad categories in which the speech sounds in any language can be classified are vowels and consonants. Consonants are best described in articulatory terms because there is some type of closure or narrowing of the air passage to the extent that there is audible friction during the production of that sound. But in case of the production of vowels as there is no closure and no narrowing of the air passage to the extent that it may produce audible friction both articulatory and auditory terms are used to describe and classify them. In Phonetic terms vowels are speech sounds in the production of which there is no obstruction or closure and no narrowing of a degree that would cause audible friction in the pharynx and the mouth.
Vowels are essentially a tone issuing from the glotis with the vocal chords vibrating. Classification and description of vowels becomes difficult due to the fact that the distinction of one vowel from another arises because of the modification in the shape and size of the resonating chambers, that is the pharyngeal cavity, nasal cavity and the mouth. Soft Palate, the lips and the tongue are responsible for this modification. Thus, just as any description of consonant sounds should reveal the position of vocal cords, place of articulation and manner of articulation, similarly any description of vowel sounds describe:
1. the position of the soft palate – raised (oral) or lowered (nasalized).
2. The shape of the lips –1
i. Unrounded – spread, neutral, open
ii. Rounded – open and close
3. The shape of the tongue
i. which part of the tongue is raised – front, central and back. ii. How high is the part of the tongue is raised – close, half close, half open and open. The position of the soft palate is judged by auditory perception. The shape of the lips can be observed by the eye and therefore described in articulatory terms. But the shape and position of the tongue changes so minutely that it is very difficult to feel these changes. So most of the positions of the tongue are judged by auditory perception only.
Thus it is clear that a finer and more independent system of description is needed on the auditory and articulatory levels. The most satisfactory scheme was devised by Daniel Jones and is known as the Cardinal Vowel system. The basis of the system is physiological. The vowel sounds were produced with the tongue in certain easily felt position. The front of the tongue was raised as close as possible to the palate without causing friction and the sound produced was that of the cardinal vowel [ i ]. Starting from the [ i ] , the front of the tongue was lowered gradually, the lips remained in the spread or the open position and the soft palate was in raised position. The lowering of the tongue was halted at three points at which the vowel qualities seemed to be equi-distant from the auditory point of view.
These three tongue positions were x-rayed and it was found that these three points were almost equi-distant from a spatial point of view. The symbols assigned to these three positions were [ e, Ɛ , a ]. The same procedure was applied to the vowels which are produced by raising the back of the tongue. The sound produced when the whole of the tongue was as low as possible with a slight raising at the back of the tongue was termed as the cardinal vowel [ ]. The lips were changed progressively from a wide open shape to closely rounded one and the soft palate remained in the raised position. Once again three auditorily and spatially equi-distant points were found. These points were were assigned the symbols – [ , o, u ]. Thus a scale of eight primary cardinal vowels was set up. They were denoted by the following numbers and symbols: 1, [ i ] ; 2, [e] ; 3, [Ɛ] ; 4, [a] ; 5, [ ] ; 6, [ ] ; 7, [o] ; 8, [u]. The usefulness of Cardinal Vowels
Such a scale is useful because:
a. these cardinal vowel sounds are unrelated to particular values in languages, though they may occur in various languages, and b. the set of cardinal vowels is recorded so that reference may always be made to a standard. A vowel sound may be described as being similar to a particular cardinal vowel. These cardinal vowels can be represented diagrammatically. A vowel diagram is obtained by plotting the highest point of tongue raising for each of the primary cardinal vowels and joining the points together. The internal triangle, corresponding to the region of central vowel sounds, is made by dividing the top line into three approximately equal sections and drawing lines parallel to the two sides so that they meet near the base of the figure.
C [ i ] C [u]
C [ e ] C [ o ]
C [ Ɛ ]C [ ]
C [ a ]C [ ]
Monophthongs and Diphthongs
There are twenty vowel sounds in RP. These vowel sounds can be divided into two types – monophthongs and diphthongs – on the basis of whether the quality the vowel sound changes during their production or not. Vowel sounds, during the production of which there is no considerable and voluntary change in the quality of the sound are called monophthongs or pure vowels. For example, the vowel sound / I / in ‘pin’. They are represented by thick dots in the vowel diagram. There are 12 monophthongs in RP. Similarly, vowel sound, during the production of which there is considerable and voluntary change in the quality of the sound is called diphthongs or gliding vowel. For example the / aI / sound in ‘pine’. (Explain). They are represented by arrows in the vowel diagram indicating the starting point and the direction in which the quality change, corresponding to the movement of the tongue, is made. There are 8 diphthongs in RP.
It should be noted that a diphthong is not the same thing as a sequence of two monophthongs. The diphthong occupies one syllable while a sequence of two monophthongs is spread over two syllables. Example: soil, sawing. During the description of a diphthong we have to describe the lip position and the tongue position at the starting point and the lip position and the tongue position after it has glided in a particular direction.
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