Vowel


A vowel is a speech sound pronounced without any in the vocal tract. Vowels are one of the two principal classes of speech sounds, the other being the consonant. Vowels vary in quality, loudness, and length. They are usually voiced and are closely involved in prosodic variation such as tone, intonation and stress. The nucleus, or "center", of a syllable typically consists of a vowel sound.
The word vowel comes from the Latin word vocalis, meaning "vocal".
In English, the word vowel is commonly used to refer both to vowel sounds and to the written symbols that represent them:,,,,, and sometimes, and.

Definition

There are two complementary definitions of vowel, one phonetic and the other phonological.
  • In the phonetic definition, a vowel is a sound, such as the English "ah" or "oh", produced with an open vocal tract; it is median, oral, frictionless and continuant. There is no significant build-up of air pressure at any point above the glottis. This contrasts with consonants, such as the English "sh", which have a constriction or closure at some point along the vocal tract.
  • In the phonological definition, a vowel is defined as syllabic, the sound that forms the peak of a syllable. A phonetically equivalent but non-syllabic sound is a semivowel. In oral languages, phonetic vowels normally form the peak of many or all syllables, whereas consonants form the onset and coda. Some languages allow other sounds to form the nucleus of a syllable, such as the syllabic l in the English word table or the syllabic r in the Serbo-Croatian word vrt "garden".
The phonetic definition of "vowel" does not always match the phonological definition. The approximants and illustrate this: both are without much of a constriction in the vocal tract, but they occur at the onset of syllables which suggests that phonologically they are consonants. A similar debate arises over whether a word like bird in a rhotic dialect has an r-colored vowel or a syllabic consonant. The American linguist Kenneth Pike suggested the terms "vocoid" for a phonetic vowel and "vowel" for a phonological vowel, so using this terminology, and are classified as vocoids but not vowels. However, Maddieson and Emmory demonstrated from a range of languages that semivowels are produced with a narrower constriction of the vocal tract than vowels, and so may be considered consonants on that basis. Nonetheless, the phonetic and phonemic definitions would still conflict for the syllabic /l/ in table or the syllabic nasals in button and rhythm.

Articulation

The traditional view of vowel production, reflected for example in the terminology and presentation of the International Phonetic Alphabet, is one of articulatory features that determine a vowel's quality as distinguishing it from other vowels. Daniel Jones developed the cardinal vowel system to describe vowels in terms of the features of tongue height, tongue backness and roundedness. These three parameters are indicated in the schematic quadrilateral IPA vowel diagram on the right. There are additional features of vowel quality, such as the velum position, type of vocal fold vibration, and tongue root position.
This conception of vowel articulation has been known to be inaccurate since 1928. Peter Ladefoged has said that "early phoneticians... thought they were describing the highest point of the tongue, but they were not. They were actually describing formant frequencies." The IPA Handbook concedes that "the vowel quadrilateral must be regarded as an abstraction and not a direct mapping of tongue position."
Nonetheless, the concept that vowel qualities are determined primarily by tongue position and lip rounding continues to be used in pedagogy, as it provides an intuitive explanation of how vowels are distinguished.

Height

Theoretically, vowel height refers to the vertical position of either the tongue or the jaw relative to either the roof of the mouth or the aperture of the jaw. In practice, however, it refers to the first formant, abbreviated F1, which is associated with the height of the tongue. There are two terms commonly applied to refer to two degrees of vowel height: in close vowels, also known as high vowels, such as and, the first formant is consistent with the tongue being positioned close to the palate, high in the mouth, whereas in open vowels, also known as low vowels, such as, F1 is consistent with the jaw being open and the tongue being positioned low in the mouth. Height is defined by the inverse of the F1 value: the higher the frequency of the first formant, the lower the vowel. In John Esling's usage, where fronted vowels are distinguished in height by the position of the jaw rather than the tongue, only the terms 'open' and 'close' are used, as 'high' and 'low' refer to the position of the tongue.
The International Phonetic Alphabet has letters for six degrees of vowel height for full vowels, but it is extremely unusual for a language to distinguish this many degrees without other attributes. The IPA letters distinguish :
The letters are defined as close-mid but are commonly used for true mid vowels. If more precision is required, true mid vowels may be written with a lowering or raising diacritic: or.
The Kensiu language, spoken in Malaysia and Thailand, is highly unusual in contrasting true mid vowels with both close-mid and open-mid vowels, without any additional parameters such as length, roundness or ATR. The front vowels,, along with open, make a six-way height distinction; this holds even for the nasal vowels. A few varieties of German have been reported to have five contrastive vowel heights that are independent of length or other parameters. For example, the Bavarian dialect of Amstetten has thirteen long vowels, which have been analyzed as four vowel heights each among the front unrounded, front rounded, and back rounded vowels, along with an open vowel for a fifth height:. Apart from the aforementioned Kensiu language, no other language is known to contrast more than four degrees of vowel height.
The parameter of vowel height appears to be the primary cross-linguistic feature of vowels in that all spoken languages that have been researched till now use height as a contrastive feature. No other parameter, even backness or rounding, is used in all languages. Some languages have vertical vowel systems in which at least at a phonemic level, only height is used to distinguish vowels.

Backness

Vowel backness is named for the position of the tongue during the articulation of a vowel relative to the back of the mouth. As with vowel height, however, it is defined by a formant of the voice, in this case the second, F2, not by the position of the tongue. In front vowels, such as, the frequency of F2 is relatively high, which generally corresponds to a position of the tongue forward in the mouth, whereas in back vowels, such as, F2 is low, consistent with the tongue being positioned towards the back of the mouth.
The International Phonetic Alphabet defines five degrees of vowel backness :
To them may be added front-central and back-central, corresponding to the vertical lines separating central from front and back vowel spaces in several IPA diagrams. However, front-central and back-central may also be used as terms synonymous with near-front and near-back. No language is known to contrast more than three degrees of backness nor is there a language that contrasts front with near-front vowels nor back with near-back ones.
Although some English dialects have vowels at five degrees of backness, there is no known language that distinguishes five degrees of backness without additional differences in height or rounding.

Roundedness

is named after the rounding of the lips in some vowels. Because lip rounding is easily visible, vowels may be commonly identified as rounded based on the articulation of the lips. Acoustically, rounded vowels are identified chiefly by a decrease in F2, although F1 is also slightly decreased.
In most languages, roundedness is a reinforcing feature of mid to high back vowels rather than a distinctive feature. Usually, the higher a back vowel, the more intense is the rounding. However, in some languages, roundedness is independent from backness, such as French and German, most Uralic languages, Turkic languages, and Vietnamese with back unrounded vowels.
Nonetheless, even in those languages there is usually some phonetic correlation between rounding and backness: front rounded vowels tend to be more front-central than front, and back unrounded vowels tend to be more back-central than back. Thus, the placement of unrounded vowels to the left of rounded vowels on the IPA vowel chart is reflective of their position in formant space.
Different kinds of labialization are possible. In mid to high rounded back vowels the lips are generally protruded outward, a phenomenon known as endolabial rounding because the insides of the lips are visible, whereas in mid to high rounded front vowels the lips are generally "compressed" with the margins of the lips pulled in and drawn towards each other, a phenomenon known as exolabial rounding. However, not all languages follow that pattern. Japanese, for example, is an exolabial back vowel, and sounds quite different from an English endolabial. Swedish and Norwegian are the only two known languages in which the feature is contrastive; they have both exo- and endo-labial close front vowels and close central vowels, respectively. In many phonetic treatments, both are considered types of rounding, but some phoneticians do not believe that these are subsets of a single phenomenon and posit instead three independent features of rounded, compressed, and unrounded. The lip position of unrounded vowels may also be classified separately as spread and neutral. Others distinguish compressed rounded vowels, in which the corners of the mouth are drawn together, from compressed unrounded vowels, in which the lips are compressed but the corners remain apart as in spread vowels.