The science of speech sounds is called phonetics. It aims to provide the set of features, or properties, that can describe all sounds in humman language.
When we speak, the physical sounds we produce are continuous stretches of sound, which are the physical representation of strings of discrete linguistic segments. Knowledge of a language permits one to segment the continuous sound into linguistic units words, morphemes, and sounds.
The discrepancy between spelling and sounds in English and other languages motivated the development of phonetic alphabets in which one letter corresponds to one sound. The major phonetic alphabet in use is that of the International Phonetic Association (IPA), which includes modified Roman letters and diacritics by means of which the sounds of all human languages can be represented. To distinguish between the orthography (or spelling) of words and their pronunciation, phonetic transcriptions may be put between square brackets, as [fənetɪk] for phonetic.
All English speech sounds are produced by the movement of lung air through the vocal tract through the glottis or vocal cords, up the pharynx, through the oral cavity and out through the mouth and sometimes the nose. All human speech sounds fall into classes according to their phonetic properties or features; that is, according to how they are produced.
All speech sounds are either consonants or vowels, and all consonants are either obstruents or sonorants. Consonants are distinguished according to where they are articulated in the vocal tract theit place of articulation, including bilabial, labiodental, alveolar, palatal, velar, uvular, and glottal.
Speech sounds are also classified according to their manner of articulation. They may be voiced or voiceless, oral or nasal; they may be stops, fricatives, lateral, glides, or vowels. During the production of voiced sounds the vocal cords or glottis are together and vibrating whereas in voiceless sounds the glottis is open and non-vibrating. Voiceless sounds may be also aspirated or unaspirated. In the production of aspirated sounds the vocal cords remain apart for a brief time after the stop closure is released, thus producing a puff of air at the time of the release. Some classes of sounds combine to form the larger classes such as labials, coronals, anteriors, and sibiliants.
Vowels from the nucleus of syllables. They differ according to length: long or short; and the position of the tongue: high, mid, or low tongue; front or back of the tongue. Vowels may also be stressed (longer, higer in pitch, and louder) or unstressed.
In sign languages, instead of phonetic features there are three classes of primes hand configuration, the motion of the hand(s) toward or away from the body, and the place of articulation, or the focus of the sign's movements.
In many languages the pitch of the vowel or syllable linguistically significant: for example, two words may contrast in meaning if one is produced with a higer pitch and another with lower pitch. Such languages are called tone languages as opposed to intonation languages, in which pitch is never used to contrast words. In intonation languages, however, the rise and fall of pitch may contrast meaning of sentences. In English the statement Mary is a teacher will end with a fall in pitch, bur in the question Mary is a techer ? the pitch will rise.
Length, pitch, and loudness are prosodic or suprasegmental features. Diacritics to specify such properties as nasalisation, length, voicelessness, syllabicity, stress, tone, and rounding may be combined with the phonetic symbols for more detailed phonetic transcriptions.
By mean of these phonetic features all speech sounds of all languages can be described.
