Phonetics is the study of speech sounds. It is concerned with the actual nature of the sounds and their production, as opposed to phonology which operates at the level of sound systems (see also phoneme).
The object of study of phonetics are called phones. Phones are actual speech sounds as uttered by human beings.
There are two main branches of phonetics, articulatory phonetics and acoustic phonetics. There are several hundred different phones recognized by the International Phonetic Association (IPA) and transcribed in their International_Phonetic_Alphabet.
Of all the speech sounds that a human vocal tract can create, different languages vary considerably in the number of these sounds that they use. Languages can contain from 2 to 30 vowels and 5 to over 100 consonants (roughly, anyone know exact numbers?). The total number of phonemes in languages varies from as few as 11 in Rotokas (spoken in Papua New Guinea) and 12 in Hawaiian to as many as 147 in !Xu~ (spoken in southern Africa, in the vicinity of the Kalahari desert). These may range from familiar sounds like [t], [s] or [m] to very unusual ones produced in extraordinary ways (see: clicks, phonation, airstream mechanism). The English language is pretty close to average, using 13 vowels and over 30 consonants. This differs from the lay definition based on the Latin alphabet, where there are 21 consonants and 5 vowels (although sometimes y and w are included as vowels).
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