The general study of the characteristics of speech sounds is called phonetics. Our main interest will be in articulatory phonetics, which is the study of how speech sounds are made, or ‘articulated’. Other areas of study are acoustic phonetics, which deals with the physical properties of speech as sound waves in the air, and auditory phonetics (or perceptual phonetics) which deals with the perception, via the ear, of speech sounds.
"Phonetics studys the signifier of the speech" (Saussure).

It is important doesn´t confuse phonetics with phonology, or phoneme with allophone or sound, or letter. A letter is the representation as phonema in writting. Phonemes, and everything that relates to the phonological level, are set between / /, while as regards phonetic level (allophones or sounds) is reproduced in [].