Phonetics is the systematic study of speech and the sounds of language. Traditionally phoneticians rely on careful listening and observation in order to describe speech sounds. In doing this, a phonetician refers to a classificatory framework for speech sounds which is based on how they are made and on aspects of the auditory impression they make. The best known such framework is that of the International Phonetic Association. Much of our knowledge of the sounds of the world’s languages comes from this kind of description, which is still an important aspect of phonetics today.
Since at least the nineteenth century, however, many techniques have been applied to speech which allow it to be measured objectively. Analysis of the acoustic speech waveform, laboriously by hand in the nineteenth century, then more rapidly by electrical and electronic machines, and in the last thirty years most conveniently by digital computers, has been central. Many techniques have been applied to study what the speaker is doing to produce speech, for instances x-rays to “see inside” the mouth and throat, masks and tubes to measure air flow and pressure, and artificial palates to record tongue contact with the roof of the mouth in different sounds.
Many experiments have also been done to discover which parts of the speech signal are most important in helping the hearer to distinguish speech sounds. A great boost to such work came around the middle of the twentieth century, when the development of flexible speech synthesis allowed researchers to manipulate different acoustic aspects of the signal to test which ones are important.
The knowledge phoneticians have accumulated from this range of approaches means that we have a much better scientific understanding now than ever before of how speech works. However, the more we learn, the more we appreciate how complex speech is; whether in terms of how skilfully we control our tongue and other speech organs, or the subtlety of sound effects which languages and dialects employ, or the multiplicity of cues which our perception can make use of in decoding the speech signal. Each answer in phonetic research raises new questions!
Phonetics is often defined with respect to phonology. Both disciplines are concerned with the sound medium of language, and it is not useful to draw a hard and fast line between them. The centre of gravity of the two fields is, however, different. In general, phonology is concerned with the pattering of sounds in a language (and in language in general), and is thus comparable to areas of linguistics such as syntax and morphology which deal with structural elements of language at other levels. Phonetics is more centred on the way those structural elements are “realised” in the world, through movements of the speech organs which create the acoustic signal. Phonetics therefore has important links not only to linguistics but to natural sciences such as physics and anatomy.
Phonetics has always had applications. Traditionally it has been important for language teaching, and for speech and language therapy. Nowadays it contributes to speech technology, and increasingly to forensic science (in cases, for instance, where speaker identification is at issue).
If you are interested in phonetics, you may find the list of where BAAP members are active in the British Isles useful.