Phonetics (pronounced /fəˈnɛtɪks/) is the branch of linguistics that studies the sounds of human speech, or—in the case of sign languages—the equivalent aspects of sign. It is concerned with the physical properties of speech sounds or signs (phones): their physiological production, acoustic properties, auditory perception, and neurophysiological status. Phonology, on the other hand, is concerned with the abstract, grammatical characterization of systems of sounds or signs.
In the case of oral languages, phonetics has three basic areas of study:
Phonetics was studied by 4th century BCE, and possibly as early as the 6th century BCE, in the Indian subcontinent, with Pāṇini's account of the place and manner of articulation of consonants in his treatise on Sanskrit. The major Indic alphabets today order their consonants according to Pāṇini's classification.
Modern phonetics begins with attempts—such as those of Joshua Steele (in Prosodia Rationalis, 1779) and Alexander Melville Bell (in Visible Speech, 1867)—to introduce systems of precise notation for speech sounds.
The study of phonetics grew quickly in the late 19th century partly due to the invention of the phonograph, which allowed the speech signal to be recorded. Phoneticians were able to replay the speech signal several times and apply acoustic filters to the signal. By doing so, they were able to more carefully deduce the acoustic nature of the speech signal.
Using an Edison phonograph, Ludimar Hermann investigated the spectral properties of vowels and consonants. It was in these papers that the term formant was first introduced. Hermann also played vowel recordings made with the Edison phonograph at different speeds in order to test Willis', and Wheatstone's theories of vowel production.
In contrast to phonetics, phonology is the study of how sounds and gestures pattern in and across languages, relating such concerns with other levels and aspects of language. Phonetics deals with the articulatory and acoustic properties of speech sounds, how they are produced, and how they are perceived. As part of this investigation, phoneticians may concern themselves with the physical properties of meaningful sound contrasts or the social meaning encoded in the speech signal (socio-phonetics) (e.g. gender, sexuality, ethnicity, etc.). However, a substantial portion of research in phonetics is not concerned with the meaningful elements in the speech signal.
While it is widely agreed that phonology is grounded in phonetics, phonology is a distinct branch of linguistics, concerned with sounds and gestures as abstract units (e.g., distinctive features, phonemes, morae, syllables, etc.) and their conditioned variation (via, e.g., allophonic rules, constraints, or derivational rules). Phonology has been argued to relate to phonetics via the set of distinctive features, which map the abstract representations of speech units to articulatory gestures, acoustic signals or perceptual representations.
Phonetics as a research discipline has three main branches:
Phonetic transcription is a system for transcribing sounds that occur in a language, whether oral or sign. The most widely known system of phonetic transcription, the International Phonetic Alphabet (IPA), provides a standardized set of symbols for oral phones. The standardized nature of the IPA enables its users to transcribe accurately and consistently the phones of different languages, dialects, and idiolects. The IPA is a useful tool not only for the study of phonetics, but also for language teaching, professional acting, and speech pathology.
Applications of phonetics include:
Studying phonetics involves not only learning theoretical material but also undergoing training in the production and perception of speech sounds. The latter is often known as ear-training. Students must learn control of articulatory variables and develop their ability to recognize fine differences between different vowels and consonants. As part of the training, they must become expert in using phonetic symbols, usually those of the International Phonetic Alphabet.