Phonetics is one of the branches of linguistics. Linguistics is an academic field of inquiry that embraces the study of language as a whole, whereas phonetics narrowly focuses on examining, describing and understanding the sounds of human speech. As a discipline, phonetics is further broken down into three different fields — articulatory, acoustic and auditory phonetics — with each one contributing its own perspective to the study of human speech sounds. Taken together, these three fields focus on how sounds are produced by the human speech organs, what their actual physical properties are and, finally, how the hearer of the sounds perceives them.
Articulatory phonetics is the oldest of the three fields and is the one in which the concepts that are fundamental to phonetic study were first defined. This field focuses on the speaker and studies how air and the different parts of the vocal tract move and interact to produce the actual sounds of speech. For example, research might be done on how the lips, teeth and air are used to produce the sound at the beginning of the word "far." In addition, this field devotes study to the classification and categorization of speech sounds, such as vowels and consonants, to be able to assess and provide therapy for different speech disorders by teaching pronunciation and how to correctly form sounds and words.
Acoustic phonetics studies the physical properties of the sound waves that transmit the sounds of speech between the mouth of the speaker, through the air and to the ears of both the hearer and the speaker. This is the newest of the three fields, and its development as a discipline was accelerated by the invention of the phonograph and the telephone. These inventions allowed the study of the acoustical properties of sound waves to be done using sophisticated instruments such as a spectrogram. Researchers into acoustical phonetics will describe sound waves transmitted in the air by using the concepts of mathematics and physics, such as frequency, amplitude and duration, to measure the waves.
Auditory phonetics focuses on the hearer of speech sounds and studies how these sounds are heard through the ear, transmitted along the neural network, then perceived in the brain. Studies in the auditory field are difficult because most of the processes related to speech perception and analysis happen in the brain, which is more difficult to observe than the vocal tract. A knowledge of auditory phonetics is essential to the study and treatment of deafness.