A subfield of phonetics, acoustic phonetics deals with the acoustic properties of spoken language. Researchers in this field use technological tools to analyze spoken sounds and to break them down into their component parts. The study of these linguistic components helps practitioners of acoustic phonetics understand the production and reproduction of language.
All objects can produce sound, including guitar strings, speaker cones or even coins jingling in a pocket. These sources vibrate to produce cycles of compression and rarefaction in the air. When those cycles reach a person’s ears, if the frequencies are within the range of human hearing, they are perceived as sound. These cycles are represented as waves, and most of the sounds that humans hear are complex waveforms composed of many frequencies layered together.
Every sound source produces one dominant frequency, known as the formant, as well as a set of related frequencies called harmonics. As these frequencies pass through a medium, such as air or wood, the shape and material of the medium will amplify some frequencies while dampening others. This is the principle behind instrument design; the shape and type of wood used in the body of a guitar, for example, determine the instrument’s unique sound.
Acoustic phonetics is concerned specifically with the linguistic sounds that humans produce in spoken language. In human speech, the vocal cords are the sound source, and the mouth filters the waves they produce to create specific complex waveforms that correspond with phonetic units of speech. For example, each different vowel sound is produced by holding the mouth in a certain way to produce a specific combination of sound frequencies.
Practitioners of acoustic phonetics use spectral analysis to break down complex waveforms into individual frequencies. Spectrum diagrams are visual illustrations of the individual frequencies that combine to produce a waveform at a specific point in time. These diagrams detail the amplitudes of each component frequency in the moment being diagrammed. Spectrograms are another type of visual representation that shows changes in those frequencies over time.
The findings of acoustic phonetics are applied in various disciplines. Speech pathologists might use acoustic phonetics in the assessment and treatment of speech disorders. Acoustic phonetics also is used in the application of technologies that are concerned with the recording and reproduction of human speech, such as the telephone.