Steady-State and Transient Aspects of Vowel Production
Don Lewis · The Journal of the Acoustical Society of America · 1936
At first, to clarify concepts and to facilitate later presentation of experimental data, the steady-state (or harmonic) theory of vowel production is differentiated from the transient (or inharmonic) theory, and each is given definite formulation. It is shown that the two theories are not, as is sometimes supposed, merely two ways of viewing the same phenomenon, but are quite different in their physiological and acoustical implications. Recent experimental data are then summarized. These data, taken from the writer's work on vocal resonance and from the reported work on vowels of Trendelenburg, Wolf, Stanley and Sette, and others, indicate that vowel production is primarily a steady-state process. In other words, the data show beyond much doubt (1) that the vocal cords give rise to a cord-tone which consists of a fundamental component and a large number of its overtones; (2) that the vocal cavities, on which the cord-tone acts as a force, constitute a number of singly-resonant systems and thus serve to modify the spectrum of the energy flowing from the cords; and (3) that vowel sounds, as radiated from the mouth, are composed mainly of a harmonic series of simple motions, each of which has a determinable magnitude. The limitations of this somewhat idealized picture are set forth, with stress on the transient aspects of the process.