PHONETICS. In its broadest sense, a study of the whole range of sounds, articulate, musical, and otherwise. it is, however, usually confined to the articulate sounds of human speech. Even in this restricted sense, it is still broad enough to include the subject of the purely acoustic or mechanical side and the anthropological or phil ological side. It may discuss simply the vibra tions that cause any particular sensation on the human ear, or it include an investigation of the manner and causes of the change of one articulate sound in one language at one time, into another sound in another language or at another epoch. In the first case it should con sider the mechanism and methods by which the sounds are produced, and also the way in which they are made effective in the ear, and impress the brain.
The question of the variations of articulate sounds and of the symbols which from time to time may be used to represent them belongs to the sphere of comparative philology (q.v.), and is not, therefore, discussed in this article.
Confining the attention to the physics of pho netics. the subject naturally falls under three beads, or questions: What is tone quality, or the mechanical difference between two sounds? How are sounds produced in the human voice? and How are they perceived in the ear? The divisions may best be treated'in the order given.
One sound differs from another in three factors, pitch, intensity, and quality. (See ACOCSTICS.) The pitch and intensity, or loudness, are of but little importance in this connection. The con trolling factor is the quality. In articulation the sounds are divided into two broad classes: the vowel sounds, or those which are maintained in more or less uniform quality for an appreciable length of time; and the consonants. or those sounds which are more essentially a peculiar stopping or starting of a vowel sound, and which are apt to form the transition front one vowel to another, by some one of an infinite variety of ways.
Taking np the discussion of the vowel sounds first as being the simpler case. it is evident that these sounds, which last with a uniform char acter for an appreciable fraction of a second, or at least may be so prolonged, must depend for their distinguishing peculiarities upon the same factors as any other :sound. As the pitch of a sound depends upon the length of the wave, and the intensity upon the height of the wave, so does the quality of the sound depend upon the shape of the wave. It has been demonstrated that any wave motion, no matter how complex, may be considered as made up of a series of simple waves of differing lengths and heights. Therefore, any quality of sound. no matter how complex, is made up of simple components, dif fering in pitch and intensity. By a simple sound is meant one in which the vibrating particles move in a simple harmonic motion, similar. for example, to that executed by a clock pendulum. When a violinist plays a particular note, it dif fers from the same note on the organ or the piano or the wind instrument, only in the relative number, intensity, and pitch of the 'partials' 'overtones' which accompany the fundamental. or
'pitch-tone.' In a manner entirely analogous the maintained sounds of the human voice differ one from another. when the same fundamental tone is being produced, only in the relative number, pitch, and intensity of the accompanying partials. It is believed by sonic that the 'phase-rdation' of the components also affects the quality of the sound, but this is still an open tainly does not affect the case of articulation.
The question, then, is to determine just what are the particular combinations of elements which form the various vowel sounds. In the first place, it has been shown conclusively that the same relative components will not produce the same vowel sounds on different pitches. For ex ample, a certain combination, bearing a definite relation to a fundamental of 25(1 vibrations per second, will produce a certain vowel quality. but if the rates of all these components are raised liv the same interval of a fifth, the vowel quality will he quite different. in other words. that com bination whieh is recognized as giving a per fectly satisfactory a, as in father, on a pitch of middle c, is entirely different from that which is similarly recognized on a pitell an octave higher.
There are two conceptions at present as to what constitutes the essential characteristic of a particular vowel sound. Some hold that each vowel sound always contains in its complex a eertain characteristic tone component of definite pitch. and that the presence of this element makes that vowel. For example. a, as in father. has its essential vowel tone, and cc. as in Wet woO Id have a different tone. This theory holds that the pitch of the characteristic elements is constant. irrespective of the pitch of the fundamental. or main time. Others believe that there is no dif ference in the question of tone quality in vowels from the same question as applied to any tone. Under this conception there would be no one es sential component. but all would be essential and the total would be characteristic. This would mean that the difference between o and a pro nounced on treble c is of exactly the same char acter as that between the two sounds when that note is played upon a flute and upon a violin. 111 other words, vowel quality is no different from tone quality.
The actual solution of this question is enor mously complieated by the fact that habit allows the greatest possible variation in what may still be called a particular vowel. For example. the a in different may differ more radi cally than the a and o in the same individual.
Helmholtz seems to hold to both theories. and gives the following as the pitches of the char acteristic tones of the vowels: U = 175; 0 =