Page 105 - Master Handbook of Acoustics

FIGURE 5-2 Sound spectrographs of human sounds other than speech. (AT&T Bell Laboratories.)

Speech

There are two quasi-independent components in the generation of speech sounds: the sound source
and the vocal system. In general, speech is a two-stage process, as pictured in Fig. 5-3A, in which the
raw sound is produced by a source and subsequently shaped in the vocal tract. To be more exact,

three different sources of sound are shaped by the vocal tract, as shown in Fig. 5-3B. First, there is
the sound we naturally think of—the sounds emitted by the vocal cords. These are formed into the
voiced sounds. They are produced by air from the lungs flowing through an open vocal tract, past the
slit between the vocal cords (the glottis), which causes the cords to vibrate. This air stream, broken
into pulses of air, produces a sound that can almost be called periodic, that is, repetitive in the sense

that one cycle follows another. The result is vowel sounds such as a, e, i, and o.