x or tense in the direction of their
length. The last class of these movements allows the cords to vibrate at
different "lengths" or degrees of tenseness and is responsible for the
variations in pitch which are present not only in song but in the more
elusive modulations of ordinary speech. The two other types of glottal
action determine the nature of the voice, "voice" being a convenient
term for breath as utilized in speech. If the cords are well apart,
allowing the breath to escape in unmodified form, we have the condition
technically known as "voicelessness." All sounds produced under these
circumstances are "voiceless" sounds. Such are the simple, unmodified
breath as it passes into the mouth, which is, at least approximately,
the same as the sound that we write _h_, also a large number of special
articulations in the mouth chamber, like _p_ and _s_. On the other hand,
the glottal cords may be brought tight together, without vibrating. When
this happens, the current of breath is checked for the time being. The
slight choke or "arrested cough" that is thus made audible is not
recognized in English as a definite sound but occurs nevertheless not
infrequently.[14] This momentary check, technically known as a "glottal
stop," is an integral element of speech in many languages, as Danish,
Lettish, certain Chinese dialects, and nearly all American Indian
languages. Between the two extremes of voicelessness, that of
completely open breath and that of checked breath, lies the position of
true voice. In this position the cords are close together, but not so
tightly as to prevent the air from streaming through; the cords are set
vibrating and a musical tone of varying pitch results. A tone so
produced is known as a "voiced sound." It may have an indefinite number
of qualities according to the precise position of the upper organs of
speech. Our vowels, nasals (such as _m_ and _n_), and such sounds as
_b_, _z_, and _l_ are all voiced sounds. The most convenient test of a
voiced sound is the possibility of pronouncing it on any given pitch, in
other words, of singing on it.[15] The voiced sounds are the most
clearly audible elements of speech. As such they are the carriers of
practically all significant differences in stress, pitch, and
syllabification. The voiceless sounds are articulated noises that break
up the stream of voice with fleeting moments of silence. Acoustically
intermediate between the freely unvoiced and the voiced