In order to research the
sounds that humans make when they talk, it is important to know what
kinds of sounds we as humans are capable of producing. In linguistics,
the basic unit of sound is called a phoneme. There are two general categories
of phonemes: vowels and consonants.
Vowels are formed by pushing
air from the lungs through the vocal tract while the vocal chords are
vibrating. The position of the tongue and lips change the shape of the
vocal tract which creates different resonant frequencies. The vowel
chart seen in Figure 2 not only corresponds to the position of
the tongue in the mouth, but it is also directly related to the first
two formant frequencies of a vowel. The back chamber in the mouth amplifies
the first formant, and the front chamber amplifies the second formant.
For example, the vowel /i/ is a high front vowel. This means that the
back chamber is large and the front chamber is small. Indeed, we find
that the first formant for /i/ is low, and the second formant is quite
high.
Figure 2
Consonants are different
from vowels because they involve an occlusion of the vocal tract. This
closure takes place at the beginning of the consonant and is then released
in some fashion. By changing the place of articulation, manner of articulation,
and voicing of the sound produced, humans can create different consonants.
Place of articulation refers to the place in our mouth or throat that
our tongue touches. In English, either the lips close together or else
the tongue makes contact with the teeth, the alveolar ridge, the palate,
or the velum (see Figure 1).
Manner of articulation refers to way in which the release happens. A
stop is produced when there is a burst of air through the vocal tract,
like when the sounds at the beginning of the words 'pat' and 'bat' are
produced. When the occlusion is semi-released, a fricative is produced,
such as 's' and 'z'. Finally, if our vocal chords are vibrating during
the production of the sound, the phoneme is said to be voiced (b and
z), whereas if the vocal chords are not vibrating, the phoneme is said
to be unvoiced (p and s). The pitch of a person's voice, or their fundamental
frequency, is determined by the frequency at which the vocal chords
vibrate during the production of voiced phonemes.