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.