The production of speech sounds may also involve other methods that require special features for adequate description. For example, vowels or consonants may be long or short in duration. A vowel can be lengthened beyond its 'characteristic' length of prolonging it. A consonant is made long by maintaining the closure or obstruction for a longer period of time.
When we speak we also change the pitch of our voice. The pitch producted depends upon how fast the vocal cords vibrate; the faster they vibrate, the higer pitch. In physical or acoustic terms, pitch is reffered to as the fundamental frequency of the sound signal.
We are also able to change the loudness of the sounds and sound sequences. In many languages, some syllables or vowels are produced with a chang in pitch (usually higer), more loudly, and longer than other vowels in the word or sentence. They are referred to as stressed or accented syllables or vowels.
For example, the first syllable of digest, the noun meaning 'summation of articles' or a 'journal', is stressed, while in digest, the verb meaning 'to absorb food', the second syllable is stressed. Stress can be marked in a number of ways, such as by putting an 'accent' mark over the stressed vowel.
Features such as length, pitch, and the complex feature stress are used in various languages to distinguish the meaning of words and sentences. Such feature are often referred to as prosodic or suprasegmental features.
