Formants and Vowels

The formants that characterize different vowels are the result of the different shapes of the vocal tract. Any body of air, such as that in the vocal tract or that in a bottle, will vibrate in a way that depends on its size and shape. If blowing across the top of an empty bottle, we can usually produce a low-pitched note. If partially filling the bottle with water so that the volume of air is smaller, we can produce a note with higher pitch. Smaller bodies of air, like smaller piano strings or smaller organ pipes, produce higher pitches. In the case of vowel sounds, the vocal tract has a complex shape so that the different bodies of air produce a number of formants[14].

The vowels, especially monophthongs, have strong stable formants. In addition, these vowels can usually be easily distinguished by the frequency values of the first two or three formants. For , the lower it is, the closer the tongue is to the roof of the mouth. The value is proportional to the frontness or backness of the highest part of the tongue during the production of the vowel. Moreover, lip rounding causes a lower than with unrounded lips. In the production of this vowel the tongue tip is quite far forward and the lips are unrounded. is also important is determining the phonemic quality of a given speech sound, and the higher formants such as and are thought to be significant in determining voice quality. it is important to remember that all voiced phonemes have formants, even if they are not as easy to recognize and classify as the monophthong vowel formants.

  
図 2.3: Speech waveform, pitch, power and LPC spectrum plots