2.1.3 Vowels

Vowels are sounds in which there is no obstruction to the flow of air as it passes through the vocal tract. They are distinguished from each other by the way the vocal tract is modified by lips and tongue which also modifies the sound produced. (Meyer 2002: 101).

The waveform of vowels is periodic. The energy is concentrated in the lower half of the spectrum and the formants are salient due to the resonance of the vocal tract (cf. Harrington 1997: 83). The fundamental frequency of a vowel is what we perceive as the pitch of the voice.

The other frequencies which sound along are the so called harmonics or formants. They “(...) represent the non-fundamental frequencies of the signal, which are produced by the sound-specific form of the vocal tract, and which allow the hearer to distinguish different sound qualities.” (Meyer 2002: 117).

The different qualities of sounds enable us to recognize for example the sound of a particular instrument or a particular human voice.

The formants are clearly visible in a spectrographic display and they occur on average at intervals of c/2L, where c is the speed of sound and L the length of the vocal tract (Fant, 1973) - that is, at about 1,000 Hz intervals for an adult male vocal tract of length 17.5 cm (and with the speed of sound at 35,000 cm/s). (Harrigton 1997: 83).

The first (F1) and second (F2) formants give us information about the movements within the oral cavity. If the first formant (F1) is maximally high, this indicates that the main obstruction is located just above the larynx and that the oral cavity is wide open, while a maximally high F2 is likely to advert to a tongue constriction in the palatal region (cf. Harrington 1997: 84).

It has also been shown that by plotting the F1 and F2 frequencies a speaker-specific vowel chart can be created. This is due to the correlation between phonetic height and the F1 value and phonetic backness and the F2 value.

Most of the time, the third formant can be neglected for charting vowels since it can be predicted by looking at the first two formant frequencies.

The frequency of the third formant is very much affected by the position of the lips. This makes it more important in some languages. It so happens that neither General American English nor BBC English has vowels with the same tongue positions but different lip positions (Ladefoged 2001: 48).

In other languages like French or German the F3 value is more important than in English where it is only necessary in the /ɜː/ vowel, for example in bird.

Created with the Personal Edition of HelpNDoc: Produce electronic books easily