Variability of Vowels of Different Prominence in Various Phrasal Positions

The position of vowels in acoustic space is described using the values of the F1 and F2 formants. The approach is determined by the need to perceptually distinguish neighboring vowels. The area occupied by a specific vowel is described as a combination of microfields with each microfield formed by a set of allophone positions of the vowel in question. The results obtained demonstrate that the variability of the allophone position in the acoustic field can be determined by a number of factors, such as the degree of prominence and vowel position in the phrase. With this aim vowel positioning in the acoustic space in words with neutral and emphatic stress was studied. The speech material for analysis comprised the word 'Stas' embedded in the carrier phrase 'Stas ne byl tihoney' ('Stas was not quiet') with the target word occupying initial, medial and final positions in the phrase; in each position the word was pronounced with neutral and emphatic stress. F1 and F2 values of the sound [a] in the word 'Stas' were extracted with the FFT method using the Praat software. The Student paired t-test was employed to note the significance of difference between the first and second formant frequencies of neutrally and emphatically stressed vowels. The analysis revealed that the vowels uttered with emphatic stress are characterized by an expansion of their acoustic vowel space by moving off the vowel space center. The displacement occurs either through an increase of F1, a decrease of F2, or both. A general trend was observed in the impact of phrasal position on vowel formant frequencies. Though the vowels under neutral stress seemed to display greater response to the phrasal position factor compared to the emphatically stressed ones, noticeable regularities could not be established due to a high intradialectal variability of speakers.