Investigation of the Formant Structure of Persian Vowels in the Persian - Azari Bilingual Adults

Vowels are the center of syllables while formant structures are one of the most important acoustic characteristics of speech sounds that help in their articulatory and perceptual aspects. Formants represent the shape and size of the vocal tract. There exist trivial differences between the vocal tracts of different people due to which the formant structures of a vowel in one person are different from another person. Towards the end of the 20th century, advances in acoustic science and production of digital tools introduced voice acoustical characteristics analysis as another parameter of sound analysis. These voice acoustical characteristics analyses lead to better assessment of the voices. Effective treatment of speech disorders depends on accurate diagnosis by the speech-language pathologist. The relationship between the first three formants is the main component of perceptual categorization by the listener. Therefore, the aim of the current study is to determine and compare Persian vowel frequency of first, second and third formants in bilingual adults.
A cross-sectional study was performed on 50 participants (25 males and 25 females) aged 18 to 24 years. Bilingual students from Tabriz University of Medical Sciences were selected by an easy and non randomized sampling method, where the average of the first, second and the third formant frequencies for each of the six Persian vowels were taken into consideration. Data collection involved a demographic questionnaire (age, gender, bilingualism, and diseases related to the speech-breathing mechanism), the consent form, a computer equipped with PRATT Software and one sound recorder set. The data were analyzed using SPSS V. 18 software. When the data were normally distributed, independent t-test was used; otherwise, Mann-Whitney test was used.
This study showed that the maximum and minimum values of F1 in the males and females are /æ/ and /i/ vowels. The maximum and minimum values of F2 are /i/ and /o/ vowels in both the sexes, whereas, the maximum and minimum values of F3 are /i/ and /æ/ vowels in males and /i/ and /a/ vowels in the females.
According to the results of this study, / æ/ and /i/ vowels in both the sexes are the most open and closest. /i/ and /o/ vowels in both the sexes are the most front and most back vowels. The most spread vowel in males and females is /i/ but the roundest vowel is /æ/ in the males and /a/ vowel in females.