Speaker-specific features of simple vowels in Persian based on the source-filter theory

Based on source-filter theory, the present research attempts to investigate between- and within-speaker variability in simple vowels of Persian using experimental phonetics tools. This research aims to discover which of the simple vowels of Persian represent more speaker-specific information and which acoustic parameters can better distinguish Persian speakers. To test between- and within-speaker variability, two types of acoustic parameters, one related to the larynx, i.e. fundamental frequency, and the other related to the vocal tract, i.e. formant frequencies, were selected. Fundamental frequency as well as formant values were extracted from the steady state point of the vowels uttered by twelve Persian-speaking male speakers. Speech data were recorded non-contemporaneously in laboratory environment on two different occasions separated by one to two weeks, thereby allowing for analyzing occasion-to occasion withinspeaker variability. Speech tokens were acoustically measured with PRAAT version 5.2.34 and statistical analyses were carried out with SPSS version 21 and R version 3.3.3. Results of the study indicated that the low front vowel /a/ and the third formant frequency convey more speaker-specific information compared to the other vowels and formant frequencies. In addition, discriminatory power of fundamental frequency was reported to be stronger than formant frequencies. The results also revealed that fundamental frequency is correlated with the first formant frequency which is subsequently indicative of interdependence between the source and filter sections.