Average Formant Trajectories

Purpose The use and study of formant frequencies for the description of vowels is commonplace in acoustic phonetics and in attempts to understand results of speech perception studies. Numerous studies have shown that listeners are better able to distinguish vowels when the acoustic parameters are based on spectral information extracted at multiple time points during the duration of the vowel, rather than at a single point in time. The purpose of this study was to validate an automated method for extracting formant trajectories, using information across the time course of production, and subsequently characterize the formant trajectories of vowels using a large, diverse corpus of speech samples. Method Using software tools, we automatically extract the 1st 2 formant frequencies (F1/F2) at 10 equally spaced points over a vowel's duration. Then, we compute the average trajectory for each vowel token. The 1,600 vowel observations in the Hillenbrand database and the more than 50,000 vowel observations in the TIMIT database are analyzed. Results First, we validate the automated method by comparing against the manually obtained values in the Hillenbrand database. Analyses reveal a strong correlation between the automated and manual formant estimates. Then, we use the automated method on the 630 speakers in the TIMIT database to compute average formant trajectories. We noted that phonemes that have close F1 and F2 values at the temporal midpoint often exhibit formant trajectories progressing in different directions, hence highlighting the importance of formant trajectory progression. Conclusions The results of this study support the importance of formant trajectories over single-point measurements for the successful discrimination of vowels. Furthermore, this study provides a baseline for the formant trajectories for men and women across a broad range of dialects of Standard American English.