Bolt, PhD, D., and H. K. Vorperian, PhD. Corner Vowels in Males and Females Ages 4 to 20 Years: Fundamental and F1-F4 Formant Frequencies.
Vorperian HK, Kent RD, Lee Y, Bolt DM. (2019). Corner vowels in males and females ages 4 to 20 years: Fundamental and F1-F4 formant frequencies. Journal of the Acoustical Society of America, 146(5):3255. doi: 10.1121/1.5131271.