Vorperian, PhD, H. K., and D. Bolt, PhD. Quantitative and Descriptive Comparison of Four Acoustic Analysis Systems: Vowel Measurements.
Burris C, Vorperian HK, Fourakis M, Kent RD, Bolt DM. (2014) Quantitative and descriptive comparison of four acoustic analysis systems: vowel measurements. Journal of Speech Language and Hearing Research. 57(1):26-45.