Barrientos Sandoval, L. E., and E. L. Cataldo Ferreira. “Synthesis of Sung Spanish Vowels in Lyrical Singing by Sopranos”. IEEE Latin America Transactions, vol. 19, no. 12, May 2021, pp. 2139-46, https://latamt.ieeer9.org/index.php/transactions/article/view/5293.