PINGHIRIAC, Georgeta. “MANDATORY TECHNICAL ELEMENTS IN THE METAMORPHOSIS OF THE SINGING VOICE”. Studia Universitatis Babeș-Bolyai Musica, vol. 56, no. 1, June 2011, pp. 109-12, https://studia.reviste.ubbcluj.ro/index.php/subbmusica/article/view/8914.