Lyutskanova, Doroteya. “Vocal-Pedagogical Guidelines to Help Methodological Work With Mutating Voices”. Young Scientific Music and Dance Forum : Conference with international participation, no. 13 (September 1, 2020): 82-91. Accessed April 21, 2021. http://ojs.nbu.bg/ojs/index.php/YSMDF/article/view/389.