ŁĘTOWSKI, Tomasz, Lidia ZIMAK, and Halina CIOŁKOSZ-ŁUPINOWA. “Timbre Differences of an Individual Voice in Solo and in Choral Singing”. Archives of Acoustics 13, no. 1-2 (June 30, 1988): 55–65. Accessed March 4, 2026. https://acoustics.ippt.gov.pl/index.php/aa/article/view/3061.