T. ŁĘTOWSKI, L. ZIMAK, and H. CIOŁKOSZ-ŁUPINOWA, “Timbre differences of an individual voice in solo and in choral singing”, Arch. Acoust., vol. 13, no. 1-2, pp. 55–65, Jul. 2015, Accessed: Jun. 10, 2025. [Online]. Available: https://acoustics3.ippt.pan.pl/index.php/aa/article/view/3061