Songdorn, T. ., and S. . Pongsarayuth. “‘Analysis of Singing Techniques and Interpretation of Four Last Songs by Richard Strauss’”. Rangsit Music Journal, vol. 18, no. 1, Feb. 2023, pp. 63-78, https://so06.tci-thaijo.org/index.php/rmj/article/view/248558.