1. Ahn, H. Y. (1995). Assessment of voice. Seoul, Korea: Jin Soo.
2. Bang, Y. I., Min, K., Shon, Y. H., & Cho, S. R. (2013). Acoustic characteristics of vowel sounds in patients with Parkinson disease. Neuro Rehabilitation, 32(3), 649-654. 10.3233/NRE-130887 23648619
3. Bhuta, T., Patrick, L., & Garnett, J. D. (2004). Perceptual evaluation of voice quality and its correlation with acoustic measurements. Journal of Voice, 18(3), 299-304. 10.1016/j.jvoice.2003.12.004 15331102
4. Boersma, P., & Weenink, D. (2014). Praat: Doing phonetics by computer (version 6.0.30) [Computer program]. Retrieved from http://www.praat.org
5. Boone, D. R., McFarlane, S. C., & Berg, S. L. V. (1988). The voice and voice therapy (4th ed.). London, UK: Prentice Hall.