Christy, V. A., & Paton, J. G. (1990). Foundations of singing: A text book in vocal technique and song interpretation (2nd .ed.). Wm. C. Brown.

Christy, Van A., and John Glenn Paton. Foundations of Singing: A Text Book in Vocal Technique and Song Interpretation. 2nd .ed. U.S.A: Wm. C. Brown, 1990.

Christy, Van A., and John Glenn Paton. Foundations of Singing: A Text Book in Vocal Technique and Song Interpretation. 2nd .ed. Wm. C. Brown, 1990.