1. Aronson AE. Clinical voice disorders. New York: Thieme, 1990.
2. Comparison of Voice Analysis Systems for Perturbation Measurement
3. Boone DR, McFarlane SC. The voice and voice therapy, 6th edn. Needham Heights, MA: Allyn & Bacon, 1999.
4. Colton R, Casper J. Understanding voice problems: a physiological perspective for diagnosis and treatment. New York: Williams & Wilkins, 1996.