Chú thích Âm vực

  1. 1 2 McKinney, James (1994). The Diagnosis and Correction of Vocal Faults. Genovex Music Group. ISBN 978-1-56593-940-0
  2. 1 2 Appelman, D. Ralph (1986). The Science of Vocal Pedagogy: Theory and Application. Đại học Indiana Press. ISBN 978-0-253-20378-6