1. Vocal Function Exercises;Stemple,2006
2. Lessac-Madsen Resonant Voice Therapy Clinician Manual;Verdolini-Abbott,2008
3. Lip and tongue trills: what do they do for us;Titze;J Singing,1996
4. From song to speech: what humming can do for you;Gregg;J Singing,1996
5. Lip trills and raspberries: “high spit factor” alternatives to the nasal continuant consonants;Nix;J Singing,1999