Voice coach to the stars Gary Catona has worked with Andrea Bocelli, Sting, Whitney Houston, and Sara Bareilles, to name just a few. The system aims to help singers, public speakers, or anyone who wants to enhance the quality of their voice - including patients. I am not aware of any randomized controlled trials backing up his claims, but the presentation is inspiring.
Voice Builder on the App Store on iTunes
How to Develop A Manly Voice | Art of Manliness - YouTube http://buff.ly/1lFtPO6