1. http://en.wikipedia.org/wiki/Singing
2. http://www.dummies.com/how-to/content/breathing-basics-for-singing.html
3. http://www.entnet.org/AboutUs/worldVoiceVocalWarmup.cfm
4. http://www.wikihow.com/Find-Your-Own-Singing-Voice#_note-1
5. http://voices.yahoo.com/10-tips-learning-sing-well-110289.html?cat=33