Pop diva Mariah Carey's penchant for sleeping in a room full of humidifiers the night before a concert is a vocal tip she learned from late soul great Luther Vandross.

The singer has often been ridiculed for her vocal demands, but she insists she has to take care of her voice.

She explains, "I sleep as much as I can the night before (a show). We have to sleep to hit the notes.

"I need humidifiers when I sleep because it's good for my voice. Luther Vandross, God bless him, told me that."