Possible Clues:

• Style of operatic singing, as that of Callas, say
• Lyrical operatic style
• Smooth operatic style
• Smooth singing style
• Lyrical singing style
• A style of operatic singing
• Deficient in decibel, can't opera be sung like this?
• Type of singing small Tom, say, is able to produce
• Noble act excitingly conveyed in style of singing
• Singing style