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What separates opera singers from other vocalists?

12 June 2014 Last updated at 11:01 BST

Opera "shows humanity at its greatest", American mezzo-soprano Joyce DiDonato has said.

She explained to BBC Radio 4's Today programme that the art of an opera singer is to perform without amplification, often for hours at a time.

Ms DiDonato added that it was this skill, above all, that separates opera singers from other classical vocalists.

First broadcast on BBC Radio 4's Today programme on Thursday 12 June.