Forgotten opera thrills with its high notes

Vivaldi's Griselda, with three castrati roles, will test modern audiences, writes Joyce Morgan.

They were the rock stars of their time with salaries as high as their voices - and egos.

Castrati could send opera companies broke with their lavish demands. The singers referred to as nightingales were in demand for their vocal dexterity.

Yet when the musicologist Erin Helyard teaches classes about the unique musical phenomenon, he knows what the first question will be. It won't be about the sound of their voices or repertoire.

''Students want to know how they were castrated,'' he says. ''They want to know the details.''

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