Is it the basic sound? The technique? The musicianship? The sheer virtuosity? The perfect marriage of music and text? 

Greatest Voices of all Time Photos © Pavarotti: Decca/Terry O’Neill; Siepi: Decca; and supplied

Perhaps...

This article is only available online for Limelight subscribers. LOG IN now or SUBSCRIBE to gain access and you could win a double pass to the Huntington Estate Music Festival.