Possible Clues:

• Surrealist painter to urge 10 to play in rapid progression
• Chord played spaced out
• A pro, I suspect, about to encourage noted exercise
• Pianist's passagework
• Chord type
• Piano exercise
• Concert run?
• Chord on harp eg Giovanni included
• Split chord severely disrupted opera gig
• Encourage ten, it appears, playing rap first, to play in quick succession