Opera group's paper read back in interval (8)

I believe the answer is:

semitone

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'interval' is the definition.
(I know that Semitone is a interval)

I don't understand how the rest of the clue works.

(Other definitions for semitone that I've seen before include "Short musical interval" , "Small musical interval" , "Small interval between notes" , "One twelfth of an octave" , "Interval between adjacent keys, on a piano say" .)

I've seen this clue in The Independent.

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