Bit of music expected with boat race coverage (6)

I believe the answer is:

masked

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'bit' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

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(Other definitions for masked that I've seen before include "Blocked out, disguised" , "With covered face" , "Unseen" , "Disguised, covered" .)

I've seen this clue in The Sunday Times and The Times.

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