Shrinking note is in key (10)

I believe the answer is:

minimising

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'shrinking note is in key' is the definition.
I can't tell whether this defines the answer.

'shrinking note is in key' is the wordplay.
'shrinking note' becomes 'minim' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'key' becomes 'g' (musical key).
'minim'+'is'+'in'+'g'='MINIMISING'

Can you help me to learn more?

(Another definition for minimising that I've seen is " Playing down".)

I've seen this clue in The Daily Express.

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