Thus, playing D and E flat around piano, it creates effect on one? (4,5)

I believe the answer is:

soft pedal

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But I can't explain it at all! Could you help me understand?

(Other definitions for soft pedal that I've seen before include "Piano lever" , "Play down" , "piano part" , "Subdue" , "moderate" .)

I've seen this clue in The Times.

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