Turn up very loud that which is very soft (4)
I believe the answer is:
puff
'turn up very loud that which is very soft' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'turn up very loud' is the wordplay.
'turn' says the letters should be written in reverse.
'very loud' becomes 'ff' (musical abbreviation for 'fortissimo', very loud).
'up' reversed gives 'pu'.
'pu'+'ff'='PUFF'
Can you help me to learn more?
(Other definitions for puff that I've seen before include "Pull" , "publicity" , "Gasp" , "out of which pants come?" , "Light pastry; advert" .)