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.
Maybe you can see an association between them that I don't see?
'turn up very loud' is the wordplay.
'turn' is a reversal indicator.
'very loud' becomes 'ff' (musical abbreviation).
'up' written backwards 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" .)