Postpone working out between quiet and very loud (3,3)
I believe the answer is:
put off
'postpone' is the definition.
(synonyms)
'working out between quiet and very loud' is the wordplay.
'working' indicates an anagram.
'between' means one lot of letters goes inside another.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'and' says to put letters next to each other.
'very loud' becomes 'ff' (musical abbreviation).
'out' with letters rearranged gives 'uto'.
'p'+'ff'='pff'
'uto' put inside 'pff' is 'PUT-OFF'.
(Other definitions for put off that I've seen before include "Postpone; distract" , "Throw" , "Don't ... ... till tomorrow what can be done today" , "'Never ... ... till tomorrow what you can do today'" , "Deter; delayed" .)