Sort out middle section of tune with composer (7)
I believe the answer is:
unravel
'sort out' is the definition.
(I've seen this before)
'middle section of tune with composer' is the wordplay.
'middle section of' means to look at the middle letters.
'with' means one lot of letters go next to another.
'composer' becomes 'ravel' (Maurice Ravel, 1875-1937).
The centre of 'tune' is 'un'.
'un'+'ravel'='UNRAVEL'
(Other definitions for unravel that I've seen before include "Unpick, untangle" , "Make sense of" , "Sort out" , "Come undone; solve" , "Disentangle knitted wool or solve mystery" .)