1930s novel clear regarding musical style (8,4)
I believe the answer is:
brighton rock
'1930s novel' is the definition.
(1938 novel by Graham Greene)
'clear regarding musical style' is the wordplay.
'clear regarding' becomes 'brighton' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'musical style' becomes 'rock' (rock is a music genre).
'brighton'+'rock'='BRIGHTON ROCK'
Can you help me to learn more?
(Other definitions for brighton rock that I've seen before include "Film" , "What offers colourful writing all through" , "... hard cylindrical sweet from the seaside" , "Book by Graham Greene" , "Work of fiction" .)