Voice of gangster? (7)
I believe the answer is:
soprano
I believe this clue is a double definition.
'voice' is the first definition.
(I've seen this before)
'gangster?' is the second definition.
(I've seen this before)
'of' acts as a link.
(Other definitions for soprano that I've seen before include "chorus girl, perhaps" , "High singing voice" , "gangster" , "(Singer of) the highest vocal range" , "Singer who aims high" .)