Vulgar sound-track? (6)

I believe the answer is:

coarse

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'vulgar' is the definition.
(I know that vulgar can be written as coarse)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for coarse that I've seen before include "Rough in texture or crude in manner" , "Large-grained or rough to the touch" , "Rude, vulgar" , "Vulgar; not fine" , "Rude, base" .)

I've seen this clue in the Sydney Morning Herald.

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