Visitor who raises his voice? (6)

I believe the answer is:

caller

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'visitor' is the definition.
(caller is a kind of visitor)

I don't understand the rest of the clue.

(Other definitions for caller that I've seen before include "Visitor" , "One visits" , "Someone phoning" , "One paying a brief visit" , "Person on the line" .)

I've seen this clue in The Globe and Mail.

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