Question: "What determines the category?"  Context: "The "soft" AC format has reinvented in the late 2000s/early 2010s as a result of its declining relevance, adopting a more upmarket, middle-of-the-road approach, with a selection of "oldies" (usually from the 1960s/70s onwards), primarily rock, jazz, R&B and pop music. Newer songs are more often (but not limited to) "easy listening" fare, this amount varying depending on the age of the station's target demographic."  Answer:
The answer to this question is:
the age of the station's target demographic