It well be a language depending on how you define language, but the hypothesis I'm talking about rests on the assumption that most (Western) music is repetitive

It well be a language depending on how you define language, but the hypothesis I'm talking about rests on the assumption that most (Western) music is repetitive enough and with a small "vocabulary" enough to be uninteresting to newborns, and certainly not heard as a language simply because of the lack of variation. (Some pop music is worse than other types in this regard.)