When I first read your post I thought no one is gonna guess it from your description, but then I remembered a soundtrack I found fairly recently that has a female vocal going through it that goes "ahhhh-ahhhhhhh..." (high-to-low), "...ahhhh-ahhhhhhh" (low-to-high).
It's called "Girls" by a group called "Death in Vegas". I think that could be what you are after (and if it isnt, its a great piece of music anyway!).
unknown piece
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