in regard to Daisy's voice what significance does this quote have "When the melody rose her voice broke up sweetly following it in a way contralto voices have and each change tipped out a little of her warn human magic upon the air."

I don't think Daisy's voice was like this. The quote reflects Gatsby's infatuation with Daisy. For Gatsby, Daisy was perfect. Her voice was angelic and her being exquisite. THe Daisy that Gatsby loves really doesn't exist, he merely conjures this fantasy in his mind.