I have had iOS 7 through all the betas on my iPhone 5. One feature I liked was Siri's more natural sounding voice. I passed my iPhone 5 down to my partner and got a 5S today but on the 5S, Siri sounds very robotic. Asking the same question on the 5 and the 5S is a really noticeable difference. Any idea why this would be happening or how to fix it?