Quiet is what it is. All bows make noise. Some are louder then others but they all make noise when shot. Noise travels at 850 FPS, or something like that. My fastest curve shoots a GT at 211 FPS. Sound will always get there before the arrow.
With that being said, I'm sure deer know what certian sounds mean if the area has seen hunting pressure. If you get your bow real quiet, they may not put it together that someone just put an arrow thru them untill it's too late.
Thats what I strive for. Any forgien noise will spook jumpy deer. Deer reflex's are extreamly fast. Notice how a deer will stop in it's tracks when you let out a quick whissle? get your bow noise down to a dull thud and it will have the same effect, at least that is what I have found.
JL