Did you try to compare it with the original files? I mean if they also are softly recorded, then that's just the way it is. And yes normalizing brings up the noise as well, but it will be the only way if this is standard level. If you do it through a normalizing or a volume control, the effects remain the same. You in both way lift all information in the recording upwards. I must say the recordings I made up to now, have not been the best quality always in volume or in sound/colour, but good enough to fix it in the mix. But well in fact this doesnot really answer your question I guess...

I'll be back...