I'm in the process of renovating the 2nd story of my New England 1.5 story cape-style home. New OSB subfloors are down with Liquid Nails and deck screws over 5 weeks ago. I'm on to flooring now. I don't have much experience with wood flooring, so I'm not sure what my best option is for reducing traffic noise from upstairs into the rooms below. I'm not too concerned about moisture, except moisture content of OSB. The house has forced hot air heating. Can I use a felt cushion underlayment designed for floating floors in a nail down application of solid hardwood? Does rosin paper act in any way as a noise barrier?
You probably missed "the best option for reducing noise to below" if you put down new subfloors and didn't put insulation under them (assuming you actually removed the old subfloor and had open joists.) Your next-best option would be to blow in insulation from below.
If you are already committed to nail-down flooring, I don't think the underlayment will make much difference, as the nails will transmit sound into the structure. An actual floating floor on the thin, dense foam underlayment sold for that purpose would be the best option on top of the subfloor for traffic sound reduction - or a "no shoes on the second floor" house rule.