(from Ask Ed) "I have a condo and the inside walls seem to have no insulation between units. How can I add soundproofing?....."
Link: Ed Del Grande: Ask Ed -- Sounding Off on a Condo Issue (HGTVPro.com)
I want to add that soundproofing is so important! If you're building or remodeling, thinking about using a noise baffling insulation; a friend advised us to, but when the time came, and we had to think about cost, we didn't do it. And there is one bedroom/bathroom wall that we would have put that insulation in, no matter what it cost!!