I've been messing around with sound alot lately and have found that all the materials these people have been talking about work in the right application. The key is dead air. Any time a wall or floor or ceiling connected together by todays standards , they will transmit sound. If you want to reduce the sound between two residences, the object is to eliminate the tie to each other. Two walls seperated by 2 inches of space and insulated with sound attenuation blanket insulation will stop or reduce some frequencies of sound. I used two layers of 5/8 inch drywall on each side of the wall whenever possible. The can be costly and time consuming , but if you want peace and quiet, It's up to you. The more you try, the quieter it can get!