Anyone ever soundproof a room?

[salejolie]

I'm contemplating the purchase of a duplex next year so that we can rent out one side and live in the other. I'm seriously losing my mind apartment living, and was thinking about what our options would be if it ended up sucking just as much. Insight?

[FoxInFiji]

We added some soundproofing on the wall between our master bedroom and the living room. We didn't want to lose a lot of floor space (ie double wall) so we added a second layer of drywall to one side of the wall using Green Glue. We also used a sound deadening caulk (or regular caulk works too) between all of the gaps/seams of the drywall and framing.  Then we insulated the wall because it is way cheaper than the foam soundproof insulation we were finding. 

ETA:  Here is some good examples of soundproofing options:
www.soundproofingcompany.com/soundproofing101/4-elements-of-soundproofing-for-construction/