Studio Ceiling insulation questions

First, it is my understanding that a vapor barrier in walls/ceilings between living spaces should be avoided. Check with a competent builder for the correct answer.

Now to add to the confusion, we talk about using foil or kraft paper with bass traps to enhance LF performance, but we don't try to block water vapor from traveling between rooms.

About sound transmission between rooms, that is a different subject and requires different techniques than acoustic treatment. The main idea is that you need M. A. M. configuration (mass - air - mass) the two mass components are typically drywall of 2 to 3 layers thick and should be vibrationally isolated (not touching each other). The "air" layer is where the insulation goes but this insulation will not treat the room acoustics, you'll still need treatment on the inside of your room.

So...you can fill your joist space with fluffy and cover with fabric but that will do only a little bit for transmission. For better transmission isolation, add mass to the underside of floor between joists (if the upstairs is open and can be worked on, just add mass to the floor above, but that is usually impossible). Fill between joists with fluffy, then either build a room within a room OR easier, use RC (resilient channel) to isolate the ceiling layers of drywall from the joists. Check with your builder to see if the existing structure will carry the additional load.

After the room in a room is finished and sealed etc. you can start treating the inside of the room. For details about "sound proofing" (it's in quotes because there is really no such thing), read this book. www.amazon.com/Home-Recording-Studio-Build-Like/dp/143545717X