Re: insulating for sound
My suggestion would be to remove the drywall from the ceiling, exposing the joist bays. Insulate the cavities with standard fiberglass insulation -- not so much as a sound barrier (even though it will help), but as thermal insulation. That way you're not paying to heat your upstairs neighbor's condo.
Then, before installing new drywall, use sound isolating furring strips running perpendicular to the joists or isolation clips attached directly to the joists. The drywall attaches to this.
There is a considerable amount of sound telegraphed through the joists. By isolating the drywall from the joists you can eliminate most of this telegraphed sound.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.