I'm not much of an isolation expect, but these guys sure are:

http://www.soundproofingcompany.com/

Their Green Glue product is highly regarded, and they have lots of performance data and isolation advice on their site. So I'd start there.

--Ethan

If they are suggesting staggered and separated studs, ie a second wall but a hair separate, that is fine. And then the inner wall with the double drywall and greenglue.

major point: NO HOLES (in the wall structure. Not even one. All must be sealed, otherwise, you just wasted your money on the entire construction. Sound does not quite flow like water but it does come out of space as in when a bucket of water that has holes in it. So - no holes, no gaps, no leakage. None. Zip. nada. Ie, your ears nearly pop when someone closes the door to your studio and you are inside it.

At that popint the room will be HARD. that will give great bass, if of course, you then 'room correct' the resulting acoustics with something like Ethan's product.