if you're trying for complete sound proofing, that's very expensive and unlikely to succeed without professional help. did i mention it's expensive?
if you're after the more reasonable goal of sound reduction, you have to decide how much is acceptable in the situation. unless there's a baby sleeping in the next room, i've gotta think that you don't need to go to the trouble/expense of special studs, etc.
sure, you can go crazy and isolate walls, offset studs, etc. but again, unless you're trying to set it up so you can practice after everyone's asleep, just mitigating it should be fine.
sheetrock isolation is primarily for bass. i'll say it again: there is very little bass content to deal with here. you Do have large amounts of high mids and highs to deal with. isolating the sheetrock isn't going to affect that much.
absorption panels on ceiling and walls will certainly help. you don't need anything fancy, if you google sound absorbing panels you'll come up with some materials you can readily find at Home Depot that will help considerably. if it's easy to do, putting some regular home insulation in the walls will also help. sure, every layer of sheetrock will help, but how much do you want to spend? maybe you should try it first and see whether you need more. but don't do that without the absorption in the room, that alone will help at least as much as anything else you do.
visit the Auralex site -- they have a lot of info on what is (a) scientifically correct, and (b) what is practical and works.
