Garage Listing room

Since your walls aren't yet finished, there are a few things that are relatively easy to do right now while the framing is exposed. There are various construction techniques and materials that will help reduce sound transmission, both outside noise getting in and inside noise getting out. Which ones will work for you depends a lot on how things are laid out and where the noise is coming from/going to. The garage door I would think will be a major one. You will have to decide either replace it with a wall or seriously modify it to be more like a wall.

Also be sure to run your one dedicated line now before sheetrock. One line direct to wherever your system will be, another circuit for all other outlets and lights. 

There's a lot of options. Some like 5/8" sheetrock and single dedicated line cost next to nothing but deliver big time. Others, well you can spend thousands and not hear more improvement from a $200 fuse. So don't sweat the room. 

Without modification it's probably going to be a fairly dead sounding space due to all the exposed insulation. Are you willing to do modifications or would you need to use the space as-is? 

Use 5/8" sheetrock, it blocks like twice the sound of 1/2" for almost no additional cost.

That just isn’t true, sorry.

An STC (sound transmission) rating for a ’standard’ wall with 1/2" drywall on both sides is about a 33 STC rating, an insulated wall with *two layers* of 1/2" drywall *on both sides* is about 44, a wall with 5/8" on one side and *two* 5/8" layers on the opposite is about 55. We still have not achieved ’twice’ the stc rating, and we are well beyond what an existing 1/2" on the existing interior wall, and a new 5/8" layer on the garage would achieve, but it wouldn’t be as effective as two layers of 1/2" on both sides, an increase of only 11 STC points.

Can you achieve twice a standard 2x4 with 1/2" drywall 33 STC rating? Yep, you can get to 50-60, but not with a single layer of 5/8". Would it help? Yep, but not in reducing the transmission by 1/2.

My stereo room is above the garage. On the advice of a specialist I was able to add a floating sub-floor when the house was built.  On top of the standard 3/4" plywood floor, I added a layer of roofers felt covered by a 1/2" plywood layer scewed into the first layer, not into the studs. I also had the wiring for the  equipment outlets direct to a sepatate 20A breaker.

Please do yourself a favor, read my first post again. Specifically,

Usually only people who have actually been through this process know these things. So be careful, because a lot don't, but act like they do.

So for example when I say something like blocks twice the sound, that is because when you build it you will notice about half the sound getting through. If I wanted to sound all snotty and impressive I could spout dB specs all day and all night. This is the difference between trying to inform and trying to impress. Really wish the BSD types would catch on.