Listen room Insulation only

Nothing you can do will make a garage sound good.Good luck though.

Is it a heated garage?Does it stand alone?  If it has a common wall with the house you don't want another vapor barrier with a wall that already has one. This would create moister problems. Need more details!

This vapor barrier has been a source of controversy for 50+ yrs or more. If you buy into the idea, then use Tyvek. It may be cheaper. My whole point is that you do not want to be breathing the dust from fiberglass  insulation for long periods of time. It needs to be covered for habitation

Don't use fiberglass.  Roxul is awesome stuff.  I totally agree with artemus and cover the walls with Tyvek.  Not only will it stop fibres, it will keep everything cleaner and look finished.  
You do realize the sound will really bleed outside...?

This vapor barrier has been a source of controversy for 50+ yrs or more ? .https://www.certainteed.com/insulation/resources/do-i-need-vapor-barrier .Where is the controversy? this is standard buliding practice!