No it isn't. In fact, unless you de-couple the floor from the existing construction, ROOM within a ROOM technique is a waste of money and time.
The best bang for your "buck" is using Resiliant channel and 2 layers of 5/8" drywall. Not easy to do CORRECTLY...but I submit it IS the "best bang for your buck". PERIOD. Add more mass to the exterior, caulk all existing air leaks, Use a DOUBLE Solid core door system, and build a DIY decoupled floor system utilizing 1/2"carpet underlayment, 3/4" MDF, and a layer of laminate flooring. However, when you "soundproof" a structure, you "airproof" it at the same time. Which, if I remember correctly, even musicians like to breath. This means, now you must PENETRATE this "airproof" envelope to allow fresh air in.....which is a whole nuther' problem, which there is no need to go into at this point.