Well, to begin with there’s a difference between sound proofing a room and simply treating a room for reflections and standing waves. I was talking specifically about the latter, which can be achieved rather easily and cost-effectively. Sound proofing is a whole other animal that requires a lot more in terms of materials, money, design, etc. For the purposes of what OP is doing (one guy recording a sax), sound proofing isn’t necessary at all. Hell, even for what I do, which is quite a bit more involved than recording a single instrument, it isn’t necessary either.