Cedar planks will not provide any benefit for anyone in the equation. For the people you don't want to disturb, it won't absorb much of the sound. And for you and the band, it will be extremely reflective, prone to feedback, and likely a poor space to record in, especially if it's a simple square room. I'm not sure what your budget is, but it will be wasted on cedar planks.
Cort Ammon and Maxwell Smart have good suggestions.
If your budget is tight/free, we always looked for used carpet. It's regularly available in dumpsters behind carpet centers. We let the staff know we were looking (so as not to worry them!), and you want to snatch it ASAP, certainly before it rains or before cats get into it, etc. Get as much as you can on the walls and get as much as you can on the floors. This will improve the acoustics in your space, but it won't make a dent on the volume that penetrates into the rest of the house!
If you have some ca$h to throw at this, frame up a room-within-a-room like @CortAmmon suggested (make it triangular or unusually shaped, at least not square) and then properly carpet the inner room, with padding below the carpet. Then hang drywall for the inner room. The thicker the better. Consider using two sheets! And if it were me and some hypothetical lottery winnings, I'd carpet the walls too, again, with padding. Next time you're in a movie theater, notice how they have fabric on the walls..
Finally, if you still have $$$ left, try lining the ceiling and walls of the outer room with natural cork, which you can get in 4'x8' sections of varying thickness, however this is not cheap. I'd prioritize the ceiling and the top parts of the walls in the outer room.
You're going to have to throw some money at this to create a sincerely isolated room. I can tell you from experience that hanging used carpet on the floor and ceiling might make the room less prone to feedback and more record-friendly, but it will not come remotely close to silencing your drums to the outside world! In that regard, Paul Logan is right!