Soundproof material for a dedicated room

I'm thinking of converting one of my rooms to dedicated audio room. Since it's a condo and there are neighbours to the side of me on 2 sides, I'm trying to figure out what I could put on the walls to prevent the sound going next door. Can I get away with just gluing something on the walls or would it help if I built a wall on top of the existing one and put something inbetween. Looking for something that won't break the bank, but also something that is effective. Waf is non-issue. What soundproof product or materials would you guys recommend?

Thank you all for your inputs