Sound barrier board or material for walls?

Julie
by Julie
Hi. We have one room in our house dedicated to a music recording studio. My husband is in search of the best, easiest, --& most economical-- board or material to attach to all walls to prevent sound coming in & out of the room. He found "Quiet-rock" as a good choice, but no one here carries it. He's looking for something besides cement board. He'll close off the window too and add this board/material. Any other material/board suggestions? Thanks!
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