These are mainly 2 x 2 panels glued to walls, made up of various materials, usually the same foam used in recording studios wrapped in fabric. (moneysense.ca)
In other words, I've been in and out of top recording studios for over a decade. (thewirecutter.com)
I have created and outfitted an in - home recording studio with hand - picked software, hardware, and sound equipment. (resume-now.com)