I was reminded of this when I saw this pic today - with diffuser/absorption panels over the windows. (They're moveable. His standard diffuser panels, attached somehow to the window frames, I suppose.)
Jesco Lohan | @jescolohan Instagram
Some interesting pics - I like seeing pics of home studios, I got to this from his Youtube video on room acoustics.
I'm just going to do some panels like this, which is expensive enough for me, but I'm concerned about them getting dirty, the fabric covering, so maybe just acoustic foam, at least I could just unhook them them and wash them in the bath.