Time to work on the internal SoundScreen insulation batts, covering all four walls and the ceiling.
The this the second stage of the insulation for the soundproofing process. Having the sound insulation material on both sides of the air gap of the room-in-a-room soundproofing concept, should have much better Sound Transmission Loss (STL) than Resilient channels and clips.
I can hear the difference already, every time i’m in the room.