Audio visualization script error?

Why won't this script work? I tried as much things to fix it but it fails. The script is suppost to make a logo union expand and shrink to the playbackloudness. It says "Sound is for a valid member of Music"

local MRV=game.Workspace:WaitForChild("Music")
MRV:WaitForChild('Logo')
while true do wait(.0001)
local a6 = MRV.Logo
a6.Size=Vector3.new(a6.Size.X, MRV.Sound.PlaybackLoundness / 400, a6.Scale.Y)
end

If anyone could fix it thanks!