Fixed! Thank you youtube master wow, I had to put a modification at the end to make it not glitch out and be weird, thank you!
while true do
wait()
if game.Workspace.NPC.Head.speach.PlaybackLoudness <= 65 then
game.Workspace.NPC.Head.Mouth.Texture = "rbxassetid://2801767831"
elseif game.Workspace.NPC.Head.speach.PlaybackLoudness <= 75 and game.Workspace.NPC.Head.speach.PlaybackLoudness > 65 then
game.Workspace.NPC.Head.Mouth.Texture = "rbxassetid://2801751501"
elseif game.Workspace.NPC.Head.speach.PlaybackLoudness <= 85 and game.Workspace.NPC.Head.speach.PlaybackLoudness > 75 then
game.Workspace.NPC.Head.Mouth.Texture = "rbxassetid://845217767"
elseif game.Workspace.NPC.Head.speach.PlaybackLoudness <= 95 and game.Workspace.NPC.Head.speach.PlaybackLoudness > 85 or game.Workspace.NPC.Head.speach.PlaybackLoudness > 75 then
game.Workspace.NPC.Head.Mouth.Texture = "rbxassetid://907601394"
end
end

1 comment
If this is a Server Script, then PlaybackLoudness will always be 0 since there is no audio output on the Server, this needs to be run from the Client, use a LocalScript