The Unsound and the Black Capes Case

Experts claim the unsound is neither natural nor artificial. My guess is, it's synthetic, but I can't be sure until someone develops a more precise instrument to parse it. The most common myth is that the unsound summons or invites a demon into the world. An arch demon with a gentle voice? That doesn't sound all that scary. And this is why it's one of what you're calling the black capes cases.