An Etymological Dictionary of the German Language/Laut
Laut, m., ‘sound,’ from MidHG. lût, m., ‘sound, tone, voice, cry.’ — laut, prep. with gen., is a form of the subst.; lit. ‘according to the sound of, &c.; MidHG. nâch lût, e.g. der briefe, ‘according to the letters,’ nâch lût des artikels, ‘according to the article,’ then also simply lût des artikels. Orig. used only of the contents of documents read out.