laŭta

The obvious trap is that laŭta has nothing whatever to do with the preposition laŭ (according to). They look like relatives and are not, so laŭ mi means in my opinion, never loudly. Beyond that the root behaves itself: mallaŭta is quiet, laŭte is the adverb that does most of the everyday work, and laŭtigi is what you do to a radio. English speakers often reach for alta here because a voice can be high; in Esperanto alta voĉo is pitch, laŭta voĉo is volume.