'aloud' and 'out loud' are for all intents and purposes synonyms. They both refer to sounds that are 'audible' or 'able to be heard'. For example, when trying to practice English, it is useful to read sentences aloud. Loud is an adjective that means a high volume sound. For example, the music is too loud. Loudly is the adverb form of loud (i.e., to scream loudly).

speak out loud; read out loud; scream out loud say it aloud; say it out loud; read it aloud; read it out loud I think that sums it up.