The translations give ‘honourable’ or ‘pure’ for ‘lauter’, but ‘louder’ makes more sense. Does ‘laut’ have a comparative ‘lauter’?
“louder” is correct.
I never used the world to mean “pure” or something similar. If you read a German word, and it sounds similar to an English one, there is a high chance that the meaning is indeed similar. 
(Another meaning of “lauter” is slang and would mean “a lot of”. )