Well, in 14. Century Renaissance just had started, so I would rather say, that first "romantic sounds" were used in late 1700's, by Ludwig van Beethoven. He was born in Classicism period, where also were Mozart and Haydn (3 classics of Vienna), but L van B in his several last works, piano sonatas and symphonies started to use romantical techniques and melodies. At least he was officialy both classic and romanticist. Maybe this answer isn't suitable, and I'm not an expert, but that's what I learnd in school.