Complex sentence: Until Season 7, it was never clarified he was aware of his impediment, however in "The Discovery Dissipation", when Sheldon mocks his impediment, Barry appears visibly hurt and tells Sheldon he has no control over it.
Split into simpler sentences: Until Season 7, it was never clarified he was aware of his impediment. However, in "The Discovery Dissipation", when Sheldon mocks his impediment, Barry appears visibly hurt and tells Sheldon he has no control over it.