Typically, standard definition is not a comparable picture to an HD picture. Images can be blurry because standard definition is 480 lines of resolution being shown on 1080 lines of resolution. While there is processing already happening to improve the picture quality, there is a limit to the upconverting, which may explain some of the symptoms you describe.
The audio difference is a result of the broadcast. We don't control the audio difference that is transmitted.
My samsung 52 B750 is 6 months old and Iam not satisfied with the picture quality. Non HD channels are not good . If you stand close to the TV the picures are blurry. Also when scene is changing it takes few seconds to focus and then the picure gets better. there is rings around names and letters. I have Dish network . also audio raise after Tv is on for sometime. Please help me . I tried the picture settings from samsung site too. HELP