Using a Mac Pro, OS 10.6.8 to capture video with FCP6 with a Decklink Studio video card. Have been applying normalization gain for a couple years as part of our work flow. Recently I have begun to pick up fuzziness and a low rolling thump when I apply normalization gain. The capture plays back clean, and only picks up the noize when I apply normalization gain. When I undo the filter, it goes back to good audio.
I have checked for updates and updated the video card firmware, but the proglem still persists. Should I reinstall FCP6, or am I asking for a headache in doing so? Have you heard of such a problem?
Normalisation increases the gain of the audio so you may well simply be hearing the raised noise floor that is subtle at the original gain. After normalizing, if you reduce the gain of the normalized file to match the level of the source, do they sound identical? They should. I have trouble seeing how this operation could cause artifacts as it is simply a gain bump to bring your audio's highest peak to the desired level. I'd first try normalizing using other software to isolate the issue to either the source audio or the actual FCP normalisation. If it isolates to FCP, cleaning prefs could heal it. Maybe.
I would question why this is part of your workflow, though. Since the gain change is based on peak level only, which can have little relation to the average level, especially if there is mic handling noise involved, it is not that useful. Adjusting the gain while you edit or mix to your desired output level, which you'll do anyway with normalized files, saves you an operation and ensures you work on the source material. If the material goes to audio mix, we always prefer to receive non-normalized audio. Just a though.