Pronounced FREED-rikh. (note: 'kh' is not the exact pronunciation here but it is closest to the German 'ch') This name was very common in Germany until about 50 years ago. Today it is rarely used on babies. [noted -ed]
Actually, I know someone with this name who pronounces it like "Fredrick". He really hates it when people pronounce it "Freed-rick" but I'm not sure if he's pronouncing it right himself.
http://www.nordicnames.de/Aussprache.html.