Just download TouchBios(TB) from gigabyte's official site, install. When you install launch TB. The path you need is:
PC Status>overcklock>Advanced Memory Setings>System memory multiplier
set it to 16.00 done job, it's safe fast and you don't need the why!
But if you need it, it's probably Gigabytes fault , i had the same problem.
I forgot.. restart the PC after saving your settings.