AC97 is your sound card, AC3 is an audio filter. If you have it installed, you should have it amongst your filters, go search 'filters' on your computer but the AC3 control program is called 'AC3' simply and has a colorful icon. Maybe you can try the following path: C:\WINDOWS\system32(or 64)\rundll32.exe ac3filter.ax,config >> something like that, then follow the instruction about intensity.