AC3Filter is a DirectShow decoder needed to play DVDs and AVI files rendered with AC3 soundtracks. It controls gains, stream info, levels, the mixer and other settings, also making possible Multichannel and S/PDIF technology. DTS files and raw ones can’t be open without this filter. Actually, you won’t be able to play any AC3 or DTS file without this filter, no matter whether the track is ripped from AC3/ Audio CDs, DTS/ Audio CDs or PES DVDs. After a simple installation, all AC3 files you may have will be assigned to this filter. All DirectShow players use this decoder, so you won’t be asked to install another one.
On the other hand, chances are that Media Player Classic will need special care after the installation of the AC3 decoder. A check at Internal filters (View > Options) solves the problem fast.