Dolby Advanced Audio effects doesn't work on Windows 8.1

Hi,

I have updated my HP Pavilion G6 2242sf to Windows 8.1 and the sound quality is not as good as in Windows 8 : In the Dolby control panel the equalizer works but switch the Dolby Advanced Audio checkbox has no effect so there is no more surround virtualization and the 3 effects "Movie", " Music", and "Voice" are not working anymore.

Now my laptop speakers sounds choppy... Could you help me to fix this ?