It also seems that the filter comes from using HD Audio in laptops, and it needed there. Basically, red line corresponds to 'headphones' selection, blue - for 'speakers'. The worst thing that only way to shut down this filter is selecting speakers, which mean you can not use headphone 3D virtualization (front-rear) with bass (It renders onboard HD Audio unusable for best gaming experience for me personally, I mean HD Audio with equalizer made Bass Boost can't replace my Creative X-Fi with 3D and real Bass Boost). It's good thing for some very old cheap piezoelectric headphones (check if you have one of those), but it's a disaster for modern good headphones. HD Audio seems to have a filter working for headphones. Try to detect headphones as front speakers.
