Sound Problem (not classic)

[destinationriver]

Hey guys,
when I start in some cars, the lower frequences (? don't know the english word for German "Drehzahl") have no sound. So just when shifting and the tyres. Here the video: I filmed it with my mobile, because I don't have a recording program for PC.

The cars are the Porsche 911 (997) GT3 and the Zakspeed.

Thanks for help

 

[Chris]

Does it do this with official content? If not, then it's probably because those cars need updating to make them compatible with the new FMOD build that Assetto Corsa currently uses.