When I was using steam I started to listen to some music using the music app from the windows 8 store. As soon as I used the <Win> + D shortcut to return to the desktop I noticed that my volume was 20% of what it was before. But luckily there is a simple solution to this problem.
- Press <win> + x and select Control Panel from the list
- Select “Hardware and Sound” from the menu
- Select “Sound” and select your primary audio device
- Select “properties” and go to the “advanced” tab
Deselect the checkbox “Allow applications to take exclusive control of this device”
- Restart steam
Windows 8 gives programs the ability to complete control of your sounds, therefore auto mixing them for you. For example: Lowering your music while you are playing a game etc.