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I recently upgraded to Windows 7, mainly for the upgrades to Windows Media Center.  One problem I discovered was with digital audio from HD channels and DVDs/Blu-Ray discs.  I wasn’t able to control the volume using the media center volume (system volume).  I could only adjust the volume on my stereo.  I found an article on the Hack Windows 7 Media Center site that discusses how to pipe all audio through AC3Filter to enable adjusting gain and using an equalizer before the audio is output from the machine.

The two main steps are to first setup media center to use AC3Filter then configure AC3Filter as you like.

More detailed steps are as follows:

1. Install AC3Filter
2. Install the ‘Take Ownership’ registry hack
3. Take ownership of ‘C:\Windows\system32\MP3DMOD.dll’ (right click -> Take Ownership)
4. Rename ‘C:\Windows\system32\MP3DMOD.dll’ to ‘C:\Windows\system32\MP3DMOD.dll.bak’
5. Get the CLSID of AC3Filter using Radlight’s Filter Manager.
6. Set the registry key ‘HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\ CurrentVersion\MediaCenter\Decoder\PreferredMPEG2AudioDecoderCLSID’ to the CLSID from the previous step.

A restart may be required here.  After doing this, all audio for media center should be piped through AC3Filter.  Now one can adjust the settings in AC3Filter to adjust gain, surround settings, equalizer settings, etc.

I’m now able to control all my audio using the system volume rather than my stereo’s volume.