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 Windows Media Center part 3: Missing center channel    
 Dated:  Friday, October 10 2008 @ 09:13 AM PDT
 Viewed:  2,289 times  
TechnicalWhat to do when your Windows Media Center suddenly decides your 5.1 surround system only has two speakers.

We're having some friends stay the weekend, and I thought I'd get a copy of Iron Man to play on the new TV. I then discovered that somewhere along the line the media center had lost the ability to play Dolby Digital correctly. Playing a 5.1 movie on the media center gives me only the left and right channel. No center or surround. Great music and effects, no dialog.

I'm thinking it was a drive-by-night Winders update. I have the media center connected via optical to the AC/3 decoder, and in the past I just set it to 5.1 and forgot about it. When I brought up the SoundMax driver, it said I only had two speakers. When I tried to set it to surround, it gave me a "the application has encountered an error and must now close".

I uninstalled the driver, got the updated driver off the ASUS website, installed that, no joy. I looked through Media Center settings, but whenever I punched "audio", I get "media center has encountered an error and must now close". I have antivirus and antispyware going... Nothing there. Is Microsoft telling me I need to upgrade to Vista?

At this time, it's a good idea to hit the forums and see if anyone else has run into this problem. Feeding various combinations of "windows xp", "soundmax", "5.1" "missing center channel", I discover that *lots* of people have had this problem. The general consensus is that the SoundMax drivers are crap, and the only realistic way to get all channels sent to the SPDIF out is to download and install an open source Dolby Digital driver called "ac3filter":

Or on sourceforge:

This driver bypasses your audio driver and sends everything to the SPDIF out unmolested. As soon as I installed it, the readout on the Dolby Digital decoder switched from "PCM stereo" to "3/2 digital". Suddenly my surround channels came back, and with a little tweaking sounded better than they ever had. Amongst a lot of other things, ac3filter allows you to adjust both prefilter and postfilter settings of individual channels, so I was able to fix a level issue with my rear speakers at the same time, by making the postfilter levels a little hotter.

It looks like ac3filter will also do ac3 to dts translations either direction, so you can send everything to the dts decoder (if you have one, I don't) or send everything to the ac3 decoder.

Most of the complaints on the forums dealt with Windows XP Media Center Edition, but some were Vista issues. (Some reported that 5.1 was messed up in "vista home" but not "vista premium". Your mileage may vary. I don't know nuthin about Vista.)

Hope this helps. Even if you don't have a surround issue, ac3filter is worth a look for all the other little tweaks it can do.

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