Resolved: AC3 Audio/sound Dropouts (C-Media)

[wylee]

I've been trying to resolve my audio dropouts when watching DVDs with Dolby Digital or DTS soundtracks - I'd see my receiver "blip" as if the signal was lost for a brief moment. It drove me mad!

The soundcard I've been using is a cheapy Dynex 7.1 - not very sophisticated, but it supported SPDIF passthrough; I've updated the drivers and fiddled with AC3 Filter to now end, but my problem still persisted.

I stumbled across this project: http://code.google.com/p/cmediadrivers/ where dogber1 wrote his own WDM Drivers for C-Media 8738/8768 based soundcards to support bit perfect playback. Apparently, even though the standard C-Media driver that came with my card supports passthrough, it was still doing some processing on the signal I installed the drivers and suddenly my dropouts no longer are happening!

So, if anyone else is having this problem, give the drivers a try - if you use your computer for other activities (i.e. playing games), these may not be the drivers for you, but if you have a dedicated htpc it may fix your problem!

[LehighBri]

Great find. I have onboard sound on my Dell XPS 420. Do you know how I can tell if the onboard sound uses the c-media chip? The device manager under Windows Vista says the soundcard is "SigmaTel High Definition Audio CODEC" but it doesn't give much more than that.

[wylee]

Not sure if the Sigmatel uses C-Media chips. In XP, the device manager listed CMedia under the "Sound, Video and Game Controller"

In Vista, my XPS M1530 lists "Sigmatel High Definition Codec" - so I'm not exactly sure if they're the same chipset.

[wylee]

I believe the "SigmaTel High Definition Audio CODEC" uses a STAC chipset a 922x

http://www.sigmatel.com/products/pca.../stac9220.aspx

Depending on your system, this utility may be able to provide you a more detailed description on the hardware in you computer:
http://www.belarc.com/free_download.html