Ugh, now I know why I've used ATI for the HTPC projects (and nVidia everywhere else, but I digress...)

Useless filler background: I have this MSI PCIe 8400GS I borrowed not long ago to test the judder/stutter stuff from the other threads.  He didn't want it back, so it's mine now.  Since I had an extra CPU, some extra RAM, etc, I figured why not just buy a motherboard and a case and make a cheap HTPC for the guest room, that way family and guests have instant access to all 300+ of our DVDs.  I bought another 480G-based Gigabyte board, forgetting how horrid it was for HD with the Athlon 4850e CPU.  Bummer, right?  So I decide to use the 8400GS.  Of course, I need to order an HDMI kit for it, so I did, and it came today ...

I cannot get the audio to work properly over HDMI and need assistance.  The HDMI picture itself is fine, the card recognizes it's HDMI, all good there.  I hooked up the 2-wire cable to the video card as directed, and attached it to the motherboard's SPDIF and GND pins.  I get audio, but it's HORRIBLY garbled.  You can occasionally hear some actual tones, but for the most part it's clicks and pops and noise. 

There are 5 pins on this motherboard.  VCC, SPDIF, GND, SPDIFI, GND.  "SPDIFI" is input, "VCC" is power, so I would think I have it correct here.  "SPDIF" and "GND".  I don't have the wires backwards, trust me, so what gives?  Isn't this all you're supposed to have to do for nVidia cards?  Should I be doing something with "VCC"?  I really and truly think not, but I'm stuck.

Advice?  It really does make you appreciate ATI's onboard HDMI audio, even if it's a driver nightmare. lol.

Man, I hate bumping threads, I really do, but I was hoping to catch the weekend crowd here.  I promise not to bump again, if nobody knows nobody knows :)

All you need is SPDIF and GND. Are you using a cable supplied by the manuf, are did you make your own? Are you sure you don't have the polarity reversed? I think there is a small indicator on the SPDIF plug on the video card - that is where the SPDIF side goes, other pin is GND.

Using the manufacturer's cable.  I've tried it with both possible polarities.  One way makes nothing at all, the other is when I get the pops and noises rather than proper audio.  The DVI->HDMI adapter is nVidia as well, it's not a generic.

One thing I didn't try was output level.  It does almost sound like you might expect it to if you were completely overpowering it. 

Thanks for the input!  I can't believe anyone dug this back up for me!!!

Did you ever figure this out? I'm thinking of purchasing the 8400GS for a cheap Vista HTPC. I'd go with PCIe or AGP if the PC had one. Thanks!

I'm running a XFX 9600GT OC with the same SPDIF setup - made the cable myself out of an old CDROM sound cable - sound is FANTASTIC!

I never personally did figure it out, I ended up switching to an ATI HD4550 and dumping the 8400GS altogether.  The ATI card works dandy, but only at 44.1KHz.  I'm assuming that the problem was more with the TV at this point than the 8400GS.

 hi im assuming the ati hd4550 does not need the s/pdif audio connection and passes audio up the hdmi via the pci-e connection...???? i have same problem nvidia 8400gs with s/pdif connector on board but i dont have s/pdif output on mobo or sound card...!!!!

 I have the 8400GS and built a custom cable using the advice in this thread and it works perfectly. Just make sure you use the SPDIF and Ground pins from your sound card, and if it doesn't work reverse you polarity. If it still doesn't work you likely have either a defective sound or video card.