What's new

Questions about C-Media audio ouput and general S/PDIF output (1 Viewer)


Second Unit
Jul 10, 2000
Recently I built a new PC with an Asus P4b266 motherboard (which has onboard C-Media chip CMI8738 with 5.1 audio) and a Pentium 4 1.6A.

I have been to the settings that allow you to choose 2-Channel/4-Channel/6-Channel output (6 Channel is L/F/R/SL/SR/Sub). I understand all that, but I am wondering how say 4-Channel, or 6-Channel sound gets routed to this chip for output. If I am running PowerDVD 4.0 XP, will that decode the audio stream from a DVD and output to the appropriate channels? I am betting NO.

So do I need some kind of software decoder that allows me to use the 4 or 6 Channel output correctly? I am trying to decide on some new PC speakers right now, and if I don't need a Dolby Digital and/or DTS decoder then it makes the decision easier. Since the computer is in the bedroom it will be used for watching DVD's and recorded TV. My video card is the ATI AIW Radeon 7500, which has S/PDIF output. My motherboard also came with both input/output S/PDIF connectors, so presumably I can record a digital stream, or maybe just use it for sound input.

So, the questions are...
1. How can I use the C-Media multi channel output for real 4-6 channel audio?
2. What can I use the input/output S/PDIF connectors for exactly?
3. Can I pipe the S/PDIF output from the Radeon into the S/PDIF input on the motherboard, then will the (up to) 6-Channel audio be split correctly for output?
4. Do I need a software decoder to decode the digital audio output by the Radeon?
5. Do I even need to use the S/PDIF output from the Radeon? Can I just use the analog outputs, or the S/PDIF output from the motherboard?
6. ???

Maybe I am not asking all the best questions right now, and I may have more questions based on some of the answers. I appreciate any help or information that you can give.



Dan M~

Second Unit
Nov 30, 2000

I just installed the ASUS P4B533 MB. You need an external decoder to use the 4.0 thru 5.1 options. Do you have the S/PDIF header for the digital output(I don't)? Take the digital output from the header into the digital input on your receiver/decoder. Anyone know a good place to pick-up the S/PDIF header for these MB's??

Hope this answers your ?'s


Second Unit
Jul 10, 2000
Dan, I got some answers to these questions over on http://www.avsforum.com/avs-vb/.
I have PowerDVD4.0 XP which has a DD/DTS(not sure about DTS) decoder built in. So I just have to select 6-Channel output from PowerDVD, and select 6-Channel output for my PC audio (which happens to be C-Media), then I can get the 6-channel analog audio output from the jacks in the back of the PC. I tested last night and it works fine.
I do have both S/PDIF input/output that is connected to my P4B266, it was an add-on that was included when I bought the motherboard from www.NewEgg.com. It has a small ribbon connector that connects right into the motherboard and is screwed into the back like a PCI card (but no card, just the metal piece with the in/out RCA connectors). I would expect that you can buy this for your motherboard as well.
Since I found the PowerDVD options for 6-Channel audio I don't need to worry about the S/PDIF output from the Radeon anymore, unless someday I connect it to a real receiver. I also now know that the C-Media will NOT decode and digital signal other than PCM (2-Channel only I think).
Thanks for the help.

Users who are viewing this thread

Forum statistics

Latest member
Recent bookmarks