Problems with S/PDIF

R

Rolf Molini

Hello board,

currently I'm trying to connect my surround sound equipment to a Windows Media Center Edition PC and I'm experiencing constant
problems with that. I decided to put this post in here because I think this is an issue not specific to MCE but rather to Windows
XP.

The PC contains an NVIDIA nForce Audio chip with hardware decoder included, so there is a S/PDIF-output as well as 3 stereo jacks
for analog output of front, rear and center/subwoofer. My surround sound system (SSS) contains only analog inputs (3 pairs of
RCA-plugs).

The first try was to use adapter cables between the analog stereo-output of the PC and the analog input of the SSS. The nForce
audio-chip is controlled by an NVIDIA-applet called nMixer. Whatever configuration I chose there, it was not possible to get any
sound to the center speaker. The speaker itself and the amplifier work fine. Sending white noise to all speakers from within nMixer
lets all 6 speakers respond correctly. Only when real sound is to be transmitted, the center speaker will receive no signal from the
nForce chip (I can see that in the applet in a mixer, where all channels but center receive a signal).

I suspected the nForce-chip (to be specific: the audio decoder) to have a problem with the center channel. So I bought an external
audio decoder from Creative (DDTS 100) and connected S/PDIF-output of the PC to it and the analog outputs of DDTS 100 to the SSS.
To my surprise, the result is exactly the same. Sending test signals (this time from DDTS 100) to the SSS lets all speakers respond.
But sending real sound from PC to DDTS 100 and then to SSS leaves the center speaker silent.

Now, I'm asking myself if there is a general misunderstanding on my side. If not, might it help to use a PCI-audio adapter instead
of the onboard chip?

Thanks for any help

Rolf
 
R

Rolf Molini

Here are some more details about the problem:

With a stereo earphone I checked the three outputs of Creative DDTS100 (front, rear, center/subwoofer) while being connected to the
PC via S/PDIF. Running the usual media programs (like WMP or MediaCenter) only the subwoofer channel is fed.

After that I tried to play some music with Cyberline PowerDVD. And indeed, if (and only if) I activate audio expansion (called CMEI)
in PowerDVD configuration, suddenly the center channel is working.

Thus it seems to me, that it is a problem with the nForce drivers.

What seems strange to me is that - although there are two components connected which should turn simple stereo sound into a 5.1
soundfield, namely the Creative DDTS 100 and the Surround Sound System - the center channel still depends on some software within
the PC.

Regards
Rolf
 
R

Rolf Molini

Hi board,

seem to have found a way to work around the issue.

I reversed the nForce drivers back to a version where NVIDIA nMixer was not yet included but the older so called "audio control
panel".

There a LFE-channel for subwoofer and a center channel can be created and now subwoofer and center speaker work fine.

Question remains, why - when upgrading to the latest nForce drivers and installing nMixer - these features are gone. In nMixer the
distinct configuration possibilities for channels are not present anymore but a huge bunch of "environments" (about 30, from
"earphones" over "big hall", "arena", "club", "concert hall" and so on).

When you play around with this "environments" channels like rear or center/subwoofer come and go without order or system (at least I
could not discover such).

For the time being I will safely avoid upgrading the nForce drivers and remain happily with audio control panel.

Regards
Rolf
 
R

Rolf Molini

Hello Michael,

no, it doesn't seem to be a matter of connectors. As I described, the center channel was not provided with a signal from inside the
nMixer software itself (the center bar in the Mixer applet did not show any activity at all) when audio was processed.

However, when the nMixer applet sent test signals to all speakers, center channel received white noise very well... only then the
center bar of the nMixer was active.

Well, I suppose this is indeed a software bug of NVIDIA nMixer and - as you may have read already - reversing back to drivers where
nMixer is not included resolves the issue.

Best regards

Rolf
 

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