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Digital 5.1 problems

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  • Sound Cards
  • Components
Last response: in Components
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April 19, 2012 4:23:19 AM

Hello

So I am working on trouble shooting a computer running XP Pro on a server grade motherboard. Right now the computer has a Creative SB1040 sound card and will not produce a 5.1 signal out of the optical port. The speaker set is outputting to is a Samsung HTZ320 dvd player/receiver (5.1) but can only seem to get 2.1 out (R/L/Sub).

I was thinking that maybe the card is not capable of encoding proper formats for 5.1 so I have tried to swap out the card for a Creative SB X-Fi Titanium card which I know outputs 5.1. This resulted in still only a 2.1 output to the speakers.

I then tried to swap out the Samsung front end for another 5.1 HT system which I know to be able to output 5.1; only to yet again hear 2.1 sound. I spent a few hours messing with the creative audio control panel and the windows audio settings to no avail. I, just for s-and-g's hooked up the two receivers in tandem for a 4.1 system (analog connections) and was successful. Also, I tired to install the active Dolby/DTS encoder software, found through searching around, but the installer told me that the program wants at least Vista in order to install.

The second receiver has a little display on the front displaying what type of encoding is being used for the optical input and it shows Linear pulse-code modulation (LPCM) which is most commonly found with a 2.1 output but is capable of encoding 8 channels (7.1).

Does anyone have any ideas for my problem? (other than getting a new computer)

Thanks for your input

More about : digital problems

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April 19, 2012 8:37:40 AM

The consumer optical port is limited to 2.0 for uncompressed sound. To pass 5.1 you need DTS encoding, which is usually quoted in sound card specs (the Titanium seems to have it). The best way to test is to try a DVD with AC3 5.1 passthrough (for which the player itself should provide an option). If you can get 5.1, then look for dolby digital live (name used in Titanium specs).
PS: Are you sure it's 2.1 and not 2.0? Maybe the .1 is extracted by yout receiver from stereo channels.
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April 19, 2012 9:02:15 AM

What Mathew7 says is correct. If you want to send uncompressed audio to an external receiver you must use an HDMI or DisplayPort adapter. You can only send AC3 (Dolby Digital) or DTS if you want 5.1 or 7.1 audio. Some newer Creative sound cards have support for Dolby Digital Live which encodes what would normally be sent to the speakers into a 5.1 Dolby Digital signal and sends it to the receiver. However this is limited to 16 bits per sample and 48,000 samples per second (48Khz/16) so really high quality sound isn't always an option. I've tried it and found the quality to be lacking at times.

LPCM is certainly capable of handling up to 7.1 as part of its specification but Windows limits it to only 2 channel stereo. I'm not certain if sound card manufacturers are able to override this but as far as I know, none do.
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April 19, 2012 5:30:16 PM

Cosigned with the above two posts. SPDIF simply can not transmit uncompressed 5.1 audio. To get 5.1 passed over, you need to use a compressed format [Dolby Digital or DTS]. Most soundcards have the ability to convert uncompressed 5.1 to one of these two formats.
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April 22, 2012 3:41:19 AM

Thank you for the replies.

So now with all of that said, why does a movie file (.avi) with AC3 audio (6 channels) only output to two speakers? It audibly changes output characteristics but the sound is only driven from 2 speakers.

VLC player with the 5.1 audio channel selected
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April 22, 2012 4:52:15 AM

sharpiedpanda said:
Thank you for the replies.

So now with all of that said, why does a movie file (.avi) with AC3 audio (6 channels) only output to two speakers? It audibly changes output characteristics but the sound is only driven from 2 speakers.

VLC player with the 5.1 audio channel selected


If you're using the optical connection you will have to select the SPDIF Passthrough audio option (other filters have similar options). If you don't, it will be decoded by the software decoder and sent as uncompressed audio as if you were listening to it directly from your PC and not the external amplifier. Passthrough tells VLC not to decode the AC3 audio into its 6 channel components for playback but to keep it in AC3 and have the endpoint (your receiver) do the decoding.
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April 22, 2012 5:08:46 AM

Pinhedd said:
If you're using the optical connection you will have to select the SPDIF Passthrough audio option (other filters have similar options). If you don't, it will be decoded by the software decoder and sent as uncompressed audio as if you were listening to it directly from your PC and not the external amplifier. Passthrough tells VLC not to decode the AC3 audio into its 6 channel components for playback but to keep it in AC3 and have the endpoint (your receiver) do the decoding.


Are you referring to the 'use S/PDIF' toggle in the preferences>All>Audio tab or to manually switching all of the output modules (DirectX, File, WaveOut, etc.) to output through the SPDIF Out (Creative SB X-Fi) or am I just missing it completely?

Also, are there any python coders out there? :hello: 
Has anyone successfully outputted >2.1 audio using WorldViz Vizard? (might make a separate thread on this...)
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April 22, 2012 5:32:42 AM

>Are you referring to the 'use S/PDIF' toggle in the preferences>All>Audio tab or to manually switching all of the output modules (DirectX, File, WaveOut, etc.) to output through the SPDIF Out (Creative SB X-Fi) or am I just missing it completely?

I haven't used VLC in a while. Last I did I had to select it in the audio devices list. That does sound like the right thing though.

Simply choosing SPDIF Out as the playback device won't make VLC pass the audio through as AC3/DTS, all it does is tell it to send the audio streams to that device. It will still decode the AC3/DTS streams into 6 PCM streams and Windows will mash those into two and send those down via SPDIF.

You need to tell VLC explicitly that you have an external receiver capable of decoding AC3/DTS and that it should not do so itself (same rule applies to MPC/FFDShow/etc...). XBMC handles this quite nicely, others not so much.
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April 27, 2012 6:21:45 PM

Best answer selected by sharpiedpanda.
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