1 2 Previous Next 21 Replies Latest reply on Jun 11, 2011 8:13 PM by parsec

    Why is the output from coaxial digital not 5.1?


      I own the Intel D975XBX2 motherboard. I remember in Vista 32 bit, which I had under this same motherboard, the audio output, when using the coaxial digital cable straight to my home theater receiver, was 5.1, as the receiver told me so. But now, under Windows 7 64 bit it's only two channel. Why is this? How can I make it output 5.1?

        • 1. Re: Why is the output from coaxial digital not 5.1?

          Its been my experience audio has always been a 64bit issue with this high dollar board, and intel stopped supporting it while it was still an infant

          • 2. Re: Why is the output from coaxial digital not 5.1?

            Coaxial and S/PIDF are always 2 chanel , it depends on the audio device you have it hooked up to ,  to do the decoding to 5.1 or 7.1 . But it always starts out as two chanel.

            • 3. Re: Why is the output from coaxial digital not 5.1?

              And further to what Robert's already written, the media being played needs to be 5.1 and encoded in Dolby Digital (your receiver also needs to be DD compatible). If it's the same one that worked previously under Vista, that wont be a problem.


              You may want to check the audio hardware manufacturers website (if there's nothing on Intels website) to see if there are updated audio drivers (although the default Microsoft Windows ones should work otherwise).


              There are sone demo AC3 files on this website http://www.lynnemusic.com/surround.html including a 5.1 surround test AC3. They play OK on my Win 7 x64 PC.

              • 4. Re: Why is the output from coaxial digital not 5.1?

                I cannot agree that a data stream on the S/PDIF output via coaxial cable or TOSLINK is always two channel audio.  Dolby Digital (DD), or AC-3, or Dolby 5.1 Surround uses the same physical S/PDIF interface as PCM (CD) audio, but the format of the data is different.  There are variations within the DD data which allows it to carry two channel audio only, but it may carry from one channel mono to the six discrete channels found in 5.1 DD surround sound, with the new DD Plus and DD True HD carrying up to eight channels of audio.  As Kiwi stated, the DD data stream must be decoded by a HT receiver, HT preamp/processor, or separate DD processor.


                Saying that the data in a S/PDIF data stream is always two channel implies/means that the other surround sound channels are derived from two audio channels, which is not the case with DD 5.1.  Dolby Pro Logic processing is another situation, which takes two channel stereo audio and creates a center, left and right surround, and LFE channels from it.  A Dobly Pro Logic enabled audio component is usually capable of configuring the number of resulting channels from it's processing.  A Dolby 5.1 channel capable audio component can also configure the number of channels of audio the user wants to use, but a standard DD 5.1 channel data stream contains six discrete digitally encoded audio channels.  They must be decoded and converted to analog prior to amplification of course, but they are not derived or created from two audio channels.


                The difference in the data stream between CD/PCM digital audio and Dolby Digital audio is the reason you cannot connect a DD data stream to the audio CODEC/DAC chip (Digital to Analog convertor) found in most PCs and have analog audio output from them.


                I am not familiar with the audio configuration in Windows Vista, but in Windows 7, you must enable DD as a supported format, as well as enable the correct sampling rate for DD (48kHz).  That may be done from the Sound option in Control Panel, after highlighting your Digital Output device, and then clicking the Properties button.  In the Supported Formats tab, you can enable DD and check the correct sampling rate (you may check as many as your HT receiver or processor supports).  In that tab is a button to test DD decoding, which will play a series of notes that you will hear through your speakers if all is configured and operating correctly.


                By saying "... if all is configured and operating correctly", much is taken for granted.  Audio in PC's can be a tricky thing, it takes some knowledge in both the audio and PC world to get it working correctly.  It's one of the few areas in PCs where "plug and play" is not a given.

                • 5. Re: Why is the output from coaxial digital not 5.1?

                  http://http://en.wikipedia.org/wiki/S/PDIF   I beg to differ according to Wiki , S/PDIF is two channel , Unless you decode it into another format.

                  • 6. Re: Why is the output from coaxial digital not 5.1?

                    Mr. Gifford, you're missing my point, which is what is actually stated in the SPDIF article you referenced.  This is a statement from the Wiki article on SPDIF:


                    A common use for the S/PDIF interface is to carry compressed digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a home-theater receiver that supports Dolby Digital or DTS surround sound.  Another common use is to carry two channels of uncompressed digital  audio from a CD player to a receiver. This specification also allows for  the coupling of personal computer digital sound (if equipped) via  optical or coax to Dolby or DTS capable receivers. This only supports  stereo sound, unless the personal computer supports a surround sound  encoding such as Dolby Digital Live or DTS Connect


                    This is the Wiki article on Dolby Digital:




                    The soundtrack on a DVD with a movie will contain both a stereo only soundtrack to be compatible with equipment lacking Dolby Digital decoding, and a Dolby Digital 5.1 soundtrack for equipment that has DD decoding.  That is what is, very poorly, described in the last sentence of the paragraph from the SPDIF article.  Notice in the second and third sentences in that paragraph the description of two modes or uses for the SPDIF interface.  They are two different and independent uses of the SPDIF interface, which I mentioned in my earlier post.


                    If you check the article on Dolby Digital, you'll find the description of how the 5.1 (6) channels of audio are digitally encoded and transferred in the DD data stream.  If the SPDIF data stream is "always two channel", what is the point of all that encoded data?


                    My point again is we do not get 5.1 surround sound from two channel stereo with Dolby Digital, it is not derived from it via processing, but is part of the data.


                    But an important point that you may be alluding to is that the signal at the SPDIF output of a PC is not necessarily or automatically a Dolby Digital data stream, and in many cases will be simply two channel audio.  The hardware and software in the PC, from the DVD drive to the audio processing system to the OS must support Dolby Digital or it won't be available.


                    So let's make Mr. Gifford's statement a bit more rigorous for it to be absolutely correct.  Thus, the output of the SPDIF interface will always be two channel audio if the hardware and software in the signal chain does not support Dolby Digital 5.1 data retrieval.  Please note I am not saying that 5.1 surround sound is derived from two channel audio, it is not, but the hardware involved must be capable of receiving the Dolby Digital 5.1 data stream from a source that contains it, in order for it to be sent via the SPDIF interface for decoding.


                    Which again brings up this point.  If all Dolby Digital 5.1 processing does is take a two channel audio data stream and create the 5.1 audio channels, what is the point of everything described in the Wiki article on Dolby Digital 5.1 surround sound?


                    The original poster' said he had DD 5.1 when using Vista, but not when using Windows 7.  Are you saying that he is mistaken in the case of Vista, and there was no difference between Vista and Windows 7, and only had two channel audio in both cases?

                    • 7. Re: Why is the output from coaxial digital not 5.1?

                      Wikipedia strikes again I'm afraid (or more precisely the order details are listed - I've run into such problems myself in the past). In reality TOSLINK (optical S/PDIF) connections are normally used on modern consumer audio devices for multi-channel compressed audio far more than just regular PCM 2 channel transmission. Parsec wrote what'd almost qualify as a thesis here a few months back in response to a similar question - here's a link to the thread: SPDIF Audio Problems


                      Maybe the O/P will find that helpful to have a look at as well.

                      • 8. Re: Why is the output from coaxial digital not 5.1?

                        What I am saying UNLESS his mother Board has built-in decoding capabilities , it's going to be two channel sound coming out the S/PDIF and or the coaxial , I am not sure about the 975 board but I doubt if it has a built - in decoder.

                        • 9. Re: Why is the output from coaxial digital not 5.1?

                          Robert is correct in that upsampling and downsampling are going to be involved in some situations.  Stereo would preferably not be retained when using multiple channels.  Some of the problems encountered may involve sampling distribution and the clock used for Toslink optical connections.  Other problems are more concerned with video and copyright protection.  I suspect some of my recording problems involve copyright protection where garbage collection has not yet removed a hard drive copy of the buffered content present before actual recording was initiated.  Only after the issue is resolved by removing one permitted copy can the system become functional as before.

                          • 10. Re: Why is the output from coaxial digital not 5.1?

                            If you are having problems with copy right material , Check-out  SLYSOFT Just google it. But I did not tell you about it's UK .

                            • 11. Re: Why is the output from coaxial digital not 5.1?

                              I don't want any extra software, I just need to learn how to avoid problems, particularly BSOD.

                              • 12. Re: Why is the output from coaxial digital not 5.1?

                                What operations are giving you BSODs ??

                                • 13. Re: Why is the output from coaxial digital not 5.1?

                                  I only started to document exactly what gives BSOD but last time it was with TV tuner.  Determined what channel to record by starting the Live view.  Think I stopped that then recorded from there.  Shut down at end with no sleep or hibernation involved.  Next day start was unusually fast then restarted with BSOD.  Shouldn't really be a hardware problem but is interpreted as such.

                                  • 14. Re: Why is the output from coaxial digital not 5.1?

                                    Without even recording, the more likely explanation has surfaced again.  With the splitter and connections in use, the reliability of coaxial cable for TV can be erratic.  The signal can be disrupted long enough to interfere with startup, sleep and hibernation.  Boosters can be used for signals but I'll try reconfiguring the system.  It's probably best not to have a TV connected even to a splitter.

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