Digital signal

Discussion in 'Archived Threads 2001-2004' started by Sacha_C, Jan 14, 2003.

  1. Sacha_C

    Sacha_C Second Unit

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    Is the digital output on Sound blaster audigy cards compatible with Coaxial digital inputs on receivers or is it a different type of signal?

    If it is compatible, does it carry all 6 channels of 5.1 surround? If not what is the best way to connect a PC to a receiver to get 5.1 audio for DVDs?

    Thanks
     
  2. Andrew Pierce

    Andrew Pierce Stunt Coordinator

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    On the Sound Blaster Audigy, one of the small stereo headphone-style jacks can be set to output digital audio. You need an adapter to convert from the mini-headphone style (mini-din?) to a pair of RCA coaxial style femaile connectors. One of those two connectors carries the front left/right signal and the other carries the rear left/right signal. The good news is that the front left/right can be set to output a 96/16 signal. The bad news is that no stereo I know of will decode a signal sent out on two seperate coax lines, so sending out the rear signal like that is, quite frankly, retarded. I really don't understand how Creative Labs justifies selling their sound cards for the prices they do, except that they ran almost everyone else out of the market. I suppose you could hook up one receiver to decode the front and the other to decode the rear. Whatever. My advice is to take what you can get -- a pretty good quality steroe digital signal, or feed the receiver an analog signal via a 5.1 input.

    Or, better still, junk the Audigy crap and get an nForce motherboard which has does hardware 5.1 dolby digital encoding out your choice of optical or coaxial outputs (of course, depending on the model) The ASUS A7N66-VM (I believe that's the model) is a micro-ATX nForce 1 motherboard and can be had for around $70 online and comes with both optical and coaxial of output, fits in a smaller HTPC friendly case, includes onboard video and LAN, takes an AMD athlon up to 2600 (or higher if you can find 'em). Sound quality is excellent, DD encoding really works, or you can just stream 48/16 (which is likely good enough since you're likely going to be streaming MP3s, DIVX, Internet radio or some other compressed source from your HTPC.
     
  3. MichaelTa

    MichaelTa Agent

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    If you have a live drive you can do coax out to coax in on the receiver. The live drive's show it as spdif out. I use this to play streaming audio on my home system. I use the spdif in to record music to my hard drive from my stereo as well.
     
  4. Sacha_C

    Sacha_C Second Unit

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    Doesn't SPDIF carry only stereo audio and not 5.1?

    Thanks
     
  5. Brian_Tho

    Brian_Tho Stunt Coordinator

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    Spdif can carry 5.1 its the same as the digital out on the back of your dvd player.
     
  6. Sacha_C

    Sacha_C Second Unit

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    Is SPDIF and Coaxial digital the same thing?

    Thanks
     
  7. Brian_Tho

    Brian_Tho Stunt Coordinator

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    Yes. Sony Phillips Digital Interface. We need a chat room on this board!
     
  8. Andrew Pierce

    Andrew Pierce Stunt Coordinator

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    Audigy's S/PDIF can cary a 5.1/6.1 signal from a DVD only, as a passthrough device. It can only cary a stereo signal for non-preencoded material. And the livedrive adds an optical toslink connector, but the coaxial S/PDIF on it is the same as what you get out the orange plug on the back of the card. The livedrive is WAY, WAY overpriced for what you get.
     
  9. AaronBatiuk

    AaronBatiuk Second Unit

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    Okay,
    S/PDIF (Sony/Philips Digital Interface) carries digital audio. It can carry both PCM and non-PCM audio. If you have a digital output on the back of your CD player, that is PCM audio. It is uncompressed 44.1 kHz sampling rate, 16 bit samples (44/16 for short) in stereo (2 channels). PCM can be of almost any bit depth and sampling rate, but S/PDIF has a limit on it's bandwith, so stereo 192/24 (the high resolution DVD-Audio format) is out of the question. Stereo 96/24 will work though. S/PDIF can carry up to four channels of PCM audio. No source that I know of (including soundcards) transmits four channels on one S/PDIF link, and no receiver that i know of will decode four either. In the real world, S/PDIF almost exclusively carries stereo PCM, or non-PCM signals.
    Non-PCM can include Dolby Digital, dts, or MPEG signals. These are not raw samples like PCM, but a compressed bitstream that the receiving device must decode into raw samples before being converted into analog audio.
    S/PDIF can be transmitted in one of three ways:
    1. Over optical cable using Toshiba's TOSLINK connector technology using red light at ~650 nm.
    2. Over coaxial cable with a characteristic impedance of 75 ohms and at least 9 MHz of bandwidth (video cable is perfect for this), at 0.7 Vp-p, or
    3. Twisted pair at TTL (0 to 5 V) levels.
    The soundblaster cards use option 3, and transmit stereo audio (48/16 for Live! cards and up to 96/16 for Audigy). Strictly speaking, the voltage being transmitted is not compatible with option 2, but it usually works anyway. To use it, buy at Stereo (not mono) to 2 RCA jacks adapter, like this one from radio shack. Plug it into the soundcard's digital output (on some models, you need to configure one output to be digital) and connect one of the RCA jacks to a digital input on your receiver using a good quality video cable. One of the RCA jacks is the front two channels, the other the rear two. You'll have to try both; I can't remember which is which. You will get the computer's sound in stereo (including games and such), and audio from DVD can be output directly (i.e. DD or dts bitstream) for your receiver to decode.
     
  10. Andrew Pierce

    Andrew Pierce Stunt Coordinator

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    Awesome post, Aaron! Great info! So in all likelyhood, the live drive actually does get you a 'true' coaxial connector, as opposed to what I am using on my HTPC, which according to you info must be a 'TTL level' coaxial out the back of the Audigy sound card.

    In any case, I'll likely upgrade my main PC to a nForce2 board next month, migrate my nForce 1 board to the HTPC and then I'll be able to get DD 5.1 encoding in my HTPC, or 48/16 PCM. I just wish the nForce boards allowed 96/16 like the Audigy or 96/24 like the Audigy 2, but it shouldn't matter too much, since, like I said, most non-DVD sources rolling out my HTPC going to be from a compressed source with sub-48/16 quality anyway.
     
  11. Sacha_C

    Sacha_C Second Unit

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    I just realized my video card has an SPDIF output (for DVD audio only).

    Anyway, if I get an audigy later, can the DD/DTS signal still be output if you use a splitter and conenct only 1 of the 2 ends to the recevier?

    Thanks
     
  12. Brian_Tho

    Brian_Tho Stunt Coordinator

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    Why do you need a splitter? Just get a rca to 1/8 jack adapter put on your coax connect to the audigy stream anything from music to dvd audio stream to your receiver. H
     
  13. Andrew Pierce

    Andrew Pierce Stunt Coordinator

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    The splitter is the split the stereo mini-jack to 2 mono mini-jacks (one front and one rear), which you can then adapt to RCA.

    I'm almost certain that you can use the front L/R to pass DD/DTS, but I can't currently test that as I don't have a DVD drive in the box with the Audigy right now, only in my main PC.
     
  14. Brian_Tho

    Brian_Tho Stunt Coordinator

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    Right know I am listening to music from my audigy to receiver coax with mono adapter rca to 1/8jack. I can stream dts,dd,music
     

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