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  1. Is there a way to decode an AC3 2.0 Surround file into separate elements? DVD Audio Extractor extracts three streams, but one of them is silent. If my amp does it to playback sound, can a software program do it too?

    I doubt its possible given my knowledge of audio but thought it might be worth a shot.
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  2. Originally Posted by GavSalkeld View Post
    Is there a way to decode an AC3 2.0 Surround file into separate elements? DVD Audio Extractor extracts three streams, but one of them is silent. If my amp does it to playback sound, can a software program do it too?

    I doubt its possible given my knowledge of audio but thought it might be worth a shot.
    I'm not exactly sure what you're asking by "separate elements" ?

    Do you mean separate Left + Right channels? If so , you could convert them to mono wavs e.g. in eac3to, or audacity
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  3. Sorry, I meant is there a way to extract the surround information and front channels into separate mono files.
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    well AC3 2.0 doesn't have surround information..just left and right channels. That would explain why only 2 extracted channels have sound.

    ac3tool will extract all the channels to mono .wav files.
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  5. I think he means Dolby Pro Logic , and it does include "psuedo" surround information in the 2.0 configuration (when engineered, its mixed from 5-channels)

    AFAIK there is no way.
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  6. Pro Logic is the name of the technology, the hardware that decodes it. Dolby Surround is the name given to the audio encoding method. But yes, that is what I mean!
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    doesn't ffdshow have a Prologic decoder ???
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  8. I dont know, Ive heard of it but Ive never used it.
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    Yes, it has, and yes, it "upmixes" stereo into 5.1.
    Not sure if it does the job correctly, though.

    First, you'd have to produce a 6-channel .WAV from the 2.0 AC3 source,
    then convert the multichannel .WAV to 6 mono .WAVs.
    I would use Graphedit + File Writer,
    or Graphedit --> .GRF file --> Avisynth + SoundOut.
    Next step, either eac3to or tranzcode.
    Last edited by El Heggunte; 12th Jul 2010 at 18:20. Reason: typo
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  10. Forgive my newbieness, but where does ffdshow come into this? Can't I just open the AC3 in there and do the AC3 to WAV in there?

    And surely it wouldnt be a 2.0 to 6-channel WAV, it would be a 4-channel WAV right? Left, Center, Right, Surround (mono)?

    Thanks so much.
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  11. You can build a graph to do it with GraphStudio and ffdshow's audio decoder.

    Click image for larger version

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    Enable ffdshow's Dolby decoder.
    Last edited by jagabo; 17th Jul 2010 at 12:20.
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  12. Ive never used either of those, can you tell me briefly how to do it? Say I have the AC3 file saved, what do I need to do first?

    And this will demux a 2.0 surround AC3 to a multichannel WAV?

    Thanks for your help, really.
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  13. Member Cornucopia's Avatar
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    Search the threads - There is an audio DirectX plugin that allows de-matrixing of Lt+Rt (that's the nomenclature for Dolby Surround/ProLogic encoded result files) back into L+C+R+S. Can't remember the name (although I'm sure I DL'd it at one point).

    Note: since Dolby Surround/ProLogic/PLII matrixed files are matrixed, they ARE 2-channel files. In every occurence. So you should be starting with a stereo WAV, or 2ch MP2 or AC3 2.0 file, etc.

    BTW, Dolby "Surround" decoders decode to 3 or 4 channels and with bad crosstalk. "ProLogic" decoders decode to 4 channels with much less crosstalk (but it still is apparent). "ProLogic II" decoders decode to 5 channels, with even less crosstalk, but they have to have been encoded correctly using "PL2" encoding matrix which has been modified from the standard "Surround/PL" encoding matrix. Using PL-encoding with PL2 decoder is usually ok, but using PL2-encoding with a PL decoder can get a little weird sounding.

    Scott
    Last edited by Cornucopia; 17th Jul 2010 at 13:35. Reason: typo
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  14. Do you know the name of the DirectX plugin? What program do I use it with?
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  15. Originally Posted by GavSalkeld View Post
    And this will demux a 2.0 surround AC3 to a multichannel WAV?
    Yes.

    Originally Posted by GavSalkeld View Post
    Ive never used either of those, can you tell me briefly how to do it? Say I have the AC3 file saved, what do I need to do first?
    You can find some basic GraphEdit (GraphStudio is a third party clone with more features) guide with a google search. Here's one example:

    http://www.3ivx.com/support/windows/encoding/ge_avi2mp4.html

    Install GraphStudio (or GraphEdit) and ffdshow. Make ffdshow your default AC3 decoder. Then drag your AC3 file onto the GraphStudio window. It will automatically build a graph to play the file. You don't want to play the file so delete the audio renderer at the far right. The last filter in the graph should now be Ffdshow Audio Decoder. Right click on it and select Properties. In the Propreties dialog turn on the Dolby Decoder. In the Mixer section set the Output Speaker Configuration to 3/0/1 Surround. Close the dialog. Back at the main window select Graph -> Insert Filter... I added WAV Dest (builds WAV file format, comes with GraphEdit9) and File Writer (writes the file). You may need to connect the two filters to the graph (drag from the output pin of one filter to the input pin on another). Then press the play button in the VCR controls section.
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  16. OK I will give this a try and report back to you. What kind of results can I expect to get, will it be pretty decent? Kind of a vague question, I know. Sorry.
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  17. You'll get pretty much whatever any matrix decoder would put out. Like Conrucopia said, it's not perfect, lots of crosstalk.
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  18. Crosstalk meaning bleeding frequencies from other channels?
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  19. Yes. You don't get 100 percent channel separation. The rear channel is low bandwidth too, about 7 KHz.
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  20. I looked into this a few years ago when I only had 5.1 computer speakers plugged straight into the back of my DVD player. There were a couple of free utils that would let you generate 6 wav files which you could then use to author a DVD with 6 discrete channels that would give me surround on my setup, but it wasn't very convincing. It was time consuming and after comparing the results on friends' surround systems I decided it was a lot easier just to get a surround sound system with pro-logic capabilities built in. As I said, this was a few years ago, so things may well have improved since then. Good luck and let us know how you get on.
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  21. Thanks everyone for your help and support. I will keep you posted!
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  22. Originally Posted by jagabo View Post
    Install GraphStudio (or GraphEdit) and ffdshow. Make ffdshow your default AC3 decoder. Then drag your AC3 file onto the GraphStudio window. It will automatically build a graph to play the file. You don't want to play the file so delete the audio renderer at the far right. The last filter in the graph should now be Ffdshow Audio Decoder. Right click on it and select Properties. In the Propreties dialog turn on the Dolby Decoder. In the Mixer section set the Output Speaker Configuration to 3/0/1 Surround. Close the dialog. Back at the main window select Graph -> Insert Filter... I added WAV Dest (builds WAV file format, comes with GraphEdit9) and File Writer (writes the file). You may need to connect the two filters to the graph (drag from the output pin of one filter to the input pin on another). Then press the play button in the VCR controls section.
    OK I finally had some time to check this out. This is what my window looks like:



    When I chose the file writer plugin, it asked for an output name so I just entered "r1.wav" in the dialog box. Is that right?
    Anyway I press Play but nothing seems to be happening. What should happen, will I get a 3-channel WAV file?
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  23. When you press the Play button it should turn gray and the Stop button should turn red. There is no other indication the program is working (except the output file is created and growing, if you look at it). When the buttons turn back to their original colors the conversion has completed.

    You should use the Browse button in the File Writer filter to make sure you know where the output file is created. Otherwise you may have to hunt for it.

    The WAV file will have whatever number of channels the source had or whatever number ffdshow was set to remap it to. You can examine any of the filters, input pins, or output pins by right clicking on it an selecting Properties.
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  24. Thanks again, that worked. Seriously; big thanks.
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  25. Glad it worked out for you.
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  26. Let me know if there is something I can do for you by way of thanks. Drop me a PM or something.
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  27. Hi,

    I am trying to do this now with a Laserdisc PCM stream that was captured to PC. It's a stereo stream that is labeled as Dolby Surround on the disc, so I think a Pro Logic de-matrixing would be perfect to extract 4 discrete channels out of it, and then make a new 5.1 mix based on that.

    I downloaded GraphStudio and ffdshow, but I can't seem to figure out how to make ffdshow the default decoder in GraphStudio. Any help would be greatly appreciated.

    Thanks!
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