DVDFab Forum - Dolby Pro Logic II Down-mixing is incorrectly implemented!!!


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Dolby Pro Logic II Down-mixing is incorrectly implemented!!!

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  • Dolby Pro Logic II Down-mixing is incorrectly implemented!!!


    I'm a new user. I just downloaded and started a trial version of DVDfab. I'm used to the open source software Handbrake and decided to give DVDfab a try because it can use CUDA for processing.

    Although video encoding works fast and great, I discovered a serious bug when down-mixing a video with discrete 5.1 to 2.0 audio with matrix surround encoding. Unlike Handbrake's DPLII mixing, which is implemented correctly, DVDfab's DPL2 mixing is actually a simple stereo mixing!

    This is a sample test video - the original video with DTS-MA 5.1 soundtrack:


    This is the same video with 2.0 downmix handled correctly by Handbrake:


    Now, this is the same video again with 2.0 downmix handeled by DVDfab (sellecting DPL2 option and AAC audio):


    Please try to play and compare results while you AV receiver surround mode is set to Dolby Prologic 2 (or Dsur, or DTS Neo 6, or DTS Neural X).

    You will notice the following:

    In the handbrake result, left and right surround test tones are heard from the corresponding left and right surround speakers, while in the DVDfab result, they are heard only from the left and right FRONT speakers!!! This is a major bug and very disappointing, coming from a commercial software.

    Here is the problem: To correctly down-mix 5.1 channels, the channels must be matrix-encoded into 2 channels, called Left Total (LT) and Right Total (RT). Suppose you have 5.1 channels of Front Left (FL), Front Right (FR), Center (C), Left Surround (LS), Right Surround (RS) and LFE (S), then this should be the correct DPL2 encoding:

    For LT:

    LT = 1.0*FL + 0.0*FR + 0.707*C + 1.0*LS + (-0.5)*RS

    For RT:

    LT = 1.0*FR + 0.0*FL + 0.707*C + 1.0*RS + (-0.5)*LS

    The above will result in correct steering when played back using any matrix based surround decoder like Dsur or DTS Neural.

    DVDfab incorrectly merges the two surround channels to the total front channels. This is the incorrect algorithm of DVDfab according to my analysis using Adobe Audition:

    For LT:

    LT = 1.0*FL + 0.0*FR + 0.5*C + 1.0*LS + 0.0*RS

    For RT:

    LT = 1.0*FR + 0.0*FL + 0.5*C + 1.0*RS + 0.0*LS

    Can someone bring this to the developers attention? If this gets fixed in the next release, I'll definitely buy the full version of DVDfab.


  • #2
    Thanks for your feedback, I am not sure anyone else has ever reported this. The developers will check it ASAP.
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    • #3
      Just updating: I also tried DTS-MA 7.1 to 2.0 using DPL2 mode in DVDfab and here, the situation is even worse, as both Surround Back channels (LB and RB) are completely lost (discarded).

      This should be the correct algorithm for 7.1 to 2.0 downmixing:

      For LT:

      LT = 1.0*FL + 0.0*FR + 0.707*C + 1.0*LS + (-0.5)*RS + 1.0*LB + (-0.707)*RB

      For RT:

      RT = 1.0*FR + 0.0*FL + 0.707*C + 1.0*RS + (-0.5)*LS + 1.0*RB + (-0.707)*LB



      • #4
        Hi EB1000,

        Please update to Beta version to have a try.

        DVDFab log default location:
        For Windows: C:\Users\User Name\Documents\DVDFab11\Log
        For Mac: Finder>Documents>DVDFab11>Log

        DVDFab Player 5:
        For Windows: C:\Users\User Name\Documents\DVDFab Player 5\Log
        For Mac: Finder>Documents>DVDFab Player 5>Log

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        --Please use attachment button to attach your most recent log files.