Dolby Pro-Logic Encoder

Discussion in '3-D Audio' started by xzero1, Jul 12, 2005.

  1. Remboooo

    Remboooo New Member

    Nov 23, 2004
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    I've been using this plugin now and indeed it seems to work! There's one thing i don't understand though.. The wikipedia article about Dolby Pro Logic says that it adds the surround channel with phase shifting, but the only thing this plugin does is add the center channel to both left and right channels, substract the surround channel from the left channel and add it to the right.
    Could anyone tell me why substracting the surround channel from the signal is the same as phase-shifting it +90° and adding it is the same as phase-shifting it -90°? Or is this just a dirty hack that will work quite well, but not optimal?

    ah, I get it now. In stead of rotating one left 90° and the other right 90°, you just leave one untouched and negate the other one to approximate 180° rotation. Somehow in my setup the abovementioned 8kHz filter wasn't necessary and only (obviously) decreased sound quality from the rear channel.

    The code I now use in the dolby encoder component:
    input L, R, Ls, Rs, C;
    output Lout, Rout;
    static theconstant=0.7071;
    temp tL, tR, tS
    ; Code
    macs tL, L, C, theconstant; add center channel to left channel
    macs tR, R, C, theconstant; add center channel to right channel
    macs tS, Ls, Rs, 0x7fffffff; combine Ls & Rs to one temporary surround channel
    macsn Lout, tL, tS, theconstant; add 180° rotated (negated) surround to left channel
    macs Rout, tR, tS, theconstant; add untouched surround to right channel
    And before inputting the surround channels into the dolby encoder component, i make use of the TimeBalanceV2 component to add some delays to eliminate interference when the same audio plays on all channels. The settings that I use and seem to work fine (although they've just been established by trial and error - no science going on here):
    Front Left: 1.010m
    Front Right: 0.990m
    Rear Left: 0.808m
    Rear Right: 0.808m
    Center: 1.000m
    Last edited: Mar 29, 2007
  2. bobo1on1

    bobo1on1 New Member

    Oct 13, 2003
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    A dolby pro logic decoder has an 8 kHz lowpass for the rear speakers, sounds above 8 kHz in the rear channels will come out of the front speakers.

    ROBSCIX New Member

    Mar 28, 2004
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    A person was asking for a 5.1 encoder aswell, doesn't Trils redocneKX plug do this exact feature?

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