projector sync and freq HELP?

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  • Brandon B
    Super Senior Member
    • Jun 2001
    • 2193

    projector sync and freq HELP?

    This is a question for those of you experienced with HTPCs.

    As some of you are probably aware, the Bravo D1 has new firmware avaliable which allows setting up a custom output resolution to match your PJ, useful for those who's displays don't match an industry standard TV def. Mine is 1366 x 768.

    I began by inputting a set of values someone was using in powerstrip for the same PJ I have in an HTPC, I believe in Powerstrip. While he had these values working with he PJ (Sanyo PLV70), as posted they did not work with the D1 (screen was scrambled). Horizontal frequency was 56.159, and all other values listed below were as shown.

    I played around with several of the parameter. I understand the function of several of them at a basic level, but not nwell and do not understand what effect altering most of them will show in the image. I finally got an image with the settings below. The image appears for values of HFreq from 44 up to about 53-54. I am running it as show below.

    Hfreq - 52060
    Vfreq - 72020
    Horiz res - 1366
    Vert res - 768
    HSync total - 1784
    PreHSync - 80
    HSyncActive - 136
    PostHSync - 208
    VSync total - 780
    PreVSync - 01
    VSyncActive - 2
    PostVSync - 10
    HSync Polarity - +1
    VSync Polarity - +1

    First thing, it seems odd the PJ would reject the same signal it accepts from an HTPC unless A) differences in individual PJs or B) D1 generates signal with dfferences from HTPC, even with same parameters set.

    Any way, now to my problem and question. In comparing the picture at 1366x768 vs. the D1's standard 720p and 1080i output options I see the following:

    On custom, pans across vertically lined images seem to jerk a little. Likewise, while watching TTT, there seems to be a fairly slight jerkiness to CGI generated images, almost giving them an appearance of old stop motion. On the other settings, this does not occur.

    Plainly, one of my parameters above is set less than optimally. Since while the image detail is as good or better at my PJs native rez, this is really distracting and I prefer using another setting even with the dual scaling going on.

    So can one of you help with one or more of the following:

    Point me in a good direction to get specifics on the function and effect of the above parameters on a video image;

    Let me know which of the above parameters might be adjusted to minimize the effect describe;

    Let me know if any of the values above seem out of whack based on your experience.

    Thanks!

    BB
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15282

    #2
    Hello Brandon,

    You know, I don't know how anyone would get really smooth DVD playback with the refresh rate which the 12T and Sanyo's require for 1:1 pixel mapping, due to their scaler chip set. This may be a problem.

    Normally, what' I'd do is scope the signals to compare how the PC and the D1 are handling the timing parameters. But that the other side of the equation is how the MPEG decoder is assembling frames for the frame rate of playback. Are you testing with film sourced material? It's hard to make 24 FPS wind up in 56 or 54 cleanly... it may be that the frame dropping or skipping on the PC works better, I don't know.



    Best regards,

    Jon




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    • Brandon B
      Super Senior Member
      • Jun 2001
      • 2193

      #3
      Material was TTT. Also saw the same bevavior on AOTC disk, which while not film based, is equivalent I guess (24 fps).

      What I don't get is it is greatly reduced using the 720p setting on the D1, which is being scaled by the D1 AND the Sanyo. I suppose it is possible that the slight loss of detail is making the movement of things a little blurrier and therefore more natural looking, but I don't think so.

      I'll compare the two again tonight. Don't have a scope myself.

      BB

      Comment

      • Brandon B
        Super Senior Member
        • Jun 2001
        • 2193

        #4
        Image also worked set at 48 Hfreq. I'll try that too, since it is a nice multiple of 24.

        BB

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        • Brandon B
          Super Senior Member
          • Jun 2001
          • 2193

          #5
          Another member with the same setup posted this over at AVS:

          I have done some research and tweaking and found the reason for the frams stuttering. The Hfreq must be equal to the Vfreq times the # of scan lines. After referring to the PLV70 service and user manuals I found that the recommended refresh rates for a 768 line display is hfreq: 48.363 kHZ and vfreq: 60.004 Hz, doing the math yields a total of 802 horizontal lines. Using these modifications to the frequencies and the Vsync total gives smooth video with no stutter. I also played with higher refresh rates and I am now using the following settings:

          Hfreq - 60150
          Vfreq - 75000
          Horiz res - 1366
          Vert res - 768
          HSync total - 1784
          PreHSync - 80
          HSyncActive - 136
          PostHSync - 208
          VSync total - 802
          PreVSync - 01
          VSyncActive - 2
          PostVSync - 10
          HSync Polarity - 1
          VSync Polarity - 1

          The limit of the pj's 140 Mhz dot clock would imply that we coud go up to a horizontal refresh of 100kHz, but I have not tested it.

          Geometries all check out at 1366x768 although the image is slightly (VERY slightly) sharper at 1364x768 which is the default for the Gakaku Pixcel Works default in the PLV 70. ( I know, its all greek to me too, but that is what is delineated in the service manual.)


          I'll try his values tonight.

          BB

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