Mega Drive vertical trembling

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  • March 10, 2018 at 10:22 PM #19987
    Helio2000
    Participant

      Hi,
      I have a set up involving a PAL Mega Drive I + Mega CD II + Sega 32x, a 32x packapunch cable from retrogaming cables and an OSSC.

      The image quality is astonishing un general but there is always a vertical area suffering from slight pixel trembling. This area represents about 1/8 of the screen.

      I have changed several parameters so far including Sync options such as LPF, phase… but I only seem to be able to move this trembling area horizontally.

      Has anyone seen something similar and has solved It?

      March 11, 2018 at 2:57 PM #19996
      nmalinoski
      Participant

        Does this trembling happen when connected directly to your TV (via composite or whatever)?

        March 12, 2018 at 8:39 PM #20025
        Helio2000
        Participant

          Hi. When connecting the SCART cable to my monitor directly there is no such trembling. Everything seems fine.

          March 13, 2018 at 7:41 PM #20059
          BuckoA51
          Keymaster

            Does your MD have a 60hz mod?

            March 13, 2018 at 8:47 PM #20060
            Helio2000
            Participant

              No, it has not been modified.

              I can tell you that my PAL PS1 does not have the trembling though.

              Thanks.

              March 14, 2018 at 10:21 PM #20102
              Helio2000
              Participant

                I have been doing some tests and it looks like the trembling only happens when I enable the line 2x 320×240 optim, 256×240 optim and line 3x optim modes.

                If I set just generic 16:9/4:3 modes the trembling goes away.

                Is this something expected?

                March 15, 2018 at 8:40 AM #20109
                Harrumph
                Participant

                  Yes. Optimized mode requires exact sampling rate of console dot clock output, otherwise you will get exactly those types of fuzzy or trembling columns.

                  Iirc, the default samplerate for 320×240 optimized is 426, but MD is more like 427 or 428. Adjust that and you should see an improvement.
                  (obviously, if it’s a 256 horizontal game, you need to use the 256×240 mode instead, I believe FirebrandX made a list at some point which may be googleable.

                  Additionally, optimized modes usually requires some adjustment to sample phase, which is under Sampling Options.

                  http://junkerhq.net/xrgb/index.php?title=Optimal_timings

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