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Thread: Decimator MD-LX computer HDMI to SDI

  1. #1
    Registered User DStoneburner's Avatar
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    Decimator MD-LX computer HDMI to SDI

    So having a little issue sending a computer through a Decimator MD-LX into the TC8000. I have a 1080i show and the only way the SDI would see the computer is if I dropped the refresh rate down to 29 htz. I usually run computers at 60. Just wondering if anybody else has used an MD-LX with the TC. We have the larger MD-HX, which works well but bought a couple of the LX because of the price. Thanks

  2. #2
    Registered User Stream's Avatar
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    Tricaster 460 Advanced Edition 2, Tricaster 40 V1
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    There are two kinds of HDMI. Video HDMI and computer HDMI.
    They work with different resolutions and different refresh rates.
    If you have a video HDMI (coming out of a camera, or other professional video source), then using the Decimator or the Blackmagic converter to convert to SDI should be fine.
    But if you're trying to get a computer HDMI source into a SDI production environment, you really should use a scan converter and not a HDMI to SDI converter.
    The scan converter is better equipped to deal with computer-specific HDMI sources, and convert them properly to SDI.

    For scan conversion, we use: Gefen HDMI/VGA to 3G-SDI Scaler/Converter B&H # GEXHDVGA3GSC MFR # EXT-HDVGA-3G-SC

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    We use the NDI Scan Converter to pull-in multiple PC's into our TC8000. Have you tried that?

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    We use the ndi or datavideo dac-70

  6. #6
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    You need to look at the TC8000 specs;
    Local Video Input
    8 x local video inputs supporting any combination of compatible connections (SDI, Component, Y/C, and Composite), formats, resolutions, and frame rates
    1080p: 29.97, 25, 24, 23.976
    1080i: 59.94, 50
    720p: 59.94, 50, 29.97, 25, 24, 23.976
    576i 25
    480i 59.94

    Specifically, you need to consider that there's a difference between P (progressive) and I (interlaced). At 60fps progressive you're getting 60 full-height frames each second. At 60fps interlaced you're getting 60 half-height (ie; every second line of the picture) frames every second. Therefore, the data rate required to do so is quite different. Your TC8000 only does 60fps interlaced, not 60fps progressive. So you have options;
    - Run the PC at ~30hz (fps) progressive (which works as you've found).
    - Run the PC at 60hz interlaced (which also works, but is only supported by some PCs).
    - Run at 60hz into something like a Decimator MD-HX which can do conversion from P to I for you.

    This is because the SDI inputs on your Tricaster support rates up to SMPTE 292M (https://en.wikipedia.org/wiki/SMPTE_292M). To be able to do 60P you'd need the Tricaster inputs to either support SMPTE 372M (dual-link SDI which uses two SDI lines in tandem to support the data rate), or the newer SMPTE 424M (commonly known as 3G-SDI).

  7. #7
    Registered User DStoneburner's Avatar
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    I've had nothing but issues with BM converters in the past. I prefer the AJA but wanted to give the small inexpensive Decimators a try. Thanks for the suggestion. I figured out how to make it work, just like you suggested, I was able to change the refresh rate to 30 interlaced or 29 depending on the computer. It worked well. I usually use the HX, which converts, but I bought a couple of MXs just in case. I can't always use NDI because currently I'm in discussion wth our IT about having more than 2 devices on a swtich when plugged into the network for streaming. Thanks for the quick replys.
    Last edited by DStoneburner; 04-30-2019 at 06:17 AM.

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