Sync compatibility in Monitors with FreeSync

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  • #26794
    RodrigoHC13
    Participant

    Hey, guys! New OSSC owner here. My package is on the way to my house!

    I have some doubts before purchasing a new TV/monitor to use with the OSSC and my consoles: SNES, Saturn, N64 (modded), PS2 and Wii. I’ve reading much of the content on the forum about the compatibility problems that some TVs have with unusual refresh rates (notably on SNES, because of the “sync jitter”) and about the 240p<->480i transitions.

    Note that buying a CRT/PVM is not an option for me where I live now.

    Here are my questions:

    1. If I buy a monitor with FreeSync technology instead of a TV, is there chances of increase the compatibility (or maybe eliminate this issues) with unusual refresh rates, like on SNES?

    2. Could also a monitor with this FreeSync technology successfuly reestablish the image after the 240p<->480i transitions without interrupting the video for a few seconds?

    3. Some monitors with FreeSync have HDMI and “Display Port” connections, and one of the manuals say that FreeSync is only available by connecting to the Display Port. Does this makes sense? The FreeSync could be only accessible via the Display Port and not via the HDMI?

    Thank you for the content on this forum!!

    #26797
    nmalinoski
    Participant

    1. I am not an expert, but it might improve compatibility to some degree, in that it may be more forgiving with refresh rates that are far off of an even 50/60Hz, but I don’t see any reason that it would provide any compatibility with the jittery sync we see with the NES and SNES.

    2. No. The TX chip in the OSSC conforms to HDMI 1.4, and it will blackout like it does with every other HDMI device/display. The only way you might survive mode switching with no lag is if the OSSC could gain compatibility with HDMI 2.1’s QMS, and only if you applied line2x or line4x to both 240p and 480i, which is not going to be ideal due to the bob deinterlacing.

    The alternative would be an FPGA video processor, not unlike the UltraHDMI, that can be configured to perform framerate conversion and scaling to continually output at a preset resolution and framerate.

    3. Looks like FreeSync over HDMI was implemented back in 2015, but using a vendor extension to HDMI, so you would need specific support for it on both the OSSC and your display.

    #26803
    RodrigoHC13
    Participant

    All right! I’ll be referring to the questions in a different order now:

    3. Understood now. Then a Freesync monitor needs a equipment designed to work with it. But I still have doubts if a Freesync monitor (even receiving signal from a device that wasn’t designed to work with the Freesync technology, like the OSSC), if compared to a regular monitor without this technology, will be equally or higher tolerant when dealing with fixed but unusual refresh rates.

    And considering this information:

    1. Can I conclude that the compatibility with unusual refresh rates isn’t improved by the Freesync, but by the “more forgiving with refresh rates” characteristic that many monitors have?

    2. Right, now I understood that during the 240p<->480i transitions the OSSC will blackout for a short period of time. Let’s not consider possibilities of changing the HDMI port, only considering what is possible with the v1.6 and accepting the OSSC inherent “blackout time”. Assuming that the recovery time from this “blackout” varies on different TVs/monitors, would this resync time be better on models with Freesync, even in a device that isn’t designed to work with this technology, like the OSSC? Or this is not what determines the better resync times on these monitors?

    Thanks!

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