Advanced timing settings for Amiga

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  • #16804
    jdryyz
    Participant

    Ok, I’ve been able to spend some more time with the OSSC and have decided it will be best used with my dedicated gaming Amiga. This is the PAL A1200 connected to a 60″ Vizio M60-C3. Screenmodes will be mostly PAL Hi Res, then PAL Hi Res Interlaced and some NTSC Hi Res. Nothing outside of the 15KHz domain.

    The OSSC has good default settings for the most part and I find that LineX2 is best for compatibility. The Vizio will not display LineX3 or X4 but will display X5 although it will take a lot of adjusting to reduce the overscan (if that is even possible).

    I was not able to display NTSC screens at all until I changed the HPLL pre&post coast to 3 as marqs recommended. So far, this is the only change from the defaults I have made.

    I have been enjoying an amazing retro feel with the high quality RGB output the OSSC delivers. Seeing all those demos and games on the big screen without any of the artifacts is very satisfying.

    There are a couple problems, though. 1) When switching from Hi Res to Hi Res Interlaced, OSSC will temporarily lose sync (video and audio drops out). This is nothing major with most software but if a demo, for example, were to switch frequently between these modes, it disrupts the flow. My TV could be to blame for this but I don’t know for certain. 2) A similar loss of sync happens but not due to a screenmode change. It appears to be completely random. I will just be in the middle of something and then *bam* the video and audio drop out for a moment. I think I read about others experiencing this with specific game consoles.

    I do not think I can do anything about #1 but I wonder if #2 might be something I can compensate for. I just do not know what setting is related to it.

    jarp, you do have advanced timing settings for PAL Hi Res but you also list LineX3 for these. Since I am only using LineX2, do I still need to tweak these settings? I am able to use full overscan with the defaults.

    #16814
    jarp
    Participant

    “jarp, you do have advanced timing settings for PAL Hi Res but you also list LineX3 for these. Since I am only using LineX2, do I still need to tweak these settings? I am able to use full overscan with the defaults.”

    Please ignore my all other posts, take a look of the opening message only, that has up to date timing settings. Everything else is just stream of thought. I wish I could delete all the other posts I’ve made, they are misleading.

    Use only LineX2 or LineX4 to get best results and tweak advanced settings to get perfect picture. With default settings you re throwing away full potential of the OSSC and could use any generic scan converter instead. This may not obvious with games, but use checkerboard pattern as WB background and you will see it.

    #16816
    jdryyz
    Participant

    Well I have to disagree somewhat with your statement about throwing away the full potential. The OSSC provides three very important improvements over generic scan converters (albeit I only one device I can compare it to): 1) Almost zero lag, 2) no blurry motion artifacts, and 3) scanlines.

    I made your recommended adv. timing changes for PAL Hi Res and used the Workbench checkerboard pattern to assist. You are right, I did see some improvement in the pixel image quality, most noticeable with characters “M” and “W” but the change was not that dramatic in my case and it came with a downside: The image is shifted too far to the right and is being cut-off. The setting responsible for this is H.samplerate. I can compensate 100% for this by adjusting the Workbench overscan preferences. Unfortunately, this will not help the default image position in games and demos.

    The next biggest setting that helped bring out a sharper picture was the sampling phase (especially noticeable with that checkerboard pattern).

    I suspect the variation in these settings being less than optimal will depend on the display type. The closer I get to the display’s native resolution, the more pixel-perfect it will be. My Vizio is 4k and 16:9. A 2k monitor at 16:10 will give different results I’m sure.

    The other settings did not make a visual difference at all, at least none that I could detect. But, something may have had an impact on the random loss of sync. I have not seen it happen since making the changes.

    I did have to return H.samplerate back to what it was. I was even thinking I could reduce it more and that could move the image more to the left. As you are probably aware, the Amiga screenmodes are shifted slightly to the right compared to default monitor settings back in the day. It appears to still hold true with modern displays.

    #16819
    jarp
    Participant

    Yeah seems some monitors behave differently than others when h.samplerate is adjusted. My new 4k monitor does the same, image shifts to the right. My old monitor did not. That’s a bummer.

    But I wonder… for me adjusting settings and not adjusting are like day and night, difference is insane (as expected if you think about it). From your wording (“native resolution”) I think you have scaling enabled in your monitor so your monitor always scaled the picture to full screen? Then it makes 100% sense that you won’t notice big differences; your monitor will ruin the result anyways.

    Try to disable scaling, how it behaves after that?

    Ps. It’s not only scaling per se which is the problem… it inheritently blurs the result. But it’s that some monitors have crappy scaling algorithms. Like my new cheap 4k monitor, it’s horrible, there is weird scaling artifacts etc. My old monitor had much nicer scaling algorithm and I did not mid using it. With my new… no.

    #16821
    jdryyz
    Participant

    Because I am working with a TV and not a computer monitor, I do not have the ability to disable scaling. I imagine there could be a consumer TV out there that might have such a setting but it is probably a high-end device. Actually, the 12 year old 37″ Sharp LCD TV I had *did* have a option to turn this off! Yes, it was a computer-friendly TV!

    The Vizio does have zoom modes and I am pretty certain I already have it set to something that supports 4:3. Anything else will just distort the image. I will double check this.

    #16824
    jarp
    Participant

    Ah makes sense I see… It’s pity TVs have such a limited amount of settings but understandably average viewer want’s full screen picture always. Oh well, in any case OSSC is great device, scaled or not…

    #16827
    jdryyz
    Participant

    Agreed. I am happy with it so far.

    Turns out that changing H.samplerate to something other than the default value of 864 stopped the momentary sync loss.

    Scratch that. It seemed to help for a while but did not last.

    Another thought I had was to swap my HDMI cable. I went from a cheapy 6ft cable to a better 3ft one. It seemed like it helped at first too but the random loss of sync continues to happen.

    #22795
    ilgello
    Participant

    Hi jdryyz are you still following this thread ?

    I think we have the same issue, bad news I still haven’t fixed it either, good news the other Amiga I have (both recapped) have a crystal clear and stable image with the OSSC.

    The problematic one is a A1200 1d4 board, what about yours ?

    #22796
    jdryyz
    Participant

    I’m still here!

    Interesting observation on the motherboard rev. I will have to open the case and take a look. Stay tuned…

    #22798
    jdryyz
    Participant

    1D.4

    Could be one of these A1200 “timing” issues perhaps? I am using an ACA accelerator in this machine also. No problems with any other software I’ve thrown at it so far with one exception…a demo that crashes. I think it just doesn’t like my accelerator for some reason, not the A1200.

    #23057
    bni
    Participant

    Hi, This is a report of my findings with the OSSC I got a few weeks ago:

    My Hardware:
    Amiga 500
    OSSC latest rev and firmware
    65″ LG C7 OLED TV

    Default settings gave me ok picture but hitchy/jumpy scrolling, and not pixel perfect. Hard to say if the jumpyness was caused by TV having trouble with scaling the default resolution or if it was from OSSC.

    After tweaking the settings the picture is jaw dropping if I may say so. Black is black, pixels are 1:1 mapped and scrolling is super smooth. The true blacks really bring out the graphics from Amiga demos and games.

    Its def. worth it to tweak the settings for the Amiga with OSSC.

    Im using the settings (sort of) from one of jarps posts in this thread:
    Line3x mode (Default 4:3 setting)
    H. samplerate 1818
    H. synclen 72
    H. backporch 198
    H. active 1440
    V. synclen 3
    V. backporch 24
    V. active 288

    This gives a 1280×855 resolution that the TV then scales to 2160p. I have no idea if these settings are optimal, I just used info from this thread and some experimentation. If anyone have suggestions how to improve Im very interested in that.

    Remaining issues:
    Settings captures the whole overscan area on the left side, and I guess that is interesting, but somewhat distracting in some demos.

    Aspect Ratio looks ok, but im not sure it is 100% accurate.

    I want to enable Line4x mode instead, but have not been able to find settings that looks good. Anyone have any idea what values to start with?

    #23072
    bni
    Participant

    I did some more experiments with Line 4x mode, and I think I found the optimal settings:

    Line 4x (Generic 4:3)
    H. samplerate 1560
    H. synclen 72
    H. backporch 170
    H. active 1280
    V. synclen 3
    V. backporch 30
    V. active 270

    Mainly what I did from defaults was decrease V. active a little bit, and then centered the picture with V. backporch.

    This gives a “4:3 1080p” mode that the 4K TV handles optimally (scaling and motion).

    Picture was a bit dark now, so I Increased brightness in OSSC a bit from 128 to 138 for all three colors (R/Pr G/Y B/Pb offset)

    Here is some photos of the result (colors are off from camera, doesnt really do it justice):

    Pinball Fantasies

    Flashback title screen

    Flashback info overlay

    #23078
    jdryyz
    Participant

    Wow! Good job!

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