If DOS is a concern: 70Hz support without frame skipping. Also input lag.

Unless you need specific DOS mode for game to work, it doesn't matter what monitor you use (ie. they will all display image).
Fluidity is biggest issue though, as digital only monitors (ie. DVI/HDMI/DP only) are usually limited to 60Hz under DOS (since most VGA to whatever digital adapter can't convert over 60Hz to usefull signal on those ports).

Also, video card is very important in retro compatibility testing.
Example : Monitor works fine with HDMI 2.0 Maxwell (or whatever newer card), but plugged to GF4 Ti makes it behave oddly in DOS/Windows.

The Serpent Rider wrote on 2023-03-18, 12:29:

If DOS is a concern: 70Hz support without frame skipping. Also input lag.

Thanks

Do you have a good game to test this with?

agent_x007 wrote on 2023-03-18, 14:52:

Unless you need specific DOS mode for game to work, it doesn't matter what monitor you use (ie. they will all display image). Fl […]
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Unless you need specific DOS mode for game to work, it doesn't matter what monitor you use (ie. they will all display image).
Fluidity is biggest issue though, as digital only monitors (ie. DVI/HDMI/DP only) are usually limited to 60Hz under DOS (since most VGA to whatever digital adapter can't convert over 60Hz to usefull signal on those ports).

Also, video card is very important in retro compatibility testing.
Example : Monitor works fine with HDMI 2.0 Maxwell (or whatever newer card), but plugged to GF4 Ti makes it behave oddly in DOS/Windows.

I actually own an AOC 1440 monitor with all the bells and whistles and it‘s completely useless. Doesn‘t display any of the Dos resolutions and even with a scaler the image stays blank. To make matters worse, standard windows resolutions like 800x600 are simply centered on the screen and scaling can‘t be forced. Totally useless.

However, I read Dell manuals and see that most newer screens run at 70Hz for 720x400 and others. And I think my OSSC should just pass that through, no?

d3vilsadvocate wrote on 2023-03-18, 20:02:

The Serpent Rider wrote on 2023-03-18, 12:29:

If DOS is a concern: 70Hz support without frame skipping. Also input lag.

Thanks

Do you have a good game to test this with?

Commander Keen 4 overworld is easy to use for testing for judder. @ 70Hz, you should get smooth scrolling on the overworld. If only 60 Hz, the judder is obvious.

For testing input lag, the easiest way is to hook up the LCD and a CRT side-by-side on the same setup (dual video). Then start a timer counting in milliseconds and take a photo. The difference in time captured will be the input lag.

Judder and frame skipping are separate issues. Former is caused by uneven frame pacing. But yes, in both cases scrolling won't be perfectly smooth. DOS applications are not required, just use SmoothFrog or BlurBusters UFO test with any custom resolution (both modern Nvidia and AMD allow to create it) set at 70/75 Hz.

Shponglefan wrote on 2023-03-19, 02:36:

d3vilsadvocate wrote on 2023-03-18, 20:02:

The Serpent Rider wrote on 2023-03-18, 12:29:

If DOS is a concern: 70Hz support without frame skipping. Also input lag.

Thanks

Do you have a good game to test this with?

Commander Keen 4 overworld is easy to use for testing for judder. @ 70Hz, you should get smooth scrolling on the overworld. If only 60 Hz, the judder is obvious.

For testing input lag, the easiest way is to hook up the LCD and a CRT side-by-side on the same setup (dual video). Then start a timer counting in milliseconds and take a photo. The difference in time captured will be the input lag.

I second this, Commander Keen IV is a good compatibility tester.

Ironically, though, it uses EGA modes - and real EGA hardwate used to run at 60 Hz all the time. 😉

Still, on SVGA cards in their native VGA mode (ie, no use of mode utility, no emulated EGA in silicon), it runs at 70 Hz by default.

Another thing I use for testing LCDs is a checkerboard pattern.
I have a bitmap somewhere that I share, if there's any interest. 😃

The Serpent Rider wrote on 2023-03-19, 03:28:

Judder and frame skipping are separate issues. Former is caused by uneven frame pacing. But yes, in both cases scrolling won't be perfectly smooth. DOS applications are not required, just use SmoothFrog or BlurBusters UFO test with any custom resolution (both modern Nvidia and AMD allow to create it) set at 70/75 Hz.

ah thanks, that turned out to be useful. With 75Hz at 75FPS in the UFO test (and some of the others they have) I get massive skipping that looks somewhat similar to judder and also tearing, but it's even more noticable than these. With 60Hz 60FPS the image is buttery smooth.

That's on a Dell U2415b btw which "supports" 75Hz refresh rates...

Shponglefan wrote on 2023-03-19, 02:36:

Commander Keen 4 overworld is easy to use for testing for judder. @ 70Hz, you should get smooth scrolling on the overworld. If only 60 Hz, the judder is obvious.

Commander Keen is not actually panning the map or game screens at 70hz natively, but only at 35 hz. However, even then, the scroll in the game is not hard-locked perfectly on 35hz, but will occassionally miss frames.

Games off the top of my head that come to mind that do have smooth panning motion:
- Lemmings game main menu, there is a 70hz scrolling text screen,
- One Must Fall, although there are no specific 70hz visible panning elements, but you'll have to play the game to "feel" it.
- Pinball games in their table intro view, where the game pans across the pinball table when gameplay is not yet activated. (these do use different video modes with different refresh rates, so set them to lowest 320x200 to get a 70hz mode)
- The demo "Yo!" from Future Crew does smooth panning at 1px per frame, although now actually I can't recall 100% if that demo was 70hz, or if it actually was 60hz, I'd have to check. Though this is still good for smooth scroll testing.

I have been validating monitors and graphics cards in my test lab for DOS use. Here are parts of my test suite, all of this stuff is of course subject to your own interest levels and what you care about:
- the common DOS video modes are:
- 320x400 (VGA mode 13h),
- 360x400 (CGA 00h/01h 40x25 text mode emulated on VGA),
- 640x400 (CGA 06h/EGA 0Eh mode 640x200 mode emulated on VGA),
- 720x400 (CGA 02h/03h 80x25 text mode emulated on VGA), and
- 640x480 (VGA mode 12h).
How well does it work in these?
- does the monitor allow a "force 4:3" mode on all of the above input modes? Or do some of them remain 16:10 or 1:1 aspect?
- does the monitor work with nonstandard game video modes on pinball games such as Pinball Fantasies, Pinball Illusions, Psycho Pinball, etc.?
- are the pinball games actually playable, or is video lag too much that hitting the ball in pinball games feels "off"?
- does the monitor work with nonstandard game video modes on non-pinball games such as Jazz Jackrabbit, Earthworm Jim, The Incredible Machine 1 and 2, Cyril Cyberpunk, etc.?
- does the monitor work with VGA Mode-X modes: Quake, Scorched Earth, Lost Vikings, etc.?
- does the monitor work with glitched video modes with negative horizontal or vertical sync porches, such as Jump & Bump (and the Pinball games)?
A good roundup of games with the above video modes can be found at http://nerdlypleasures.blogspot.com/2014/09/o … tions-when.html
- does the monitor quickly sync on changes in video mode? e.g. Lemmings and Jazz Jackrabbit change video modes during ingame transitions
- like already mentioned, does the setup work with different refresh rates: 50hz, 60hz and 70hz, not just to display an image, but to do so without frameskip?
- if SVGA/VESA/multisync modes are of interest:
- what are the max pixel clock, horiz. scanline rate and refresh rates the monitor supports? (from display specifications)
- does the SVGA 800x600@56hz video mode work? UniVBE's UniCenter tool allows testing these.
- do the SVGA 1024x768@86hz interlaced (43hz progressive) and 1280x1024@86hz interlaced (43hz progressive) video mode work? (last I recall trying with OSSC, I think OSSC itself did not support these, although it did support 800x600 interlaced, which is super rare to even exist on DOS graphics cards) Windows 3.1 with proper SVGA drivers allows testing this.
- do the VESA higher refresh rate modes work? E.g. 640x480@70,72,75hz? Or 800x600@60,70,72,75hz? UniVBE's UniCenter tool allows testing these.
- does the monitor work with SVGA text modes e.g. in Word Perfect? These are text modes like 80x(30-60) lines, 100x(25-60) and 132x(25-60) columns.
- if there is an audio external line-in 3.5mm jack, does it actually work while viewing display from HDMI input, and what is the audio quality of the built-in speakers like? (on Asus ProArt e.g. 3.5mm input does not work properly if HDMI input is active)
- does the setup work with exotic demo scene effects? LCD monitor VGA compatibility database allows testing these.
- how good is the panel picture quality? If it is e.g. an older panel, does it have ghosting in, say, Prince of Persia, where there is a white character running around against a black background, a good test for sharp contrasted animation.
- is the OSD menu and buttons comfortable to use? ("do I love this ergonomically paired with my retro PC")

You specifically mention Dell. I find that I have quirk notes marked down about the following Dell monitors:
- Dell 2007WFP 1680x1050:
- occassionally when the input resolution changes, there are random glitching scanline artifacts that appear on screen. These disappear if one goes in the picture aspect ratio settings, and switches aspect between Full <-> Aspect, and back. (for example, toggle the setting Aspect->Full->Aspect)
- 70hz video modes do sync, but do frameskip, and is not vsync-locked but exhibits visual tearing artifacts
- is unable to display 720x400 input video mode in 4:3 forced mode
- Dell 2007FPB 1600x1200:
- 70hz video modes do sync, but do frameskip, and is not vsync-locked but exhibits visual tearing artifacts

Thanks very insightful. A bit too exhaustive for my needs I think (i don‘t even fully know my needs yet I think) but very complete. Should be made into a reference here maybe?

I’ll be testing Dell displays with gsync soon. According to a friend, the S2721DGFA works at 70hz with no frameskipping in the ufo test.

To me, proper scaling of DOS resolutions, windows resolutions (ie no small image in the center of the screen) and no frameskipping at 70 is most relevant I think.

clb wrote on 2023-03-19, 08:28:

Commander Keen is not actually panning the map or game screens at 70hz natively, but only at 35 hz. However, even then, the scroll in the game is not hard-locked perfectly on 35hz, but will occassionally miss frames.

35 FPS will still create obvious judder on a 60Hz due to the uneven division of frame rate into refresh rate.

I just recommended this game because it's a) really easy to test, and b) glaringly obvious it's skipping frames.

Like I mentioned, SmoothFrog is a very powerful tool to test different scenarios: frame skipping, judder, VRR, etc.

Shponglefan wrote on 2023-03-19, 13:20:

clb wrote on 2023-03-19, 08:28:

Commander Keen is not actually panning the map or game screens at 70hz natively, but only at 35 hz. However, even then, the scroll in the game is not hard-locked perfectly on 35hz, but will occassionally miss frames.

35 FPS will still create obvious judder on a 60Hz due to the uneven division of frame rate into refresh rate.

That is true, though to clarify my wording, my point is that Keen will judder noticeably already even if the display does show 70 hz without frameskip, because Keen itself judders and is unable to lock on to that 35 hz. When playing the game, there will be several seconds long periods where it will properly sync panning at 35 hz, followed by several seconds long periods where it does not lock the panning at 35 hz, resulting in judder.

So, if using Keen to test this scenario, if you occassionally see periods where it looks smooth, then you can conclude 70hz is supported by the display.
But if you see periods where Keen panning judders, you cannot immediately conclude that 70hz would not be supported by the display - but you should keep observing for longer to conclude you "never" see smooth behavior in it. (it might be that Keen is not momentarily locking panning properly)

Double-checked now that the Yo! demo does render at 70hz without frame skip, so it can be used to check 1:1 pixel perfect panning support at 70hz.

d3vilsadvocate wrote on 2023-03-19, 10:03:

To me, proper scaling of DOS resolutions, windows resolutions (ie no small image in the center of the screen) and no frameskipping at 70 is most relevant I think.

Proper scaling of DOS resolutions (when VGA output is in question) is something I haven't seen any display ever to have. Unlike VESA VBE display modes, DOS display modes contain an "overscan border", which results in for example the VGA 640x480 video signal to instead be 656x496 pixels in size. (in that mode the border is equal 8 pixels in size on each edge, but in many other modes, that is not the case). Because of this overscan border, DOS resolutions are not properly upscaled in a pixel perfect (or resembling that, since the signal was already analog in the middle) manner.

VESA VBE mode standardization foregoes the VGA border, and 800x600, 1024x768 and higher video modes generally are just that, with no overscan border. So upscaling 800x600 to 1600x1200 for example will look very good as near as pixel perfect as possible.

CRT Terminator is being worked to resolve the issue of varying-sized CGA/EGA/VGA/SVGA borders in different video modes - it runs a dedicated video mode analysis subsystem to detect different video modes of what their expected borders should be, so it removes them properly from the output video signal without resulting in improper scaling further down the pipe.

What about testing monitor's DOS compatibility with this suite : LINK ?
Alternative option would 70Hz+ capture card... at least it takes less space than a new monitor.

I’m playing Lost Vikings at 640x480 60Hz right now and am getting a weird stuttering effect while side scrolling ok two different monitors.

Does anyone know what exactly that is? Ut‘s probably not frame skipping since it’s running at 60hz…