Dealing with 50hz CRT Flicker

[FoxbatStargazer]

I grew up with an Atari ST in America, so I ended up playing a lot of Euro-developed games on 60hz monitors and TVs. Never really had much of a problem with 60hz flicker and still generally don't. These days though I am trying to run things at 50hz since many of these euro-games seem to run better or more as intended, especially if you go over to the Amiga side that is often less tolerant of forcing to 60hz...

Being in America finding cheap/free consumer CRTs that will sync to 50hz isn't so common now, but VGA CRTs will happily oblige. However I'm finding it hard for my eyes to deal with the very visible flicker at 50hz on VGA CRT, it gives me a headache after a few minutes and makes it difficult to sit through even moderate gaming sessions. Amiga games like Turrican and Robocod scroll great at 50hz on CRT but the flicker is still getting to me, especially on bright backgrounds.

Just curious particularly for Euro experiences, does or did the 50hz flicker bother you? Is flicker less noticable on more appropriate displays like 15 khz PAL monitors, PVMs or euro consumer sets? Do they maybe have more phosphor persistence than VGA CRTs that were mostly designed for 70+hz? Do you still enjoy 50 hz on CRTs or use other solutions now?

[MiSTer_Kirk]

It's the VGA CRT, once you go under 60hz they flicker like mad. My Viewsonic 15" VGA CRT will flicker quite badly on anything below 60hz. Yet, none of my CRT monitors like the Philips range, or the Amstrad CTM644, Atari SC1435, Acorn AKF30. etc.. Or any of my CRT TVs from Sony, Panasonic, etc.. none of them flicker, and look good at both 50 and 60hz.
Can you get the Philips 8833 range in America ?
Or perhaps a Sony PVM ? I have a 9" HR Trinitron, and a 14" 1442 QM, and they also don't flicker at 50 or 60hz.

[Chris23235]

In general the flickering is worse on VGA monitors then it was on RGB CRTs back in the day, because the persistence of RGB monitors was longer then on VGA monitors that were intended for higher refresh rates.

[Jegriva]

I grew up watching 50Hz CRT. Literally two decades, before I bought my first LCD tv in 2006. Now... I am now used to it as I was, and swicthing from 60 to 50 is really jarring.

[FoxbatStargazer]

It's the VGA CRT, once you go under 60hz they flicker like mad. My Viewsonic 15" VGA CRT will flicker quite badly on anything below 60hz. Yet, none of my CRT monitors like the Philips range, or the Amstrad CTM644, Atari SC1435, Acorn AKF30. etc.. Or any of my CRT TVs from Sony, Panasonic, etc.. none of them flicker, and look good at both 50 and 60hz.
Can you get the Philips 8833 range in America ?
Or perhaps a Sony PVM ? I have a 9" HR Trinitron, and a 14" 1442 QM, and they also don't flicker at 50 or 60hz.

I actually might still have an Atari ST color monitor, though it was bought when new in America so I don't know if that will handle 50hz. Would have to wire up a cable too I imagine...

Edit: I think I had something closer to the SC1224. Will have to see if I can find it...

[jlancaster86]

I'm Australian, so I grew up with 50 Hz TVs (PC monitors were typically 60 Hz or higher). I was used to it at the time, but I honestly can't stand the 50 Hz flicker these days. But I also avoid PAL games like the plague now, so it's hardly an issue for me.

[MiSTer_Kirk]

Edit: I think I had something closer to the SC1224. Will have to see if I can find it...

The SC1224 should do 50hz, it was built for the ST, anyway. Problem is, if I can remember, it has a fixed input connector, so you probably won't be able to make use of it. Not sure if it could be adapted or not. This was the reason I got the SC1435, as it's just a rebranded Philips 8833 MkII.

One thing to note with the SC1224, it uses two syncs, Hysnc and Vsync. So getting a SCART connection/Adapter might be difficult as the SCART would need composite sync.

[FoxbatStargazer]

Bumping with an update because I finally dug out my old NTSC Atari 520 ST and its accompanying SC1224 monitor and surprisingly everything still works! The monitor is labeled as "version 2" on the back and has a separable monitor cable, which I read indicates it is of JVC manufacture. The picture quality is quite good, high contrast and sharp with thin but soft scanlines. The only issue is some super obvious jailbars, although it seems like that sort of thing is usually more the fault of the computer or console than the monitor?

While it is an NTSC ST, I have one commercial game I know of that had a 50/60hz toggle with F10 (viking child), and also Turrican 1 (or at least its demo) seems to force 50hz. The monitor indeed syncs to 50hz fine, with surprisingly small changes in aspect ratio and position. The only problem is the jailbars flicker quite noticibly when in 50hz when they were more stable and subtle at 60. Really with the jailbar flickering its almost worse than a VGA CRT at 50hz! I hope this is just a flaw of the ST rather than the monitor...

As for repurposing this display for Mister, well there do exist some cables and adapters for connecting STs to VGA, such as this one. Since translating the RGBHV should only require rewiring (leaving out 15 vs 31khz since these adapters should not be addressing that), it seems that I can probably also plug this adapter into the monitor's video-in port and feed 240p into it using a VGA cable from the Mister? I'm just hoping the monitor doesn't get damaged if its briefly fed unsupported resolutions like a forgotten scandoubler setting or interlaced.

In the meantime I have discovered at least one consumer CRT TV brand in America that can sync to 50hz over component: Advent, or at least a flat 20" model over the component input. Maybe some other Advent models can do so as well. It just sounds like you need to avoid composite or RF because they don't understand PAL color encoding, but that should not be an issue with S-video or component, or maybe if you RGB mod one.

[kalach.x]

As a citizenship of European country I do not have and can not have any issues with 50Hz

But in all seriousness some VGA monitors are terrible for 50Hz.
Not all but if you take fancy Trinitron and try to run 50Hz you are in for a bad time.

I have cheap 17" LiteOn and it has pretty much the same persistence as PVM apparently because it doesn't flicker like mad. But when I run 50Hz on SONY GDM-FW900 my eyes want to pop-out. It is however mostly an issue with staring at white windows in operating systems with GUI. For games it is flickery but much more manageable, even if game is itself quite bright.

My recommendation is getting PVM. Best one with darker screen as those will have better contrast and be less susceptible to getting washed out colors when there is some light in the room. You want light in the room for eye-comfort.

[FoxbatStargazer]

Yeah I noticed that brighter scenes are absolutely brutal, like as you head up higher in Turrican 2 1-1. Or heck just throw up a white screen. When measured by this test the SC1224 Version 2 seemed only a mild improvement over a VGA monitor. The display is overall much more stable and cleaner at 60hz, not surprising with Atari being a U.S. company even if most of their customers were overseas.

With SD TVs being designed primarily for 480i, I guess it makes sense that they would have longer phosphor persistance and tend to handle 240p/50hz better. With PVMs going for hundreds I was just hoping to identify some cheaper alternative in the states.

[LamerDeluxe]

I've worked on an interlaced 50Hz display for years, creating 3D animations on the Amiga. I don't have a problem with it. A friend of mine couldn't even handle 60Hz displays.

[caad]

Yeah but 15kHz displays typically seem to have a little slower phosphors than VGA ones, so the flicker isn't quite as noticeable.

[elvis]

Joining in with a lot of the PAL gamers. I grew up in Australia, and 50Hz was the standard. I spent my entire childhood playing games on 50Hz CRTs, from the 8 bit era and up.

Fast forward to today, and 50Hz really hurts. I would almost say I'd rather go to OLED if I was forced to play 50Hz games again (as a retro console gamer, I've moved over to NTSC entirely for actual gaming).

Another cool feature would be double-scanning. Most (S)VGA monitors can do 240p at 120Hz fine. I haven't tested 288p @100, but I assume it would work too. That would be fantastic for Amiga/C64 gaming in particular. I can do that out of a Pi easily, but I haven't tried fiddling with MiSTer modelines to see if it's possible.

[kalach.x]

Another cool feature would be double-scanning. Most (S)VGA monitors can do 240p at 120Hz fine. I haven't tested 288p @100, but I assume it would work too. That would be fantastic for Amiga/C64 gaming in particular. I can do that out of a Pi easily, but I haven't tried fiddling with MiSTer modelines to see if it's possible.

It can be done currently but scaler does not have ability to match to double the framerate so you would be forced to use vsync_adjust=0

Biggest and most glaring issue with 240p@120Hz or 288p@100Hz is effect of double images. 50fps game on 50Hz CRT is perfectly sharp no matter if objects/backgrounds are stationary or moving and on 100Hz CRT when things start to move you see double images. For 25fps games there would be four images. On flicker-free LCD or non-strobed OLED (like typical OLED TV) the refresh rate is virtually infinite so there is so many "double" images your eyes pick this as motion blur.

So I would not recommend such mode even if it was made to sync with core's frequency * 2 except maybe running games which already have double images (25/30fps or slower) or operating systems. Though for those use cases if double images and/or flicker bothered me I would just use LCD or even better: OLED

[FoxbatStargazer]

The double images aren't horrible in practice but it does feel a bit more like you are looking at an LCD, which undermines the point a bit. I just find trying to manually match the refresh kind of annoying. Sub 50/60 FPS was also a lot more common on computers than consoles, even the Amiga, so double images were already part of the territory.

[elvis]

Biggest and most glaring issue with 240p@120Hz or 288p@100Hz is effect of double images. 50fps game on 50Hz CRT is perfectly sharp no matter if objects/backgrounds are stationary or moving and on 100Hz CRT when things start to move you see double images. For 25fps games there would be four images. On flicker-free LCD or non-strobed OLED (like typical OLED TV) the refresh rate is virtually infinite so there is so many "double" images your eyes pick this as motion blur.

I've only tested in on PC (S)VGA CRTs. Never on a domestic TV nor an OLED. On one of those, it works perfectly, no double-image effect. Looks and feels just like regular 50Hz, but the flicker is removed entirely thanks to the second frame. Same effect as playing a 30FPS game on a 60Hz display.

I wouldn't bother at all on an OLED, because it's "store and hold" anyway, and the 50Hz framerate issue isn't noticeable. 50Hz on CRT is where I really notice the flicker, and again I've only ever tried the "double frame rate" on PC monitors, not 100Hz TVs (which I never use for a bunch of other reasons).

[FoxbatStargazer]

Only took a month but I finally received this color Atari ST to VGA adapter. I mentioned this as a possible route for a good? PAL capable monitor over here in America, so I thought I would follow up with my findings for using it with Mister.

This adapter is intended for outputting 15khz over VGA from your Atari ST but of course, I wanted to use it for the reverse direction, to take Mister and input it into my Atari ST SC1224 version 2 NTSC monitor! While the adapter fit my ST perfectly, I had to push in hard to get it into the monitor. Something about the top guiding indent seemed to be shaped differently. Anyway it is quite snug now so hopefully nothing was damaged in the process.

Once my Mister was thoroughly flipped to outputting 15khz on the analog I/O port, everything did just work with the monitor. This little monitor is incredibly sharp horizontally, probably on the lower/small PVM side, and with gentle scanlines on the vertical. Zoom in and you can see the similarity of this JVC shadow mask to some of those we have in Mister now! Fortunately, the jailbars I observed earlier when using my ST were indeed the fault of that computer, zero jailbars gumming up the display with Mister! Unfortunately, the colors from Mister I/O port look kind of dim and especially lacking red here. I've read that the ST's video out is relatively "hot" so the monitor might be calibrated for higher than average levels.

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This particular adapter had a minijack for audio, which surprisingly also worked for putting audio into this monitor's built-in speaker. The Atari ST could only produce mono audio and I think I'm only hearing mono, but somehow the stereo feed is getting combined instead of simply taking one channel. (easily verified with sonic's rings sound or any Amiga soundtrack with full stereo)

Now 50hz the monitor does fine, although the amiga output isn't centered too well. It's also still fairly flickery, although less so than a VGA monitor and Turrican felt smoother to play.

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Suprisingly it will also sync to 200p/70hz, although the top few scanlines were warped and the image a bit squashed. Maybe adjusting modelines will yield better results.

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I had read that this monitor can't handle interlaced content... but it's working perfectly here in Sonic 2. I also got some more traditional interlacing with the PSX bios, although it has a bit of bob/jitter which seems to be the norm for sharper CRTs. It also weirdly seems to handle Sync on Green (which STs never used), so you could probably even play xbox in 480i with a softmod for RGsB over component cables. edit: This is not true, HV sync is required, see below.

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The Atari ST had some honking huge borders, and this monitor is currently calibrated to center the NTSC from the original machine pretty well. NTSC Atari ST output is also a little tall and this monitor seems calibrated to flatten that out a bit, meaning other NTSC cores look slightly fat. The Mister Atari ST core looked slightly off-center and as you can see here, using other NTSC cores like Genesis had quite a bit of the left side pushed into overscan. The Amiga core in 50hz mode could also go above the top and bottom borders too.

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There are some potentiometers on the back which should aid in adjusting the overscan and aspect ratio. One addresses brightness (but what I really want is more contrast), none of them seem to adjust color or hsize though. (They are also hilariously a bit misaligned with the holes on the case, negating the safety feature and requiring adjustment with the case off.) I'm a bit hesitant to touch them though since they are currently well calibrated to 60hz Atari ST content. Maybe there is a good way to record their current positions?

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I think the other things I can kind of adjust, but the reds being a bit low is kind of a bummer. They didn't seem to be lacking from a real ST at all. Maybe creating a custom color correction profile in mister can compensate somewhat, or the adapter can be somehow modified? Hopefully someone more knowledgable has a suggestion.

[FoxbatStargazer]

Don't know who cares about this dumb monitor but I thought I'd leave some more info here for posterity, especially a WARNING about voltage levels!

A big WARNING here from comparing the VGA and ST pinouts: the ST only outputs 1v on H and V sync, but Mister can put out at least 3 volts. This is mentioned as a problem for using Mister with SCART equipment and it applies here as well. Over a long period of time its possible you fry your equipment and people have reported doing so, so do not plug your Mister into old 15khz displays using H/V sync without properly attenuating the voltage. Since it isn't safe to plug the Mister into this monitor without using a similar resistor, I've discontinued using it for now.

The other issue this comparison revealed is that the RGB pins are up to 1 volt on the ST, while VGA only goes up to .7 V. So that would explain the dimness. I did adjust the brightness potentiometer to get some useable display, but this lowers the contrast and leaves colors faded compared to what you can get from an ST input. So some way would be needed to amplify the voltage levels for ideal input. Best I could find on Amazon was some 2-way VGA splitter and amplifer that claimed to increase usuable transmission distance from 25 to 200 feet, but I didn't find that it improved the RGB levels at all. Not sure what device could do this job.

Also contrary my earlier thoughts, Sync on Green is not supported. If you don't have Hsync then you just get a black picture, and if you try to use composite sync (vsync into hsync) you get a rolling picture. However the monitor does somehow filter out the extra green that is added by the Sync on Green line, maybe there is some JVC circuitry that handles this but it does not unfortunately use the SoG for any kind of sync.

As for the other potentiometers. Fiddling around with them can yield better centering and sizing, and I got something that worked pretty well for most console cores. Since there is no width potentiometer though (at least exposed on the back), you are stuck with a fair amount of overscan in the consoles. Most unfortunately, Amiga is very non-cooperative with games choosing to center all over the place, you basically need to use the scaler and a decent amount of blank padding to get something consistently useful.

Finally contra my screenshot here, you can get 70hz working perfectly with no tearing, by just adding some more vertical back porch. There's plenty of space at 200p to do so, and low res DOS games do look surprisingly good in 15khz and now with native refresh.

[FoxbatStargazer]

I finally found a solution to the voltage issue: Extron's P/2 DA4xi VGA Distribution Amplifier. Outputting to four monitors is complete overkill for me, however this thing has a very useful switch that changes .7 volt RGB input to 1.0 volts output, which perfectly matches the SC1224's specifications. Now images look vibrant, high contrast and beautiful, just like an Atari ST would, but without any of the messy jailbars and instability of that old system. These can also be readily found on ebay for $20-30 so not hard to pick up at all.

Extron has quite a few signal processors that have amplification features, but most seem focused on "peaking", which they explain here. Basically in long cable lengths, changes in signal level tend to get rounded off, yielding a blurry picture. Peaking tries to overshoot the changes to compensate and sharpen the image. This is very much not what I need because the issue wasn't long cable length, it was just that the overall voltage was low. The DA4xi is just a simple +3 db boost to 1 volt peak-peak, no peaking, and higher amplitude than most of Extron's other RGB video processors are capable of, so it is the perfect remedy to get VGA standard voltages up to Atari ST spec.

Additionally the Version 2 JVC user (NOT service) manual lists specifications for my monitor, and it includes 5 V TTL sync. So whatever the Atari ST is producing, the monitor is safely within spec for Mister's default H/V sync. So using Mthe DA4xi with the boost to 1v is all that is needed for Mister RGB out to conform to monitor specifications and have a great experience.

I've also found what should be the horizontal size/ width control, as with the service manual for the other version, there is a metallic coil with a black hexogonal prism in the center pointing upward out of the main PCB, on the one side between the screen and the flyback. According to the manual you use a tool to turn the hexagon to adjust width, haven't tried it yet but I intend to later. There's also smaller blue potentiometers inside that control other settings like RGB drive/cut and linearity, all are labeled on the PCB. Some of them are hard to access safely while the monitor is on so I'm going to need some better tools to attempt.

[thisisamigaspeaking]

Biggest and most glaring issue with 240p@120Hz or 288p@100Hz is effect of double images. 50fps game on 50Hz CRT is perfectly sharp no matter if objects/backgrounds are stationary or moving and on 100Hz CRT when things start to move you see double images. For 25fps games there would be four images. On flicker-free LCD or non-strobed OLED (like typical OLED TV) the refresh rate is virtually infinite so there is so many "double" images your eyes pick this as motion blur.

I've only tested in on PC (S)VGA CRTs. Never on a domestic TV nor an OLED. On one of those, it works perfectly, no double-image effect. Looks and feels just like regular 50Hz, but the flicker is removed entirely thanks to the second frame. Same effect as playing a 30FPS game on a 60Hz display.

I wouldn't bother at all on an OLED, because it's "store and hold" anyway, and the 50Hz framerate issue isn't noticeable. 50Hz on CRT is where I really notice the flicker, and again I've only ever tried the "double frame rate" on PC monitors, not 100Hz TVs (which I never use for a bunch of other reasons).

So if I want to determine whether a particular (S)VGA CRT is capable of running 288p 100Hz what do I need to look out for? Are horizontal scan rate and vertical scan rate all I need to know, so any monitor capable of 100Hz vertical and 31.778KHz horizontal would work with 288p100?

[elvis]

So if I want to determine whether a particular (S)VGA CRT is capable of running 288p 100Hz what do I need to look out for? Are horizontal scan rate and vertical scan rate all I need to know, so any monitor capable of 100Hz vertical and 31.778KHz horizontal would work with 288p100?

Specific to SVGA CRTs, the hsync rate is generally all that matters. In that regard, 576p50 is exactly the same hsync rate as 288p100, and any CRT that can do one should be able to do the other.

[thisisamigaspeaking]

So if I want to determine whether a particular (S)VGA CRT is capable of running 288p 100Hz what do I need to look out for? Are horizontal scan rate and vertical scan rate all I need to know, so any monitor capable of 100Hz vertical and 31.778KHz horizontal would work with 288p100?

Specific to SVGA CRTs, the hsync rate is generally all that matters. In that regard, 576p50 is exactly the same hsync rate as 288p100, and any CRT that can do one should be able to do the other.

Thanks. Good to know.

So do you know how they usually arrived at the vertical frequency range? I'm not finding an exact match between the two when I look at specs, for example assuming 480p or 600p as the minimum they thought someone would run the monitor at.

[FoxbatStargazer]

Virtually any half-decent SVGA monitor should be able to handle something around 100hz/ 288p. It's worked for every one that I've tried. You might have to increase the vertical blanking if the refresh is a bit low for the monitor but that's easily doable with video_mode.