kennyPENTIUMpowers wrote on 2022-09-23, 03:46:

so i was playing chex quest on my P120 with a newish 22inch widescreen LCD and it makes the images look pretty awful.. apparentl […]
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so i was playing chex quest on my P120 with a newish 22inch widescreen LCD and it makes the images look pretty awful..
apparently chex quest runs in 640x400 but that doesnt seem right to me given it is based on doom, and i thought doom was a 320x200 game..(vanilla doom)..

so i went looking for a switch/option/config to set it higher and this lead to the issue of double scaning and 15khz etc(i dont really understand all this)

so the simple question is what is this fuss over 15khz monitors, why are they in demand and what actual difference does it make to the visuals?

15khz is more for stuff like the amiga , vga runs at 31khz so you shouldn't need to worry about that for doom.

AppleSauce wrote on 2022-09-23, 04:03:

kennyPENTIUMpowers wrote on 2022-09-23, 03:46:

so i was playing chex quest on my P120 with a newish 22inch widescreen LCD and it makes the images look pretty awful.. apparentl […]
Show full quote

so i was playing chex quest on my P120 with a newish 22inch widescreen LCD and it makes the images look pretty awful..
apparently chex quest runs in 640x400 but that doesnt seem right to me given it is based on doom, and i thought doom was a 320x200 game..(vanilla doom)..

so i went looking for a switch/option/config to set it higher and this lead to the issue of double scaning and 15khz etc(i dont really understand all this)

so the simple question is what is this fuss over 15khz monitors, why are they in demand and what actual difference does it make to the visuals?

15khz is more for stuff like the amiga , vga runs at 31khz so you shouldn't need to worry about that for doom.

Yup, VGA 320x200 is actually line doubled by the video card to 640x400, which is why it has a 31KHz vertical scanning frequency.

On the PC the big deal is that CGA/EGA games were designed with 15.7khz RGBI monitors in mind: you get 16 fixed colours and the monitor displays 200 scanlines with fairly large black areas between each line. You can play these games on a VGA system, but they are displayed in a double-scanned scheme where the monitor displays 400 scanlines with minimal black areas between the lines. So on a VGA the effect is "chunky" pixels.

Meanwhile the games designed for the VGA's 256 colour 320x200 mode (which is also double-scanned) were designed with these chunky pixels in mind, so for a game like Doom playing it on a regular VGA monitor is exactly how it was meant to be played. I don't think the original Doom would even have worked on a 15.7khz CGA/EGA monitor.

kdr wrote on 2022-09-23, 07:48:

On the PC the big deal is that CGA/EGA games were designed with 15.7khz RGBI monitors in mind: you get 16 fixed colours and the monitor displays 200 scanlines with fairly large black areas between each line. You can play these games on a VGA system, but they are displayed in a double-scanned scheme where the monitor displays 400 scanlines with minimal black areas between the lines. So on a VGA the effect is "chunky" pixels.

Meanwhile the games designed for the VGA's 256 colour 320x200 mode (which is also double-scanned) were designed with these chunky pixels in mind, so for a game like Doom playing it on a regular VGA monitor is exactly how it was meant to be played. I don't think the original Doom would even have worked on a 15.7khz CGA/EGA monitor.

I've run doom on a 15kHz display using the VGATV TSR. It looks quite nice actually

kdr wrote on 2022-09-23, 07:48:

I don't think the original Doom would even have worked on a 15.7khz CGA/EGA monitor.

it does. I couldnt afford monitor in ~95 and used ISA Trident card reprogrammed for 15KHz on 21' TV with Euro RGB connector and "special" cable (afair just an AND gate for syncs).

rasz_pl wrote on 2022-09-23, 13:01:

I couldnt afford monitor in ~95 and used ISA Trident card reprogrammed for 15KHz on 21' TV with Euro RGB connector and "special" cable (afair just an AND gate for syncs).

I was in similar boots, I used a Tseng ET3000 that had an EGA mode, made huge debug dumps on the BIOS switching video modes and found out how to make single scanned 320x200/256 for my kinda CGA monitor. It was 15kHz and RGB for sure, I had used it with my 8-bit micro before the VGA, EGA thenswitchin.It definitely wasn't limited to 16 cols. And then I made a TSR to handle video mode changes.

Fun fact, later I could make a similar TSR for an S3 Trio64 too, but IIRC I could only achieve interlaced low res and text modes which was quite wild 😁

rasz_pl wrote on 2022-09-23, 13:01:

kdr wrote on 2022-09-23, 07:48:

I don't think the original Doom would even have worked on a 15.7khz CGA/EGA monitor.

it does. I couldnt afford monitor in ~95 and used ISA Trident card reprogrammed for 15KHz on 21' TV with Euro RGB connector and "special" cable (afair just an AND gate for syncs).

The arcade cabinet scene used VGA's flexibility, too.
There was a time when PC motherboards were installed in such cabs, to run MAME (DOS port).
These DOS utilities helped keep using real 15KHz CRTs, required for authenticity.

Schematics..
https://www.geocities.ws/podernixie/htpc/cables-en.html

15khz CRTs are mainly a TV video game thing / 8 bit micro in that you get lag and improper visuals on a newer lcd.

https://m.youtube.com/watch?v=C_-9Rw5CJNE

On the PC side 15khz is just a compatiblity issue as modern screens usually won’t support vintage digital video card output

CGA might be an exception in PC history, though.
A real CGA card used NTSC compatible timings, too. 15KHz, 60Hz and pseudo progressive scan. And NTSC artifacts (Composite CGA).

these primitive sync combiners using sequential logic, or worse just passive components, are super yucky

I use an Extron RGB192V to get c-sync from my VGA cards