General question regarding 50/60hz and composite adapters on CRT

[eobet]

This is a fuzzy question and I'm getting old also forget technical details... but I distinctly remember PAL vs NTSC games on Atari 800 playing music at different speeds... but on the Atari ST the music speed stays the same when switching between 50/60hz... then again, my JVC display says NTSC either way and I'm using Antonio Villena's composite adapter set to NTSC... and yet the "overscan" (probably wrong word in this case) changes. Anyone know the technical reasons for all of this and care to untangle it for me?

[FoxbatStargazer]

NTSC/PAL also refer to very distinct color encoding standards when it comes to composite video. Its likely the Mister plus whatever boards is still spitting out NTSC style composite color even when in 50 hz. When your TV reports NTSC it might be referring more to the color standard, it looks like the refresh rate is changing properly.

The Atari ST would default to 50/60hz at boot depending on providing a US or EU bios. Software could also override this at any time. Generally software that does the overriding is going to be aware of what refresh rate is in play and might adjust other things like music accordingly. Or it could just be Prophecy: Viking Child which has an in-game 50/60hz switch which also makes the music go faster or slower...

Anyway there are many examples of ST music going slower/faster when you force the other mode. Try booting up Magic Pockets with a US vs EU bios and the opening tracker jingle will play fairly different. Another one is Rick Dangerous. I'm not sure software was any good at detecting what region your bios was, hence why there are distinct NTSC and PAL region variants of many commercial games. At least with ST the usuable resolution never changed... low res was always 320x200 no matter what.

[eobet]

NTSC/PAL also refer to very distinct color encoding standards when it comes to composite video.

Was it not also something called "line count", but that perhaps only has to do with broadcasting?

Either way, thank you for the information and the examples! I will test them when I get a chance and experiment more (I grew up with PAL so it's interesting to be able to test NTSC using the MiSTer hardware and adapters now). Do you happen to know why the picture changes size when I flip between 50/60 though? I don't remember that from 30 years ago, but my memory might be equally as fuzzy as my questions or perhaps it's just the way that this PVM handles the signals compared to the consumer TVs I had back then...

[FoxbatStargazer]

Yes the line count is different for 50hz vs 60hz. 50hz needs more lines to maintain the same horizontal refresh (15 khz). So the same 320x200 is going to look more squished at 50hz because more black lines are being "drawn" above and below.

There was such a thing as PAL60 for a time, where you had pal-style composite color output at 60hz for compatible TVs. For a long time the PAL/NTSC broadcast standards usually bundled color coding and refresh rate but the two are technically independent, you can use PAL color at 60hz or NTSC at 50hz with a compatible display.

[eobet]

Not to derail my own thread... but would it be possible to use a custom video mode to expand the image on a CRT and eliminate the borders?

I've tried some games available on both the Atari ST and the Sega Megadrive and it's interesting to see that even though they both run 320x200/220, the images they display on my CRTs are very, very different in size.

I ask because the AO486 core basically requires this and some of the configs I've tried from this thread made the image too large to fit the screen...

[FoxbatStargazer]

You can easily control horizontal size and positioning on a real CRT by using the scaler to create a video_mode and adjusting the horizontal blanking parameters. You can also control vertical positioning by messing with the vblank, but size might be harder to adjust unless you change the refresh rate from the original (which is totally possible with vsync_adjust=0 although probably not worth the frame stutter...) The process for doing this is basically going to be the same as on ao486.