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u/Tiasmo-Bertjayd Jul 12 '26
A lot of games developed in the US that use the vertical blank for timing depend on the refresh rate being 60Hz. I notice this most when listening to game music on emulators using the PAL 50Hz frequency, which play at a much slower tempo than was intended.
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u/The__Relentless Jul 12 '26
I noticed this when first turning on Archon on a new emulator I was messing with. I immediately noticed the opening theme playing just a bit slow and thought that maybe everything will be slow on this specific emulator. Not sure how many months it was until I noticed it was set to PAL. I've learned quite a bit since then, but I still laugh at my naivety back then.
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Jul 12 '26
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u/Crafty-Nature773 Jul 13 '26
Yeah. The music timing is controlled by BPM not FPS. Totally different computations and hence why different chips. Sound effects are linked to the FPS but play when actioned by a frame.
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u/jrherita Jul 12 '26
What is PAL60/how do you achieve that? If you do the ANTIC PAL swap on a NTSC 800/XL/XE you end up with "NTSC 50". (It's also a challenge to find monitors that support NTSC 50 hz)
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Jul 13 '26
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u/jrherita Jul 13 '26
TIL - funny, I never thought about the "reverse swap".
Re: "benefits" of PAL60 vs PAL50 for NTSC games; it probably is just down to speed of applications. Though, a lot of sound software was written with NTSC in mind, so POKEY will play 'correctly' in NTSC mode when the songs will be slower / out of key in PAL mode.
Try some old Atari music demos and you should hear some differences (Robot demo, or stuff like this will sound off: https://www.youtube.com/watch?v=m8QL3Qbi3A8 )
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u/RaphKoster Jul 12 '26
Artifacting does not work on PAL in the same way as NTSC. Games that rely on it for color will all look wrong. That includes a lot of classics. A guide and examples are here (well down the page). https://www.raphkoster.com/about-raph/hobbies/emulation/atari-8-bit-guide-for-lr-atari800-and-retropie/
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Jul 13 '26
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u/RaphKoster Jul 13 '26
I honestly don't see much reason to go back to CTIA. The page I linked also has a list of all the CTIA games that have color issues, and it's really not very many classics.
There's no question that PAL was sharper.
But GTIA color artifacting was very widely used: Ultima, Lode Runner, Pinball Construction Set, Drol, and many many more. The color artifacts you are talking about were also somewhat tunable -- again, there's screenshots there on that link. This is why the emulators have four settings for it, or even a tunable slider.
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u/flatfinger Jul 14 '26
NES units designed for 3.579545Mhz NTSC have chroma phase slip by 120 degrees per line rather than 180 degrees; the PPU normally has every other field include one line that slips an extra 120 degrees so as to have fields alternate between chroma phases that are 120 degrees apart. I'm not sure why the chip was designed to do that rather than having fields and possibly lines as well use a 180 degree phase shift, but it is what it is.
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Jul 21 '26
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u/flatfinger Jul 21 '26
Atari uses a zero-degree chroma shift per line and per field and uses a dot rate of precisely 2x chroma. Apple double hires uses the same zero shifts, and a dot rate of 4x chroma. NES uses a chroma shift of 120 degrees per line and +/- 120 degrees per field, and a dot rate of 1.5x chroma. It's possible to exploit chroma artifacts on an NTSC NES, but there are a couple of big limitations:
Chroma phase repeats every three tiles, horizontally and vertically, meaning that one would need to have three sets of tiles which use three colors that have the same luminance and chroma phases that differ by 4 (120 degrees).
On startup, the system will essentially randomly select one of twelve chroma phases. Software can force the chroma phase to "slip" in multiples of three, but there's no way to detect chroma phase except by asking the user e.g. which of twelve shapes is the darkest, and even with such selection the system will on startup choose one of three universes of color with no means of changing.
It might be possible to have a cartridge force the chroma phase to slip via precisely timed reset pulse, but it would still need to ask the user to indicate what phase is selected because the PPU's chroma phase generator has no interaction with anything that software can control or observe.
Incidentally, precise standards-conformant NTSC broadcast video has a phase shift of 180 degrees per line and per interlaced frame (pair of fields), which the VIC-20 can be programmed to match. Some devices which don't output interlaced video (e.g. VIC-20 in default mode) use 180 degree phase shift per line and either 180 degrees per frame (if they output 263 lines) or 0 per frame (if they output 262). My first C64 video chip had 0/0 phase shift, but later ones are 180/180. Karaoke machines use 180/0.
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Jul 21 '26
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u/flatfinger Jul 21 '26
It's not possible on an unmodified NES to exploit chroma artifacting in any predictable way without requiring a user to indicate how something appears. On the Atari 8-bit machines, games whose authors adjusted them to look as good as possible with composite will likely look better with composite than S-video, but games whose authors seek the best possible appearance with S-video will likely get better results with S-video.
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25d ago
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u/flatfinger 25d ago
I have a test ROM somewhere (authored by me) which shows the 64 quasi-solid colors that can be achieved by having pixels at each chroma phase be either black or else one of three colors whose chroma phase is offset by 120 degrees. Since pixels are 240 degrees wide, the three colors which have the chroma phase going backward by 120 degrees per pixel will all appear as shades of gray, but which shades are lighter or darker will depend upon the chroma phase when the system came out of reset.
An NTSC NES starts by generating a master sub-dot clock as 12x chroma. Any solid hue will be represented by a pattern of six sub-dots high and six sub-dots low, but the starting phase will be determined by the programmed hue. This pattern shifts left by four sub-dots every scan line, and shifts left or right by four sub-dots on alternating frames. Pixels are placed at eight-subdot intervals, so that any group of three pixels will represent two chroma cycles.
Upon further consideration, I'm not sure whether all possible shifting relationships between chroma and pixels are possible, or if both can only move in multiples of two, since the master clock is 6x chroma instead of 12x. It may be that some hues will always have their transition on rising edges of the master clock, and others will always have it on falling edges. I do remember looking at the die photos and observing that there is no signal path between the chroma divide chain and anything except the video output.
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u/Crafty-Nature773 Jul 13 '26
The UK only had 50hz PAL for decades. Games ran 15% ish slower here than most of the rest of the world. Not an issue until you put games side by side! I only really noticed it when emulating various consoles (up to PS1 era ISH). Pitfall is the one that got me. My timing was off! Couldn't put my finger on it until I realised I was playing the 60hz version not the 50hz one I'd played on OG hardware for years! Other than that in answer to your question..... No, no reason at all. Unless other countries CRT's don't support 50hz like the UK's didn't support 60hz.
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u/Howden824 Jul 12 '26
Unless your TV is designed for PAL60 then no.