Linedouble mode: generic 4:3

[Galdelico]

I’m aware to be part of a minority, here, but after a bit of setting-around with the OSSC, I found myself loving the ‘analogue’, softer look of Linedouble mode – coupled with thick, 100% scanlines, and a few tweaks to gain/contrast values – over the crisper, brighter, but more emulator-like feel of Linetriple.

Now, this is more me wondering whether or not it’s possible to add this feature, rather than not being able to enjoy my experience without it… But, yeah, would it be doable to add a fix to the slightly wider (than how it should be) aspect ratio you get through Linedouble? Like an option similar to the ‘generic 4:3’ allowed by Linetriple mode.

I’m asking that because none of my PC monitors are able to perfect the screen ratio, due to them only providing widescreen(16:9)/original(wider 4:3)/and 1:1 video settings.

Thanks alot in advance! ^_-

[awe444]

Did you try adjusting the horizontal sample rate (and horizontal back porch) in the “Advanced Timing” menu for the “240p” mode? The default horizontal sample rate of 858 generally stretches 4:3 content into a wider 3:2 aspect. A sample rate closer to 800 might fix this for you (and you’d subsequently need to adjust horizontal back porch to re-center the image).

[Galdelico]

Wow, awe! Quite the appropriate nickname, man… Adjusting the Horizontal sample rate close to 800 worked, thank you so much!

Do you mind me taking advantage of you a bit more?
I’m still quite uneducated/unexperienced, so could you clue me about what exact value should I go for, with the Mega Drive (NTSC-J Model 2)? Is there a table where I can check what is the appropriate H sample rate number for the other systems I own? Or should I go with the 240p test suite, adjust the linearity by measuring the circles once, and then basically keep the same setting for all my OSSC profiles?

Thanks a million anyway!

PS – if it can help someway, my monitor – an LG 27MU67 – seems to lose sync/picture every other value. So, 858 is fine, 857 gives me a black screen, 856 is fine again, and so on until 800.

[awe444]

Short answer: Yes, use the 240p test suite and manually tune the sample rate for each console then save profiles. The linearity test is useful; also the test suite’s vertical black/white stripes screen (try to make all the stripes equal width).

Longer answer:

The reason a sample rate of 858 was giving you a 3:2 aspect instead of 4:3 is because the OSSC’s line-doubled-240p output is digital 480p = 720×480 pixels, which when fully filled is 3:2 aspect. By changing the sample rate to 800 you’re putting black bars to either side of the 640×480 image, still inside the 720×480 frame. Different digital displays will display the 720×480 image differently, some may squash it to 4:3, crop it to 4:3, others may display it fully at its actual 3:2 ratio (sounds like what was happening with yours).

If you’re wondering what the numbers 858 and 800 have to do with the line widths of 720 and 640: The total “pixels” in each line of an analog signal equals the active pixels (e.g., normally something between 320 and 256 per line for a console intended to be viewed at 4:3) plus the back & front porch pixels, plus the sync pulse pixels. Together these normally add to around 400, which when doubled is the 800 sample rate at which the OSSC is set.

Changing the sample rate does seem to alter the sync parameters of the output 480p signal; and as you already noted with your display’s lost signal for odd-number sample rates, different displays will vary with their compatibility of said signal. So while you’re best bet is indeed to use the 240p test suite to tune each console’s width to your liking, there’s no guarantee your display will be compatible with the optimal width.

There’s an “optimal timings” chart on the OSSC wiki that is very easy to miss:

http://junkerhq.net/xrgb/index.php/Optimal_timings

On that page you’ll find timings for N64, Saturn, PS1, DC, and a couple arcade boards. Personally I have not been able to successfully get the N64 and Saturn sample rates of 387 and 427 to work on my setup, though I’ve only tested on one TV so far.

[Galdelico]

That’s great, thank you.

Yeah, my monitor only comes with ‘widescreen’, ‘original’ and ‘1:1’ screen ratio options. I guess what I’m getting in Linedouble – with the monitor set to ‘original’ – are the filled 3:2 you mentioned (without any vertical mask to cover the colored overscan of most MD games, you can clearly see the frame touching the top and the bottom of the screen, as well as the v-mask starting to crop from the very first/last line, once again at the top and bottom of the screen respectively).

I’ll be able to set at least the MD, since the Mega-CD is the only console I can boot up the suite with no need of modifications… With other systems – the Saturn, the Playstation 2, the original XBOX and the GameCube, all unmodded and unable to read CDRs – it may be a bit trickier, if not impossible, to get it run. Are there values to use (at least) as a starting point?

— Edit — Since I’m now getting very subtle jittering, during horizontal scrolling (it’s not wide-spread all over the screen, but localized around fine details, such as the tips of the green palmtrees on blue background, in Sonic 1), I wonder if there’s something else to tweak, in order to perfectly stabilize the image again, as it was before touching the H samplerate.

Thanks so much once more. ^_-

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