Soft15kHz 51 Hz mode

[FoxMontage]

Hello all,
I've recently managed to get a D.I.Y. VGA to SCART cable working to hook up my Radeon HD3650 to my Sony Trinitron using Soft15kHz.

My question is in regards to PAL resolutions (anything x 288 progressive). When I choose these, both CCC and Speccy report the refresh rate as 51 Hz. I know this isn't necessarily an accurate figure, however I am noticing a "judder" a little over once per second in various SNES/Mega Drive emulators. The drop shadow test in the 240p test suite (PAL version) does not render correctly either. I'm guessing that this is due to a mismatch between the game running at 50 Hz and the screen refreshing at 51 Hz

I'm just wondering why exactly Soft15kHz runs these resolutions at 51 Hz as opposed to 50. If anyone has any experience with this, or has been able to find a work around I would appreciate any advice.

Unfortunately, I am very nostalgic about the quirks of classic PAL gaming (slower games, 8:5 aspect squish etc.) but I also love to fiddle with things to see how they work.

For those interested, I enable composite sync in version 12.1 (8.93-111205a-132226E-ATI) Catalyst Control Centre (+Horizontal / -Vertical) which I take from pin 13 on the VGA and feed to SCART pin 20 via a 420 Ohm Resistor. I couldn't find anything online to verify, but since this works, I'm guessing that this composite sync signal is TTL ((5 V)/(420+75))*75 =~ 0.7V. I did read somewhere that said composite sync should be nominal 1 V into a 75 Ohm termination so perhaps this is a bit low. Maybe someone could give me some insight on this?

Thanks,
Fox

[buttersoft]

Not a direct answer, but if you're on Win7 the newer/newest build of crt_emudriver supports c-sync, or rather VMM does, so you could just switch over and have more control of everything. I mention this as i've had the same problem you are when defining my own modelines through more cumbersome methods, but never using crt_emudriver.

[FoxMontage]

Thanks Butter,
I'm on Windows 7 32-bit at the moment, but I'll install 64-bit and give that a try.

Does anyone know a good resource for learning the basics of analogue video signalling? I'm looking to get my head around what all of the timings mean and what they correspond to i.e. front porch, back porch, sync timings etc.

Cheers,
Fox

[Xer Xian]

Does anyone know a good resource for learning the basics of analogue video signalling? I'm looking to get my head around what all of the timings mean and what they correspond to i.e. front porch, back porch, sync timings etc.

You can start from this voice on wikipedia: https://en.wikipedia.org/wiki/Raster_scan

If you want an in-depth analysis, you can google 'Video Demystified'.

Also here you can find a well-made video about CRTs tech in general: https://www.youtube.com/watch?v=l4UgZBs7ZGo

[FoxMontage]

Thanks for the links Xer Xian.

I was able to get a refresh rate closer to 50 Hz (50.08) (15625 Hz horizontal) using a tool called winmodelines. This tool allows you to edit existing modelines. Everything runs smoothly now.

I wasn't able to get crt_emudriver working, even on 64 bit windows as it appears my HD 3650 is unupported.

I also found a lot of interesting information here regarding the anatomy of analogue resolution if anyone is interested.

Thanks, Fox.