New TV - Dreamcast problem

[beetroot bertie]

Just a query about the DC's 60Hz output.

It was perfectly fine on my CRT TV at 60Hz but on my new LCD TV, the 60Hz setting produces slightly wavy/wobbly graphics. You can see everything fine on the 60Hz test screens but there's this slight distortion similar to heat off the roads in summer that makes things a little wavy to look at.

This doesn't happen at 50Hz and I'm using the same official Sega scart cable that I used with the CRT TV. I have a PAL DC.

I can live with this effect as most games I have are 50Hz anyway but it kinda spoils my Japanese import games.

Anyone got any suggestions/hints/explanations?

Ta.

[Christuserloeser]

It's your TVs 100Hz technique I presume - or some other kind of digital image "enhancement". Try to turn off all of this stuff. It's decreasing your TV's picture anyway.

Edit: Actually I am in a similar situation. It isn't as easy as I thought to update my retro gaming collection to HDTV compatibility. I think I will post my findings and thoughts on this later on as some kind of a FAQ/Guide or something.

Edit2: Don't throw away your CRTs people. ^^

[beetroot bertie]

I'm both happy and sad that someone else is in the same boat as me, and look forward to your faq/guide.

If I find any more out, I'll post it too.

I have turned the various "enhancements" off and checked it with the vga box which appears fine, displaying none of the wobblyness. Would I be right thinking that the VGA box outputs at 60Hz anyway?

EDIT: Just had a play around and I've managed to lessen the effect quite a bit by separating the cable from the others behind the TV. I'd previously got them all bunched up round the back in an attempt to keep things tidy. The 360 power pack is also round the back, plus the power lead for my VCR/DVD. I've removed the scart cable from the rest and the wobble is really only very slight now, hardly noticable but still there a bit. I guess it may me down to sheilding in the cable and/or interference from the other cables.

[Christuserloeser]

I have turned the various "enhancements" off and checked it with the vga box which appears fine, displaying none of the wobblyness. Would I be right thinking that the VGA box outputs at 60Hz anyway?

I guess it's your LCD's de-interlacer that's been the reason for the wavy/wobbly graphics you've described. See, the Dreamcast outputs 480i via RGB-SCART/S-VHS where the i stands for Interlaced. LCD and Plasma TVs however are not capable of displaying interlaced signals so they have to de-interlace it first. That could be causing the effect you've described.

Here's more information about Interlace:
http://en.wikipedia.org/wiki/Interlace


The Dreamcast's VGA box outputs true EDTV at 480p60 (Progressive Scan). That's a signal that digital devices like LCD and Plasma can work with much easier.

More info about Progressive Scan:
http://en.wikipedia.org/wiki/Progressive_scan

If you can use the Dreamcast's VGA box than by all means use it.

[beetroot bertie]

Thanks for your help.

I understand what you're saying, but wouldn't the 50Hz mode that works fine also be interlaced? If so, that would wobble too yeah?

[Christuserloeser]

I am sure it's that 100Hz "feature".

I can't turn it off on my Samsung TV. It's always active on all interlaced inputs (RGB-Scart, S-Video and Composite/FBAS). I can only circumvent it via it's progressive scan compatible inputs (in my case that's either Component YPbPr/YCbCr or HDMI).

If you feed your TV a Dreamcast signal via RGB-Scart, then you'll get 576i at 50Hz or 480i at 60Hz. Assuming 50Hz looks so much better than 60Hz on your TV then I am pretty sure it's caused by the lack of 120Hz support (60Hz x2) which my TV doesn't seem to have a problem with.

Some more info about 100Hz/120Hz: http://en.wikipedia.org/wiki/Flicker-free

I assume that your TV is similar to mine in that its 100Hz feature isn't active when feeding it with a progressive scan signal.

50Hz / 60Hz can be both interlaced (576i, 25 fps / 480p, 30 fps) and progressive (576p, 50 fps / 480p 60 fps). The later runs at twice the frame rate and resolution thus there isn't any reason to apply a 100Hz/120Hz filter.

If you use the Dreamcast's VGA box you'll always have 480p at 60Hz - no matter which game you will play! Even the European PAL version of Sega Rally 2, which lacks any 60Hz option and just runs 20% slower than the US/JP NTSC original, will run at full 480p60.