Dreamcast S-video vs. VGA (BBS Gekko)
17I recently ordered the Gekko VGA box from the Behar Bros., and wanted to compare the video quality against the generic S-video cables I was using with my Dreamcast. The result was... complicated.
00:00 Boot
00:21 Pre-rendered cutscene
02:17 Title screen
02:32 In-engine cutscene 1
03:50 Gameplay 1
04:31 In-engine cutscene 2
05:43 Gameplay 2
***
Resolution & aspect ratio:
While the VGA enables progressive scan, taking the resolution from 480i to 480p, this came with some complications. When I first hooked up the Gekko, the image I got was squashed horizontally. It showed up as roughly 600 x 480, rather than 640 x 480.
After some head-scratching and research, I discovered that there's a quirk in the way Dreamcast outputs VGA: it produces an image that's 720 x 480, with letterboxing (black pillars) at the left and right around an image 640 pixels wide. Most modern TVs and capture cards see an image that's 480 high, and assume it's 640 wide, and then squash the 720 down to 640.
Sources:
https://junkerhq.net/xrgb/index.php?title=Dreamcast#Dreamcast_aspect_ratio_peculiarities
https://en.m.wikipedia.org/wiki/Dreamcast_VGA#Functionality
This isn't a bug with the BBS Gekko, it's a quirk of the Dreamcast. To compensate, I unlocked the aspect ratio in OBS and horizontally stretched the video capture until the aspect ratio was correct. This doesn't distort the image, because the squashing was per-pixel, so I'm just taking rectangular pixels and stretching them until they're square.
If there was some way for the Gekko to compensate, like an option switch to output a 640x480p signal, with the letterboxing cropped out, I could recommend the Gekko without reservation. As it is, if you just want to play on a TV with no fuss, I have to recommend sticking with S-video, where the cable is plug-and-play.
(I think this issue may be related to the right-side cutoff problem Adam Koralik saw with this device in his video. See: https://www.youtube.com/watch?v=bwgICMikfB8&t=694s)
Advantage: S-video
***
Video quality:
See for yourself, the VGA is sharper and clearer, no question. The S-video also has juddering, some of which is inherent, and some of which is from my capture card de-interlacing.
Advantage: VGA
***
Saturation:
This one is also complicated. At a glance, the S-video produces blacker blacks and whiter whites, for a broader dynamic range. However, especially at the white end, I'm inclined to say it's over-saturated. See, for example, the "PressStartButton" and "Sega Enterprises, Ltd." text on the title screen. In VGA, there's a nice grey outline/shadow, but it's hardly visible in S-video, because the whites are so blown-out.
Advantage: A matter of taste
***
Audio:
What you're hearing in this video is the audio from the S-video cables. Unfortunately, I can't do a side-by-side audio comparison. I wanted to post the S-video audio, because...
If you listen closely at the start of the first in-engine cutscene (Sonic and Amy on the deck), it starts out mono from the right, before stereo audio pops in as the camera pans over the robot. I'm not sure if that's just my cheap S-video cables, or a loose connection, or what.
Audio from the VGA box, however, is rock-solid stereo the whole time.
Advantage: VGA
***
Verdict: For me, the BBS Gekko VGA box is such an improvement in video quality, it's worth it. If there was a switch to compensate for the Dreamcast's 720x480 output, and it had a slightly broader dynamic range, I'd call it perfect.
Hardware setup:
-Sega Dreamcast (NTSC rev 1)
-Generic S-video cables
-BBS Gekko VGA box (https://www.beharbros.com/gekko)
-RetroTink 2x Pro Multiformat upscaler/digitizer (https://www.retrotink.com/product-page/2x-multiformat)
-Elgato HD 60 S+ capture card (https://www.elgato.com/en/game-capture-hd60-s-plus)
#Dreamcast #OriginalHardware
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