Sunday, September 11, 2016

RGB Video And Old Game Consoles




The connection between an old game console and a television is kind of like a game of Pictionary being played between the two: The game console is doing its damnedest to describe what it has in mind to the television, and the TV is doing its best to interpret what it's being told. But somewhere along the line, communication breaks down. RF connections are like playing with a drunk person over a particularly crappy cell phone connection. Composite video at least get rid of the phone, but the console is still clearly sloshed. S-video sobers the console up, but hey, the TV still doesn't quite get that the console is trying to draw 'dignity' here. (After all, it didn't go to Gudger College) But there's one last option, and it's akin to the console just screaming the answer to the whole room. That option is called RGB video!

Generally speaking, RGB stands for red, green and blue, the three primary colors of light that, when mixed together at varying intensities, create all of the colors we can perceive. In video signaling, an RGB connection has at least one discrete channel per color.  RGB connections electrically isolate the red, green and blue intensity signals in order to keep them as pristine as possible, which gives them a huge advantage over composite and s-video in terms of image quality. Typically, it also includes one more discrete signal, called sync, which the display uses to figure out which line on the screen it should be updating at a given moment. In old CRT displays, sync is used to aim the electron guns at the correct spot on the screen, while the RGB intensity signals tell it what color and how bright the spot should be. The frequencies at which the the sync signal operates define the resolution of the display; higher frequencies produce higher resolutions. All of the consoles we're working with output a horizontal sync frequency of 15 kHz. That's an important number to remember, as it will come into play later in the discussion.

In an effort to reduce both the bandwidth and the number of physical wires required to carry a video signal to a television, old game consoles smushed their raw RGB data down into composite, s-video, or RF, shaving off a whole lot of image detail in the process. Fortunately, the general suckiness of the resulting video signal wasn't entirely disregarded by the folks who designed these old consoles. Many of them, particularly consoles from the 16-bit era on, actually carry RGB signals right to their external AV connections, making connecting them up to a compatible display a relative snap. The following is a list of all the game consoles I'm aware of which support RGB without any special modifications:


Console Display Resolution Notes
Atari Jaguar 240p
Neo Geo AES/CD/CDZ 240p Audio from AV port is mono only
Nintendo Gamecube 240p, 480i, 480p PAL units only. NTSC model DOL-001
GCs support component video
Nintendo SNES/
Super Famicom
model 1
240p
Sega Dreamcast 240p, 480i Also supports VGA @ 480p
Sega Genesis/Mega
Drive model 1
240p Audio from AV port is mono only
Sega Genesis/Mega
Drive model 2,
model 3, CDX & 32x
240p
Sega Master
System model 1
240p AV port pinouts identical
to model 1 Genesis
Sega Saturn 240p
Sony PS1 240p, 480i
Sony PS2 240p, 480i, 480p Supports component
video natively

Many more game consoles can be modded to output RGB, but that's beyond the scope of this article. The website retrorgb.com has a great deal of excellent information on the subject, including detailed how-to instructions for nearly every game console.

The Sega Dreamcast supports VGA in addition to RGB, and it's the method I recommend for best results. As VGA is an even higher-quality RGB video standard, the Dreamcast looks spectacular when connected to a VGA-compatible monitor or HDTV. Not all Dreamcast games support VGA, though; the ones that do have 'VGA cord' printed on the back of the jewel case.


Getting RGB to your TV or monitor

Connecting RGB may be as simple as plugging in a cable or as complex as building one, depending on your circumstances and goals. I'll cover a few common situations here:

A female SCART connector
Connect directly to a SCART-capable TV: Many European countries adopted a very nifty standard for connecting video devices together in the late 70s, called SCART. SCART, a French acronym for Radio and Television Receiver Manufacturers' Association, is a standard for a 21-pin plug capable of carrying several different types of analog video signals, including RGB. It also carries stereo audio, simplifying the process of connecting up a game console down to attaching one single cable. SCART has been largely supplanted by HDMI these days, but if you still own a television with a SCART connector, you just need to purchase the appropriate cable for your console. Again, retrorgb.com is a great source for these cables, and they can also be found on eBay. Be advised that PAL consoles may require different AV cables from their NTSC counterparts. When in doubt, contact the seller.

Convert RGB to component: If you live in the US, you're unlikely to own a SCART-capable TV. Instead, you might own a TV with component inputs. Component video connectors started appearing on US televisions in the late 90s, as a means of transmitting better-quality video from a DVD player. In the early days of HD television, component cables were also used to connect HDTVs to HD sources. With their red, green and blue RCA plugs, they look like RGB connections, but in fact, they're not. The green cable actually carries luma (the B&W portion of the image) and sync together, while the red & blue cables carry the difference between red & luma and blue & luma, respectively. The TV uses luma along with the red & blue difference signals to internally calculate what portions of the image should be green. In theory, component connections shouldn't look quite as good as RGB, since some of the signals are multiplexed together. In practice, though, the difference is imperceptible.

In order to use RGB with a component-equipped TV, you need to first convert the signal. SCART comes in handy here too, as RGB SCART-to-component converters are widely available and fairly cheap. The one I own is a model CVS287, purchased off eBay for about $50 shipped. The CVS287 has no audio out jacks, so you'll need to either purchase the SC-890-AV audio breakout box or, if you're handy with a soldering iron, attach audio connections directly to the SCART input plug.

When my CVS287 first showed up, its output was tinted green. A quick Google search revealed that these suckers often ship mis-calibrated, and need to be adjusted by rotating one or more of the little dials inside the unit. If you need to make adjustments, make sure to mark your starting point on each dial before you turn it, so you can go back if the image starts looking worse.

One last gotcha concerning this method: As indicated in the table above, most of these game consoles output a really low display resolution of 240p. An old, standard-def CRT TV equipped with component inputs should handle 240p just fine, but an HDTV may not. Of all the HDTVs I've tried it on, only a 2011-vintage Panasonic plasma TV would accept a 240p signal via its component input. If you're unlucky enough to own an HDTV without 240p support, the next couple of options will be your best bet.


Convert RGB to HDMI: Once again, SCART comes to the rescue: SCART RGB-to-HDMI converters are just as common and just as cheap as SCART-to-component converters. The unit I own came from Amazon, again costing about $50 shipped. There's no model number to be found on it, but the Amazon ID number is B00MUNIVRO. It accepts a SCART RGB input (and only RGB; it doesn't support composite video) and converts it to a digital HDMI signal at one of several selectable output resolutions. Unlike the CVS287, this converter works with audio, too. It can send stereo audio from the SCART port through HDMI to your TV, as well as output it to a headphone-style analog jack, and a digital S/PDIF coax jack. 

The converter I have works great with source resolution from 240p on up, but it does have a couple of annoying problems. First, there's no documentation included at all. It's fairly foolproof to set up & use, but for the button that switches output resolution. It may be labeled "720p/1080p", but it doesn't just toggle between those two resolutions. Pressing it once brings up the converter's on-screen display. Pressing it again in quick succession cycles through several output resolutions, including a few oddballs which may not be supported by your HDTV. If you plug this sucker in & get an error from your television about an invalid signal, try pressing the 720p/1080p button once every couple of seconds until it returns to a supported resolution. 

Its other, bigger problem is that it introduces a brief but noticeable lag to the outputted video. From what I've been able to tell, the lag is about about 2-3 frames long, or roughly 1/30th of a second. That doesn't sound like much, but it can make games that require absolutely perfect timing much more difficult to play. HDTVs themselves introduce a fraction of a second of additional lag, so bear that in mind too. If you go this route, I recommend enabling your TV's 'game' mode to minimize any additional lag.  I only have personal experience with this one make of HDMI converter, but others on the Internet have reported that most HDMI converters like this introduce a similar amount of lag. One notable exception is the Micomsoft XRGB-Mini. It inserts only about 1 frame of lag, but it'll set you back a cool $375, plus shipping from Japan.

NOTE: Japan used a very similar-looking connector, called JP-21. However, it is not directly compatible with SCART! Do not connect a SCART cable to a JP-21 device, such as the XRGB-Mini, without using a converter cable, like this one.


Use a VGA scaler: As I mentioned earlier, VGA is a very high-quality analog video standard, and it's an excellent option if your TV or monitor supports it. To maintain the best image quality possible, it uses five signal lines instead of four; one line each for red, green and blue intensities, plus separate horizontal and vertical sync lines. It also uses higher sync frequencies in order to achieve resolutions greater than 240p or 480i. To use VGA with anything other than the Dreamcast, though, you need a device called a scaler or a scan converter. At the very least, the scaler needs to accept an RGB+S (S in this case stands for composite sync) signal at the lower sync frequency of 15kHz and spit out a RGB+HV signal at sync frequencies high enough to drive a VGA monitor. (31kHz or greater) Additional features include the ability to de-interlace the source signal, (Convert a 480i source to 480p.) overlay fake scan lines, and output multiple resolutions. 

Gonbes GBS8200
The scaler I own, a Gonbes GBS8200 is a pretty bare-bones unit. It doesn't insert scan lines, and the quality of its deinterlacing isn't all that great. It doesn't even have a case, as it's intended to be mounted inside an arcade machine's cabinet. Still, it's dirt-cheap and it supports a wide variety of input sources: It accepts CGA, EGA, (Two very old IBM PC video standards) component and 15kHz RGB+S, and it outputs a de-interlaced VGA signal at a number of different selectable resolutions. Unlike the other solutions I've talked about so far, this one doesn't rely on SCART, so you are going to have to build your own AV cables in order to use it. 

If you choose to go down this route, you'll probably want to look into a scaler that can accept composite video as its sync source. Most of the above game consoles don't have a separate sync line; they use their composite video output as a substitute. Composite video contains sync, but it also contains a lot of other garbage that some scalers don't know how to strip away, leading to scrambled video. If your scaler displays garbage or complains about 'no sync' when it's fed composite video as sync, a device called a Sync Strike, or a similar board with the LM1881 chip can strip out the extraneous noise, leaving a clean, usable sync signal.


Use an RGB monitor: Until now, I've focused on converting our consoles' RGB output into a format that more modern displays can work with. The last option I'm going to discuss is connecting a console to what it was intended to use from the start: A good, old-fashioned 15 kHz RGB monitor. Several early home computers, like the Commodore Amiga, the Atari ST, and the Apple IIGS used 15 kHz RGB monitors, or at least supported them in addition to conventional composite monitors. A handful of early-generation VGA monitors also support 15 kHz. If you happen across any monitor on this list, there's a fairly good chance it'll work with your game console. Avoid any monitor that has a single input labeled 'digital ' or 'TTL'. While technically RGB, these types use a digital signal which is incompatible with any retro game console you're likely to own. Likewise, steer clear of any CGA or EGA monitor unless it specifically has an option for analog RGB.

Commercial 15kHz RGB monitors were also commonly used in closed-circuit setups, in hospitals as endoscope displays, and in television production studios. Commercial monitors usually have the added benefit of looking very good, since an accurate, distortion-free image is a must, whether you're videotaping a soap opera or the inside of someone's colon. Some of the best standard-def CRT displays ever made are members of the Sony PVM and BVM family of professional monitors. These units sold for of thousands or even tens of thousands of dollars new, so even used, they can be a bit pricey. Most arcade monitors, particularly JAMMA-compliant ones, operate at 15 kHz too, but arcade boards usually output a higher voltage to their displays than do home consoles. An arcade monitor connected directly to a home console would probably show a very dim image.
Sony PVM-14M2U (left) & Commodore 1080 (right)
If you find a compatible RGB monitor, you now need a way to connect it up. Commercial monitors typically use individual BNC jacks for each signal line, and several websites, like these guys, sell a cable with a female SCART jack on one end, and individual BNC connections for video on the other, as well as RCA connections for audio. You attach your specific console's AV-to-SCART cable to to it, and then it to the monitor.

The Sony PVM monitor (top) uses separate BNC connectors for R, G, B & sync.
The Commodore monitor (bottom) condenses R, G, B & sync connections into a 9-pin D-sub connector

The consumer-grade RGB monitors that old computers used are a little more complicated to work with. Since each manufacturer used its own pinouts & connector styles, you may need to build your own cable to connect it to your console of choice. In either case, expect your RGB monitor to be much less tolerant of garbage on the sync line, so try to use a clean sync signal with it, either directly from the console or with a Sync Strike.

Note: Not all monitors in Sony's PVM series have RGB inputs, so be sure to do your homework before buying one. Also, you need a monitor with an external sync input. Avoid monitors with only "internal sync", also called "sync-on-green."

Left: A Super NES-to-SCART cable and a SCART-to-BNC cable with on-board Sync Strike chip.
Right: A home-made SCART-to-Commodore cable, also with on-board Sync Strike chip.



RGB Compared


In this first batch of pictures, I'm using a Sony PVM 20m2u monitor. In addition to having an excellent picture for a CRT, it sports composite video and s-video connections in addition to RGB. The SNES supports all three standards as well, so it'll be our source. Apologies for the dark horizontal bar visible in some of these pictures; it's what happens some times when you photograph a CRT.

 First up is composite video:




Colors bleed into each other in several places, including the coin counter, the red turtle shell, and the front of Bullet Bill. In addition, a checkerboard pattern, called dot crawl, is visible in the smiling clouds, the timer, and the score counter. Definitely room for improvement here.


Now let's check out s-video:




S-video represents a pretty significant bump in image quality. The dot crawl is gone and the colors don't bleed together to nearly the same degree as they did with composite video. The image is also slightly brighter, too. However, sharp borders between light and dark colors, such as the clouds' eyes and Bullet Bill's face against the white background smear together to some extent, causing a slight loss of definition. On solid colors, like the blue sky, a slight checkerboard pattern is visible, too. 

OK, so let's see RGB finally:




The jump in image quality isn't quite as dramatic as moving from composite to s-video, but it's still impressive. The colors are much richer and more saturated, each individual pixel is clearly-defined, and there is almost no fringing, smearing or bleeding. The only image flaw I noticed is a slight horizontal bleed from the black border around the 'mario' text onto the blue pixels just to the right. 


Next up is a modern HDTV, a Samsung UN48H6350 48" LCD unit. Like most modern HDTVs, it has no s-video input, so I will only be comparing composite video fed directly from the SNES to the RGB-HDMI converter. In both cases, the TV is in game mode. 

First up is the composite video:





This TV has surprisingly good standard-def image processing. There's no dot crawl, and in most cases, the pixels appear sharp. A notable exception is Mario himself, who is a muddy blob, and the clouds' smiles, which lack definition.

Now for the HDMI converter:




Unsurprisingly, it looks excellent by comparison. The pixels are sharp and the colors are nicely saturated. It is almost indistinguishable from the image you might get from an emulator. Again, the only notable image flaw is the same ever-so-slight horizontal bleed from 'mario.' 


As I mentioned earlier, input lag is an issue with pretty much all HDTVs. (It also happens to be the reason why light gun peripherals, like the Nintendo Zapper, no longer work.) Generally speaking, the more devices in the signal path, the laggier things get, and my experience with the converter vs the TV's own composite connection bears this out. To demonstrate input lag, I split the output from the SNES, sending it to the HDTV and a reference CRT monitor at the same time. In this first video, the HDTV is connected via composite video:




The lag is certainly detectable, but at least with Super Mario World, it didn't cause me too much difficulty. 

This next video shows the HDMI converter:




The lag is much more apparent here, and this time, it did interfere with my ability to effectively time some jumps. I personally would not play a game like SMW using this converter, despite the impressive bump in image quality.

Input lag is hard to pin down. It can vary wildly from manufacturer to manufacturer and even from model to model. It's often not advertised too, since it has generally trended upward as HDTVs have gotten more sophisticated. Fortunately, TV review sites like this one include input lag in their evaluations. I wouldn't recommend buying a new TV just because it has the lowest lag times, but if you plan to use it as a display for any type of game console, old or new, and what you enjoy playing requires the reflexes of a spazzy 8-year-old, it should be a consideration. One of those low-lag HDTVs paired with an XRGB-mini converter might well be the key to retro gaming bliss, in lieu of a CRT display.


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