Extron RGB interfaces – An overview

Since I published the article on using the Extron RGB interfaces with the DVDO Edge, I’ve been asked by several people about the capabilities of the Extron units in general. There still seems to be some confusion as to what these units do and what they don’t do. In this article, I’ll break down the various capabilities of the different models, hopefully clearing up the confusion somewhat.

Just what is an Extron RGB interface and what is it for?

The Extron RGB interfaces are designed for use primarily in business and education. The general idea is that you have a big-screen projector display in your boardroom or lecture theatre. Your lecturer or presenter then comes in and rather than having to fiddle around the back of said screen, he/she can simply plug in their laptop or other computer into the Extron RGB interface, which can then in turn be permanently connected to the display by a discretely tucked-away cable. On longer cable runs, the Extron can also boost the signal. The devices also contain some clever signal processing to improve compatibility, but they aren’t to be considered full-blown video processors. While designed for 31khz video, The Extron interfaces are compatible with both 15khz and 31khz signals, as long as you can find a suitable cable.

For the videogame enthusiast

It’s an unfortunate truth that, in order to enjoy many videogames exactly as the original programmers intended, the only option is to run the original hardware. While emulation based solutions do an important job preserving classic games, they are still an approximation of the original experience. Of course, as TV designs change and time goes by, less emphasis is placed on the processing of older analogue signals. Because of this, it gets harder to run classic hardware on modern displays without encountering incompatibilities. In some cases the Extron RGB interfaces can help with these incompatibilities. Read on for a run-down of the features and what they might be useful for.

Sync processing – This is the feature that originally got people interested in the Extron units. The Extron RGB interfaces include various sync processing features. All of the Extron units have a switch that toggles between ADSP and DDSP. ADSP stands for “Advanced Digital Sync Processing” and DDSP stands for “Digital Display Sync Processing” (not disable digital sync processing, as I have erroneously stated in the past). ADSP not only improves compatibility with some displays, but on certain Extron units it allows the picture to be manually centred, both horizontally and vertically. Unfortunately ADSP doesn’t work with all display equipment (ADSP has poor compatibility with the DVDO Edge, for instance), so DDSP mode is included as a fall-back.

Sync splitting/joining – Feed the Extron a video signal with horizontal and vertical sync and you can output a composite (combined) sync signal. Feed in a composite sync signal and you can output a RGBHV (separate sync) signal. This is useful when working with the DVDO Edge videoprocessor, for instance, as it improves compatibility. You can also use it with the XRGB Mini to connect VGA signals, e.g. from a Dreamcast or retro PC.

Sync polarity changing – In some instances, particularly when dealing with the SLG3000 scanline generator, it is necessary to change the polarity of the sync signal in your chain. Some Extron units have a “NEG SYNC” switch, others have an internal jumper. Either way, you can change the polarity of the signal and fix incompatibilities.

Sync type changing – If you’ve ever tried to play a 480p game from the PS2 in RGB mode (rather than component video mode) chances are all you saw was an oddly colored mess on your screen. The reason for this is that the PS2 uses sync on green, or RGsB, rather than the more common RGBHV, when outputting 480p in RGB mode. If you need to convert between RGsB and RGBHV or RGBC, the Extron RGB interfaces can do that too.

Centering – Horizontal and vertical picture shift is quite common with RGB sources. On certain models of Extron interface (e.g the 203 Rxi) you can correct for this by using the centering controls on the front of the unit. This only works if ADSP is enabled.

Level/Peak control – These controls are typically for longer cable runs, you can use them to boost or tweak the voltage and brightness. They are useful in some instances for reducing ghosting on an image.

480i to 240p conversion – Want to play those Xbox 360 arcade classics in true 240p on your CRT, rather than crappy 480i? By connecting the RGB output through the Extron interface and setting the DDSP dip switch to on, the interface does a quick conversion from 480i to 240p. For more details of how this works, see this page (near the bottom). Note this technique only works with CRT displays, it cannot be used to trick a video processor into processing 480i content as 240p.

Frequently asked questions

Do the interfaces add any input lag? – No, the devices do not have a frame buffer so no input lag is added.

How do I connect SCART cables? – Use a Sync Strike or a cable such as this one. You must use a clean/raw sync signal, the interface will not accept composite video for sync. If you’re making your own cable, connect composite sync to the horizontal sync input (pin 13 on the VGA connector).

How do I connect the output to my XRGB or the TVs SCART input? –  A cable such as this one will work for the XRGB3 or XRGB Mini. The cable will work on many TVs too, but remember it does not supply the signal voltage on pin 7. Some TVs require this to be present or they will not switch to RGB mode. In this case you will need to use something like the Arcadeforge UMSA and a BNC to VGA cable.

What resolutions are supported? – Pretty much anything that can be sent down an RGB cable. Interlaced modes are the only resolutions that can cause issues. As a workaround, turning the DDSP switch on typically resolves any problems (though this stops the picture centering controls from working).

Conclusions

Not everyone will need an Extron RGB interface in their setup. For those who do need one of their specific features however, they can usually be purchased very cheaply on E-bay. I recently sold one on auction and it went for just £10 plus shipping. Probably the most desirable unit is the 203 Rxi, which includes a three way VGA switch and the full set of centering and level/peak adjustment controls. Although this unit does place the DIP switches at the back, which can be inconvenient if you want to toggle between ADSP and DDSP modes.

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