Add S-video for clearer video

A short history of S-video: In the beginning TV's were black and white. They just received a luminance signal (luma: how bright something is) Then people wanted color. But how to add color and still have all the old black and white TV's still work? The answer was to introduce a chrominance (chroma) signal along side the luma signal. The black and white TV's still get the luma signal and the color TV's will receive both. Hence we get what we now call composite video. If you look the word composite up in the dictionary you would see that it means you are blending several things together. Unfortunatly, the composite signal tends to be a bit blurry. So Commodore decided on the C64 to seperate the luma and chroma signals. They called it LCA back then and it worked by having two seperate RCA jacks. Later in the 90's the S-Video (stands for seperated-video) connectors started to become popular. The picture is clearer because the signals are being carried on seperate wires.

It is possible to merge the luma and chroma signal into a single composite signal with a very easy design, as you can see on the left. Basically both grounds go straight through. The luma signal goes straight to the tip of the RCA jack. The Chroma signal also goes to the tip, but passes through a capacitor first. I didn't have a 470pf available, but I used a 580pf and it worked fine. Guess what? You already have this circuit built into your DTV unit. So the easiest way to get an S-video signal out of it is to remove the capacitor which links the two signals together.

This is the video circuit in the DTV (specifically the Hummer) and I have anotated the picture with instructions.

You don't have to take the luma signal from that little pad. Once you remove the capacitor the regular video output that goes to the original cable is now turned into the luma signal. If you plugged it in just like that, your picture would now be in black and white.

Now there are two ways of adding this to your system. One way is by creating an S-video connector on your DTV. But if you do this, you will sacrifice having a composite signal. You can create a cable (see above) to convert S-video into composite so you will still have that option. (This is the approach I took) Or you could create some kind of toggle switch that you could take the capacitor in and out of the loop which would allow you to have both composite and svideo on the same unit.

Here is a screenshot of BASIC (the POKE statements have no significance to this) using the S-Video connector into my video capture card. Notice (when you click to enlarge) that you can see every pixel and it is very sharp.

Here is another example for you. This one from the game Atomino.

A Side-by-side comparison using a blown up image from Thrust Concert.
This is a side-by-side comparison. You'll have to click to expand this image to see the effect. The image on the left is S-Video and on the right is Composite. I took these two screen captures within seconds of each other and nothing at all was changed other than the cable I used. I have not doctored either of these pictures in a paint program other than to crop the pictures and expand them so you can see upclose. First I'll mention that the DTV outputs pretty good and clear composite video compared to most things. But you can still see some difference. Not only is the color saturation better on the S-video, but look next to the poles on the drumstands for the composite version and you'll see picture noise in the black area.

To Sum it all up: This hack isn't for everyone. First of all, it won't work on my 1084 monitor (which doesn't matter, see next paragraph) but works on every TV and video capture card I've tried it on. The results are a mixed bag. On my video capture card the improvement is small, maybe 20% better. On my bedroom's 20-inch television the improvement is dramatic. If I swtich between a composite cable and S-video there is a very noticable difference. However, on a few other televisions I've tried the advantage seems less. I suppose a lot of it has to do with how good the comb-filter (if it even has one) is on the TV's composite input. So your mileage will vary. I would say if you just play the occasional game on your DTV, I wouldn't worry about it. But if you are going to be sitting in front of it writing programs for hours, I'd highly recommend the hack.

The main reason I decided to do the hack is that I'm going to have to retire my Commodore 1084 monitor. It makes a high-pitched whining noise that bothers my wife and she says it has to go. So I'm going to be buying a 13 or 14 inch color TV with S-video input to replace it. I figure a TV isn't going to be as sharp as my 1084 in composite mode so the S-Video will probably make a more significant difference there.


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