Genlock on the C64

When you look-up the word “Genlock” on Google, chances are you’ll find hundreds of websites that talk about this technique and how it worked on systems like the Amiga.

If you’re wondering what this whole “Genlock” business is about, here’s a little background.
On Wikipedia, the definition for Genlock is “GENerator LOCK) is a common technique where the video output of one source, or a specific reference signal from a signal generator, is used to synchronize other television picture sources together. The aim in video applications is to ensure the coincidence of signals in time at a combining or switching point. When video instruments are synchronized in this way, they are said to be genlocked”.

Say you have a two video signals, typically one coming from a camera or VCR and another from a computer system that has produced some cool intro titles, credits and texts that need to be show in an “overlay” on top of the video image. These two parts need to mixed… easier said than done, as the problem is that the computer screen is different than that of the video screen: A television screen has 625 lines, whereas the analog output of say the C64 caters for 624 lines.
A Genlock device will make sure that both images, those of the TV and computer are synchronized. Depending on the type of device, various techniques are used that perform this trick, but that’s a whole different story all together.

Now, as mentioned above, the Amiga was a true masterpiece when it came to “genlocking” but what’s little known is that it was also possible to do this on the Commodore 64.
That’s right, the good old breadbox was capable of mixing multiple video sources and creating some cool effects.

In 1993 Scanntronik released the “Digital-Genlock” for the C64, a robust piece of hardware that consisted internally of 2 main boards.  One handled all the digital imaging, being the input signal from the C64 and did the mixing of the C64 images into the video image.
The second one was the analog part, where the composite digital image was converted into an analog signal that could then be recorded on a video recorder.

The Genlock was accomplished in the device by storing the C64’s image in memory. When the analog signal from the camera arrived, Scanntronik’s Genlock placed the C64’s image dot per dot on the video image and hence “synchronized” or “genlocked” both video inputs.

To create the fancy intro titles etc. you could use the accompanying software “MiniGen” or use other commercially available titles like “Videofox”.
The texts created in these programs could be made up out of 5 colors (4 colors and “transparent-black”, the latter used to have the video image show up in the parts where the computer image is black, i.e. when used to have texts float over the video image).

All-in-all a nice package, that would have set you back about 400 Euro 20 years ago. Not cheap, but you’d have basically the only commercially available Genlock system for the C64, and that in itself is pretty cool!

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