Darryl Hock's

Aurora Multi-Standards Converter

In principle, a scan converter is simple - an electronic "box" with video going in at one standard or format and coming out at another. Having designed and built a few in my time, they are a challenge to build and a challenge to set up. Until recently, the only scan converter for NBTV was designed by Peter Smith in the UK. Variations on Peter's unit provided much of the video for the famous NBTV CD releases from the Narrowband Television Association. I definitely wanted a scan converter to produce real-time NBTV programming, but I didn't relish getting all the parts for Peter's unit, let alone designing and building my own. Much to my delight, Darryl Hock (converter@comcast.net) was responding to the needs of television collectors (electronic and mechanical) with the design of a multi-mode (= multi-standard) unit that converts NTSC or PAL video to a wide range of electronic and mechanical formats. Physically, the unit is incredibly compact - a little larger than a pack of cards.

The front panel (top of the pair) is ultra-simple, with a POWER switch to the right and a STATUS/LOCK LED on the left. The rear apron, from left to right, features a 6VDC power jack, composite (PAL or NTSC) video input, S-video input, video output, audio input, audio output, and the 15-position MODE switch.

You will already have noted the lack of panel labels, but this is not a problem as the bottom of the unit has a chart with labels and functions that cover most routine operations!

The circuit board is populated by a number of Very Large Scale Integrated (VLSI) circuits and a small DIP switch which is used to set some parameters (NTSC vs. PAL input, for example). In terms of the output modes, it depends in part on whether an NTSC or PAL signal is applied at the input:

This listing includes only the most basic mechanical modes. There are a total of 15 output formats with both PAL and NTSC input - lots of early electronic modes and a few higher-resolution mechanical modes as well. The mechanical modes in common to both NTSC and PAL input are the popular NBTV Association 32-line/12.5 fps, and the Baird and TeKaDe 30-line/12.5 fps systems. With respect to the 32-line NBTVA standard (I haven't checked the others), there are some issues with NTSC input that you should be aware of. The first involves timing corrections:

Both images of our friend Bugs were displayed and grabbed from Gary Millard's "Big Picture" program. Take a careful look at the bottom edge of both images. On the NTSC image you will see periodic little offsets as the software and hardware converts from a 60 Hz format (NTSC) to a format that was basically derived from a 50 Hz power line standard. It isn't easy and the constant on-the-fly conversions lead to the very slightly jagged lower edge. While it doesn't amount to much in this single frame capture, the result is a faint, moving vertical bar-like pattern that is a bit annoying. With PAL input, continuous corrections are not required, the lower edge is straight, and there is no vertical pattern!

The second issue with NTSC input is that the final signal has a very slight timing error 399.4 Hz frame rate instead of the ideal 400 Hz. . This is not an issue with synchronized televisors, which can alter their line/frame rate to "lock" on the signal, but will prevent display on systems that rely on synchronous motors or synchronous software. That's why I displayed both images using Gary's software, since the NTSC image will not sync on my "Virtual Televisor" system! For the ultimate in standard compatibility, I would suggest that one simply get a PAL format video source for the 12.5 fps modes. Most of the places that sell small security cameras can provide PAL-standard units at no extra cost.

Here are a few examples of images captured from a PAL source. As is quite common with NBTV pictures, the human brain is programmed to do an excellent job in sorting faces and, as a result, portrait shots usually work quite well. In contrast, the image at the lower right doesn't work as well. It is a cartoon frog that I thought would make a nice picture, but it is too "busy" with the small dark spots and it is not a familiar shape. All-in-all, not a good combination.

If you are mentally comparing these pictures with some of the other NBTV images on this site, you may conclude that the standards converter is producing images that are distinctly "softer" than some of the others you have seen. In a way this is true, but matters have to be put into perspective:

(A) is an image from my ROMScanner, captured using my Virtual Televisor. All in all, a very good example of a 32-line NBTV image. (B) is the same ROMScanner image, but captured with Gary Millard's Big Picture software. The image save function on this program seems to automatically introduce some of the anti-aliasing elements that you can select for display. The result is a reduction in the coarse line structuring, resulting in a smoother/softer image. Whether A or B is the better image is a matter of taste - they are both quite good. (C) is the same picture, but generated via the Aurora standards converter and captured with the Big Picture. It is even softer than B, but at least part of that is because old bugs is a bit smaller than in the previous examples. I think both the conversion from video and the capture software contribute to a slightly softer display, but it is something you would not notice as much if you were viewing full-motion video, which is what the standards converter is all about.

OPTIONS

The Aurora Multi-Standards Converter is a dynamite unit for any serious TV collector. Presently (Jan 2008) the unit is out of stock and you would have to contact Darryl (converter@comcast.net) to see if and when the units might be available. Fortunately, if you are interested primarily in the 32-line NBTVA or 30-line Baird standard, Darryl Makes an Aurora Standards Converter Model SC which will generate either of these modes from either NTSC or PAL input. These units are in-stock at a cost of just $225.

Ralph E. Taggart (taggart@msu.edu)