HDTV Zine

One problem is a light snow that sometimes shows up in HD broadcasts of SD material. This is a consequence of the change in the bandwidth between recording and playback. Although the bandwidth of SD is said to be 4 MHz, it is not a sharp cutoff. The roll-off starts before 4 MHz, but some image information above 4 MHz survives the recording process, albeit mixed with electrical noise (snow). The broadcaster has to decide if he wants to filter it out. If the broadcaster decides to filter out the snow, some image information is lost also, resulting in increased blurriness. Some people would prefer the snow to the blurriness, but others might not.

There has been a significant improvement in the average quality of NTSC broadcasts over the last three years. There are two reasons:

First, 640×480 used to be a target that TV production crews believed they had to aim for but didn’t really have to meet. Their product was often well below 640×480, for a variety of reasons. But now, with large high-def sets becoming common, these production people are seeing how bad their product can look, and are paying more attention to the details (camera focus, circuit noise, cable reflections, filter circuit selection, etc).

Second, many people are watching NTSC broadcasts of shows that were shot with high-def equipment. These always reach the limit of what NTSC can do.

Probably all TV production people have the pride that makes them want to put out the most attractive product possible. But some crews are prevented by their circumstances. For example, the equipment upkeep budget might be slashed because it is known that the equipment will soon be junked. Whatever the reason, it is always somehow economic.

I sometimes hear complaints that HD broadcasts aren’t quite as good as they could be. But this will always be true. At least now there is a higher target.

by Ken Nist