Video waveform analysis made easy

As mentioned in the previous "Transition to Digital" newsletter, the broadcast television industry is experiencing another behind-the-scenes change bigger than the digital transition itself, which is the changing of the guard in engineering departments. Unlike on-camera stars, the best engineers tend to stay with the same station for decades. They learn the ropes, become a team leader and do their best to keep their station seamless until they retire or die. What some don’t do is to pass along valuable basic information the new engineers replacing them need to know.

Not all stations check the quality of video before or as it is ingested. Just because content comes in a file doesn’t necessarily mean it complies. Baseband video is even more suspicious. Most complies, but don’t assume all incoming content conforms to all audio and video specifications. To quote Ronald Reagan, “Trust but verify.” If you regularly verify, you may begin to develop a “usual suspects” list.

We’ve been discussing audio and the CALM Act lately, so we’ll pass on audio for now. Few tape decks or card docks contain video gain or chroma adjustments, so fixing a video problem without proc amp controls may need to be performed in an edit bay. It’s not efficient but if content isn’t manually verified and fixed before it airs, it can lead to greater problems later. Just because there are no knobs doesn’t mean it can’t be fixed.

Our analog world

Digital video has transformed the technology of television production, transmission and home viewing. However, digital video and audio begins and ends in analog, because light and sound are analog physical sensations. As such, they are captured by analog sensors such as microphones and CCDs, the latter after the analog light has already been processed by a lens and prism. At some point after that, the analog signal is converted to digital data. A digital data stream can be observed on a high-bandwidth oscilloscope, but it is rather impossible to make sense out of until it is converted to analog at the display or speaker.

You might think you could drive your car without gauges and a speedometer, and you probably could — until you are ticketed for speeding or the engine fails without warning. Your success is limited by the laws of physics and governing organizations, exactly as are baseband analog audio and video signals in a broadcast studio. Your dashboard in television production is a waveform monitor and vectorscope. They come in many form factors; stand-alone, rasterizers, built-in, and integrated in computer production and post-production programs. Here, we’ll simply refer to these devices as waveform monitors and vectorscopes. They might all work a little differently, but they all display the same analog information crucial for production, post and digital ingest. They’ve been ubiquitous since the early days of black and white television broadcasting, but the art of understanding them seems to be fading away. The purpose of this tutorial is to reintroduce operators to the basic operation of waveform monitors and vectorscopes.