NBC and CBS engineering VPs outline the challenges of producing and transmitting in HD.
Audio problems, interoperability issues and compression artifacts have frustrated engineers facilitating the transition to HD production and transmission, according to two leading network TV engineers. Speaking yesterday at HD World, the executives offered advice based for their colleagues based on the experience they’ve gained producing some of the most watched sporting events on television.
The trickiest challenges have come from getting surround sound to transmit, intact, from t he studio to the TV set, said Dave Mazza, senior vice president of engineering, NBC Olympics. “As hard as everybody worked on HD video, where it hits the operators it’s relatively easy compared to surround sound,” he said. The biggest audio challenge Mazza and his crew encountered while producing the Winter Olympics in Turin, Italy, came at the editing console. Some NBC producers still prefer the speed of linear editing, so the company maintains both linear and non-linear editing seats, and the number of audio inputs can be a problem, particularly with the linear machines, Mazza said.
“We’re looking for a way to collect all the sound at six channels, edit it, delay it, then bring it back to six on the other side,” he said. “We’re looking for something that can make this six-to-two down-mix while allowing the sound to be editable and listenable.”
Lip sync poses another problem in HD, Mazza said, noting that many different pieces of equipment in the production chain automatically build in delays. Engineers must account for all these delays, or they’ll end up with audio that’s trailing slightly behind the video, he said.
Audio problems have also bedeviled the HD production and transmission effort at CBS, said Ken Aagaard, senior vice president of sports operations at the network. CBS began producing NFL games in HD five years ago, and when a complaint came in from a viewer, “invariably it was an audio issue,” he said.
Aagaard got so frustrated at one point that he began calling back the viewers who phoned during Sunday afternoon games to alert the network that they couldn’t hear parts of the broadcast. In once case, a viewer in Montana had to reprogram the audio menu on his new TV set, Aagaard said. In another, Aagaard had to work with his local cable company to fix a problem that was occurring only in some cable set-tops, including one of the ones in his own house.
After much trial and error, CBS learned that the key to flawless surround sound (or close to it), lies in the metadata that travels in signals along with the sound. “The metadata has to stay intact, from the mobile unit all the way to the viewer’s TV set,” Aagard said. This means it has to pass through encoders, editing equipment, compression equipment and other pieces in the chain without losing any pieces, he said. “If it gets interrupted, we’ll have problems.”
Mazza and Aagaard both indicated that the surround sound issues aren’t fully resolved, but their efforts appear to have tamed some of the worst offenses. “This year, for the first time, we’ve gotten some good reviews on the AVS Forum,” Aagaard said. Viewer complaints have also fallen way off. “In the past, we could get 100 complaints on a given Sunday,” he said. “Now, we get two or three.”
Interoperability issues have been less maddening, but they have slowed production efforts down, Mazza said. The most disheartening of these has been in the area of passing files from one camera format to another. “We had just gotten to the point where you could exchange files from one format to another in SD,” he said, but much of that progress dissolved when NBC switched to HD cameras. “We took three steps back on workflow relative to this issue,” he said. I’ve been making pleas to the manufacturers to create interoperable standards.”
Finally, compression can cause more artifacts in HD than in SD, if engineers aren’t vigilant, Mazza said. “With SD, you could squash the signal quite a long way and didn’t have as many concatenating compression artifacts that built up,” he said. “With HD, even if it looks good leaving the studio, that doesn’t mean it will look good when it leaves the station. The ATSC compressors turn the blurred effects that you didn’t notice into macro blocking.”