KAET-TV chief engineer Terry Harvey with the Linear Acoustic Model LA-5448 Multi-Input AC-3 Synchronizer and Rate Shaper (center).
KAET-TV, the PBS member station based at Arizona State University in Tempe, Ariz., is using a Model LA-5448 Multi-Input AC-3 Synchronizer and Rate Shaper supplied by Linear Acoustic last July to switch between incoming PBS multichannel audio soundtracks in AC-3 format and locally originated programming.
“We prefer to switch AC-3 bitstreams directly, simply because it avoids a series of decode and re-encode audio processing stages that can degrade audio performance,” says KAET-TV chief engineer Terry Harvey (pictured). And we can switch and splice compressed AC-3 audio streams without additional complicated routing systems.”
The LA-5448 also ensures that the essential metadata parameters encoded at PBS’ Washington headquarters, including DialNorm, are preserved and passed on to consumer receivers and set-top boxes.
“The LA-5448 has proved totally reliable in operation since we installed it last year,” Harvey adds. “It also saved us money on infrastructure costs, since we do not need complicated routing to handle AC-3-format data streams. And because the unit can handle a variety of data rates, we currently output our digital audio at a rate of 384 kbps. We could upsample to 448 kbps the feed from PBS, which currently runs at 384 kbps. When—and if—PBS increases its rate to 448 kbps, we are already fully compatible.
“In essence, the LA-5448 acts as an audio processing amplifier, much like the familiar Video Proc Amp,” Harvey concludes. “It cleans up our audio nicely, and ensures that when we switch the audio bitstream, which we do at least once a day to accommodate the PBS feeds, we produce clean AC-3 splices that are totally inaudible to our audience.”