Following four years of being on a pandemic-driven “hold,” the IEEE Broadcast Technology Society’s Fall Symposium resumed, with a return to its original Washington, D.C., home. The presentations took place at the new headquarters of the National Association of Broadcasters.
The November event attracted attendees from broadcast engineering, equipment manufacturing and academic sectors, and featured a variety of presentations on both technological advances and problems common to broadcasters.
Compression artifacts: are they something to worry about?
With compression technology now commonplace in transporting broadcaster’s FM multiplexes from studio to transmitter, Worldcast Systems’ Tony Peterle became curious about possible signal degradation, and this was the topic of his presentation.
Peterle said that while the focus of his testing was really on “what reaches a listener’s ears,” it included measurements of frequency response, distortion and stereo separation. He credited engineers Paul Shulins and Shane Toven for their assistance with the project.
The testing involved a representative sample of codecs, including units from 2WCom, APT, GatesAir, Omnia and Thimeo Audio Technology.
Peterle initially ran a “baseline” test without a codec, followed by runs with the various codecs and data rates. Speech, music and PPM information were all part of the testing.
Tests showed some amount of high-frequency roll-off, along with slightly increased distortion, with some variations observed among units under test. Stereo separation was generally acceptable.
Peterle did report inconsistencies, though, especially with PPM measurements, saying that in some cases, confidence scores were higher with compression than without.
“You can run the same signal through an encoder five times and you get five different results,” said Peterle. “There’s no consistency. More work needs to be done.” Radio World