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General Radio Discussion / Re: HD FM Audio Drives Me Nuts
« on: December 11, 2019, 0507 UTC »The HD and analog paths are processed very differently. Any lossy codec as a rule does not like clipped audio, as it contains more harmonic energy that it must process, with varying success. Instead, look-ahead limiting is used, but as a consequence, produces some intermodulation distortion. The analog path is processed conventionally. The codec for HD also makes use of spectral band replication, which can cause all sorts of wierd artifacts on its own. It all depends on what data rate the station has set their importer/exporter up for, and this is largely determined by how many HD sub channels they have.
There is a long standing theory that American DAB (HD) has a self-noising property. Some more detail can be found here http://ham-radio.com/k6sti/hdrsn.htm
Also within the last few years, the Arbitron PPM system has been toyed with by several manufacturers in an attempt to boost the host stations' ratings. They do this by making the PPM signal louder, and in many cases unmasking the tones. It seems to be most noticeable on dry voice, and makes the announcer sound as if they are in a broom closet, or talking through a paper towel tube. The device responsible for this is made by Telos, called the voltair. https://www.telosalliance.com/25-Seven/Voltair
It's a race to the bottom. The voltairs running on large corporate stations here have made the stations unlistenable for me. My favorite station here switched on HD about 18 months ago, and I immediately noticed their audio quality drop. Everything got sort of fuzzy sounding.
+-RH
But do stations use Voltairs on their HD channels?