[opendtv] HD radio experience

In a different thread, I reported my first impressions of the Sangean HDT-1 stereo AM/FM IBOC tuner. The setup was simple, just like any AM/FM tuner. I use the same antenna(s) for FM as I use for TV, and for AM they give you a loop antenna. Or you can set up your own longwire antenna for AM.
As I reported last night, FM and digital FM sound very good. When the unit first tunes in a station, if an analog signal is available, it immediately tunes to that. Then in a couple of seconds, it switches to the digital signal. Sound quality is very good either way. The demodulated digital signal is slightly louder than the analog, in this Sangean tuner, so that might lead people to assume the digital is better. I have to do more listening to say for sure. I'd say the digital has some of that typical digital edge, much like you hear in digital movie soundtracks. That is usually attributed to sharp cutoff low-pass filters. In any case, in the FM band, the sound is very nice and you get more programs as a bonus. Low subwoofer bass is excellent as well. And the FM analog tuner is excellent in this unit as well, as I mentioned yesterday.
Since I installed the tuner in the evening, the AM band had no digital programming. Testing out the AM band's digital had to wait for today. Well, in the AM band, the difference is nothing short of dramatic. There are a few local AM stations here that transmit IBOC, and in each case, the "AM sounds like FM" slogan you hear is about right. One caveat is that the only programming I could test this on is talk, but certainly the muddy sounding AM voice was gone, replaced by crystal clear voice, with sibillants clearly audible, just like good FM. (Then again, if you modulated AM in a 30 KHz band, that would sound pretty good too!)
The fact that digital, over the FM band, is 23 dB weaker than the analog signal is certainly a reason why it doesn't seem to travel all that far. Another possible reason is that IBOC does the equivalent of assigning low-power digital stations exclusively adjacent to high power analog stations, just the sort of situation ATSC receivers have trouble with. Whatever the case may be, the result is that ATSC is considerably more successful than IBOC for long range signals, during this analog-to-digital transitional phase.
I'm actually impressed by the Ibiquity proprietary codec. Whatever they did, not bad at all considering that the FM IBOC signal is only 98 Kb/s total when analog is present! 

Bert

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