Most of the HD stations I listened to for this article broadcast two separate channels, playing different content.
Al Fasoldt's reviews and commentaries, continuously available online since 1983

T e c h n o f i l e
HD radio is here, and you don't have to pay much to enjoy it

March 16, 2008

By Al Fasoldt
Copyright © 2008, Al Fasoldt
Copyright © 2008, The Post-Standard

   Radio is changing. You'll have more stations to choose from, better signals and, in some cases, more "hi" in your "fi."
   You can give all the credit to HD radio, a new way of broadcasting FM and AM programs. Nationwide, there are 1,600 HD stations already in operation, with 92 here in New York State. Central New York has about a half-dozen HD stations.
   The Federal Communications Commission (FCC) approved a national rollout of HD radio in March 2007. But many U.S. stations put off converting until recently. Stations don't have to convert -- there's no FCC requirement that radio be HD like there is for television, which has to be all digital a year from now -- but most stations are converting anyway.
   HD Radio is not "high definition" radio. You're excused if you're confused over this. After all, "HD" means "high definition" when it comes to television, so why not for radio, too?
   But in radio broadcasting "HD" stands for "hybrid digital," referring to the way HD radio stations can let their regular analog signals go along for the ride when they broadcast in digital sound. Non-HD radio receivers simply ignore the digital component, but HD radios pick up the digital versions. (They'll also play all the analog stations in your area, too.)
   Unlike satellite radio, which requires a subscription fee, HD radio is free. But both methods are alike in one way: They both use so-called perceptual encoding when they compress the audio signal. This should seem familiar to iPod users because it uses a variation of the encoding method that squeezes music down to smaller file sizes that will fit onto a portable player. (Yes, that means, more or less, that you're listening to MP3s all the time on HD radio.)
   Most of the HD stations I listened to for this article broadcast two separate channels, playing different content. Broadcasters love this feature, which gives them the potential of selling advertising for twice as much program time. But listeners should benefit, too, especially if broadcasters devote more time to the kind of alternative programs that are usually aired only on on Sunday mornings when almost no one is listening.
   The HD radio I borrowed is the HD100 from Radiosophy, which lists for $100. You can buy it direct from www.radiosophy.com or from discount outlets such as Amazon.com. The HD100 looks a little old-fashioned -- I think the '50s look adds to the friendliness -- and is about the size of a tall loaf of bread. Controls work normally, without any need to learn something new in the digital radio age. One feature I liked is an option to lock out all non-digital stations when it scans for signals. You can still tune the old-fashioned stations manually, but auto-scanning will only pick up HD broadcasts.
   Like a car radio, the HD100 has easy-to-program preset buttons for your favorite stations, and, like your old clock radio, it will wake you up to music in the morning. (And, yes, if you're like me, you'll appreciate the fact that there's a snooze button, too.)
   The radio's display screen shows the station and, if necessary, the sub-channel you're tuned to, along with the time. (Oddly, you have to set the time yourself. If my computer can keep the right time automatically, HD radios should, too. This facility seems to be missing in the HD radio specifications.)
   Sound quality was uninspiring through the small built-in speakers, but college students living in dorms should note that the audio quality through the front headphone jack was much better. The radio even has a pair of auxiliary input jacks on the back so you can hook up your MP3 player or iPod and get room-filling sound.
   I wasn't able to test HD quality on AM stations -- there just weren't any HD AM broadcasts when I was listening -- but others who use HD radios for AM listening have given mixed reviews. I'd stick to FM for HD anyway.