HD Radio allows conventional (or terrestrial) AM and FM stations to broadcast their content over digital signals. Appropriating an abbreviation from high-definition TV, HD Radio offers better sound quality than AM and FM radio bands. It also allows stations to add more programming via several additional channels that can be broadcast "alongside" a station's main frequency. Stations often use these subchannels to provide traffic or weather information, or diverse music content.
And just as with AM and FM, once you have a compatible radio, there is no subscription fee for the service. There are more than, 2,000 HD Radio stations across the U.S., according to iBiquity Digital, the company that developed the technology. Still, HD Radio is only in its infancy.
Unlike digital TV, HD Radio broadcasts won't replace analog broadcasts (at least not in the near future) but will run parallel to them.
Stations supporting HD Radio simultaneously broadcast analog and digital versions of the same programming over the same frequency. With a regular radio, you'll hear the usual analog version. With a HD-compatible radio, the radio tunes in to the digital programming on HD stations and the analog signals for non-HD stations.
If a HD Radio signal becomes too weak, the radio will automatically switch over to the parallel analog signal.
Here's more on how HD Radio differs from regular analog radio:
It offers better sound quality
In our tests, HD Radio can live up to its promise of improved sound. The HD Radio sound quality delivers deeper bass, higher treble, more stereo separation, and a greater dynamic range (the difference between the loudest and quietest sounds) than FM or AM signals.
At its best, HD Radio pushes FM sound quality closer to that of CDs and makes AM broadcasts resemble those of analog FM.
Moreover, the HD signal from AM stations is in stereo, and there is no background noise—the hiss or crackle you occasionally hear with standard radio.
Programming is more varied
Many of the stations that have converted to HD radio in the United States have added a second (and some even a third) subchannel with different programming than the stations' main frequency.
You tune in the subchannels with a tap of a toggle or a turn of the tuning knob; they appear in the display with a designation such as FM2.
A station can have up to eight subchannels and they typically carry programming of a different music genre than the main channel. The primary station might be adult contemporary, for example, while a subchannel might offer gospel or country to broaden the station's appeal.
(For a full list of HD Radio stations and their formats, visit www.hdradio.com.)
Still, don't expect anywhere near the variety you get with satellite radio. HD Radio stations often carry no commercials on subchannels, but the main channels carry the usual commercials.
You get more information
As with satellite radio, HD Radio stations can show you the song title, artist, and other data on a display. Some stations also use the display to provide local traffic, weather, stock prices, news alerts, and more.
In the future, using technology to identify specific receivers, a vehicle could receive designated signals, whether additional audio channels (concerts or extra sports channels, for example) or specialized services, like "closed-caption" text for the hearing impaired. Such services would be broadcast by a station along with its main channels.
Tag and buy
Some HD stations enable "tagging," which lets you flag a song for later purchase through iTunes. This requires an iPod with a dock and a radio with tagging capability.
Expect some service interruptions
In our testing around the New York area, we had little trouble tuning in many New York-area HD Radio stations. With some, however, we received the analog signal but not the digital one. When the digital signal for the main (HD1) service wasn't strong enough, the radio switched to the analog broadcast.
When the digital signals faltered for an HD2 subchannel, however, programming simply stopped, resulting in a pattern of interruptions.
HD-compatible aftermarket radios and converters for the car are on sale from number of major manufacturers, typically with prices of about $100 and up.
Your choices include in-dash HD Radio compatible head units; tuners that connect to radios designated HD Radio Ready; tuners that connect to factory-installed audio systems behind the dash; and transportable units that can be used both in the car and at home.
Most automakers offer HD Radio in premium audio systems.
Earlier table models for home use from Boston Acoustics, Cambridge Soundworks, Jensen, Sangean, and Sony have been pricey, at $200 and up. But prices have been dropping and table top units start around $100. Portable units begin at about $50.