What is HD Radio?

There's a new type of digital radio technology on its way -- and, unlike XM Radio and SIRIUS, it doesn't come via satellite. HD Radio is a new "high definition" format that brings you traditional terrestrial AM and FM stations with high-quality digital sound. With HD Radio, AM sounds almost as good as traditional FM, and FM has CD-quality sound. Let's take a further look.

How HD Radio Works

HD Radio is used by terrestrial AM and FM stations to broadcast their programming digitally. Traditional AM and FM broadcasts are relatively low-quality analog transmissions; by moving to digital, quality improves and additional features can be added.

The technology used by HD Radio is known as In-Band On-Channel (IBOC) broadcasting. It works by transmitting not one but three different signals for each radio channel -- a traditional analog signal, a digital signal, and a third signal that contains text data, such as song titles, traffic reports, stock data, and the like.

The three signals are bundled together into a single signal, which is then compressed using audio compression technology, so that it takes up less bandwidth. The combined signal is then transmitted from the radio station's digital transmitting antenna. When the signals reach your radio receiver, you hear either the analog feed (if you have a traditional AM/FM radio) or the digital feed (if you have a new HD Radio receiver). An HD Radio receiver also receives and decodes the accompanying text information, which is shown on the receiver's LCD display.

There are several benefits to broadcasting digital signals, chief of which is audio quality. A higher-quality signal can be sent in the same bandwidth used for the analog signal, which means that HD Radio sounds better than traditional AM or FM radio. In essence, AM now sounds like FM, and FM sounds like listening to a compact disc. It's that good. In addition, digital transmission eliminates multipath interference, which causes static in conventional radio receivers. Multipath interference is caused by the radio signal reflecting off building and other objects; a digital radio receiver recognizes the true signal from any reflections, and thus ignores interference. This reduces static, hiss, popping, and station fading. And the best thing about HD Radio is that it's free. Unlike satellite radio, you don't have to subscribe to HD Radio stations; they're the same AM and FM stations you listen to currently, but with much better sound quality.

HD Radio was developed by iBiquity Digital; you can learn more about HD Radio at the official HD Radio Website.

Michael Miller is a writer and commentator on technology and digital lifestyle topics.