Better yet, about half of HD radio stations are taking advantage of multicasting: separate, different FM broadcasts  shadow channels  beamed out on the same frequency. They permit radio stations to experiment with niche, experimental and even interactive programming, usually commercial-free. WCBS-HD, an oldies station in New York, for example, has two shadow HD channels: one playing ’80s hits and one that’s a better-sounding version of the AM news channel.

And get this: all HD radio broadcasts are free. Take that, $13-a-month satellite!

O.K., so if HD radio offers so much and costs so little, how come nobody’s heard of it? How come fewer than a million people have tuned in?

One reason: confusion. It took years for the public to grasp satellite radio  and now we’re trying to sell people on yet another kind of radio?

(The name doesn’t help. According to hdradio.com, HD does not stand for high definition; “it is simply the branding language for this new technology.”)

Those cool shadow channels are confusing, too. You have to tune in the primary channel first. On some radio models, a “multicast” icon appears on the screen, if shadow channels are available. Then you hit the up/down tuning buttons to find the multicast channel. Try explaining that to Granddad.

HD radio also requires an HD radio receiver. Or, as HD radio’s tagline puts it, “If you don’t have an HD radio, you’re not hearing HD radio.” (Is that an advertisement  or a disclaimer?)

Image Among the receivers for HD radio is the Sony XDR-S10HDiP, which is also an iPod dock.

These radios aren’t especially expensive, but the setup can be intimidating to Mr. and Mrs. Average Person. Tabletop HD radios go for $75 and up. Thirteen car companies, mostly small ones, offer option packages that include HD radios. You can add an HD receiver to your existing car, too ($200 and up). There are no pocket HD radios.