The radio industry’s answer to the Internet, iPods and satellite radio has been slow to make waves with consumers.

Called HD Radio, the technology allo ws radio stations to transmit a digital signal in addition to a traditional analog signal. Plus, extra stations, called “HD-2” or “HD-3,” allow broadcasters to offer a wider range of programming in a static-free medium. And listeners don’t have to pay subscription fees charged for satellite radio.

But four years after the first HD radios hit the marketplace, the new service hasn’t gained traction with consumers. For one thing, the signal can be heard only through special digital radio receivers, with prices that start at about $80. And just some of the nation’s radio stations offer extra HD-2 or HD-3 channels — with programming that often isn’t much different from what broadcasters play on their primary frequencies. Moreover, the digital signal typically doesn’t reach as far as the same station’s analog signal, so in many cities, the signal comes and goes as listeners drive around town.

These drawbacks are temporary, argues Bob Struble, chief executive of Ibiquity Digital Corp., the company that licenses and develops HD Radio technology. He points to improvements, such as steadily lowering prices for HD radios, along with some innovative HD stations.

Still, some industry veterans say HD Radio’s rollout was bungled and fear that the window of opportunity is rapidly closing as other audio entertainment options, like Apple Inc.’s iPod music players, become entrenched. “If they don’t get HD Radio going right now, they’re going to lose it,” says Bill Figenshu, a Skytop, Pa., consultant to radio and other media companies.

But Struble says those aren’t the right comparisons. Because HD radio represents an upgrade rather than a brand new technology, it makes more sense to compare it to the rollout of FM in an AM-dominated radio environment or to color television in a world of black and white. Both technologies took years to become dominant. “If folks expect this to be a one- to two-year transition, that’s not realistic,” he says.

HD Radio is trying to find ways to piggyback on other popular products, like creating HD tuners with docking stations for iPods and a feature that allows users to tag songs for purchase later on iTunes.

Despite millions of dollars spent developing and marketing HD radio, consumers’ awareness and enthusiasm for the new technology is hard to gauge. The industry-backed HD Radio Alliance, citing a survey it commissioned from Critical Mass Media, says three out of four radio listeners know about the technology. But an independent study from ratings service Arbitron Inc. and Edison Media Research released earlier this year says only about one in four had heard or read “anything recently about HD Radio.” Since that study, the industry has launched an aggressive advertising campaign for HD Radio.

Of some 13,000 radio stations in the country, about 1,800 are broadcasting digitally. About 84 percent of Americans live in an area where they can hear at least one HD radio station, Ibiquity says.

Work is also needed on the retail side, where some consumers report walking into big electronics stores, asking for HD radio receivers and being led instead to the section for satellite radio.

About 100 different models will be available in stores this holiday season, up from just 30 last year, according to Ibiquity. Yet persuading holiday shoppers of HD Radio’s merits poses another challenge. The lure of extra HD stations isn’t always all it’s cracked up to be, with too many sounding just like what is already on the dial — a classic-rock station might offer deep-cuts classic rock on its HD-2 channel, for example. With such routine fare, “the audience is going to give you a big ho-hum,” says Figenshu.

There is a silver lining for HD-2 stations, however. Most are also running on the Internet, where the better ones seem to be making headway. In Detroit, the much-praised WRIF’s Riff 2 plays a mixture of rap and rock, genres that are normally strictly segregated on regular radio. It got about 6,000 streams in September, meaning 6,000 visits by people who turned on the online feed. In Denver, rock outlet 97.3 KBCO’s HD 2 station, Studio C, got about 13,000 streams in September with its playlist of music sets collected from 20 years of musician visits to its station.

For the technology to really catch on with offline listeners, radio veterans say, the industry needs to beef up the number of HD-2 and HD-3 stations and increase the strength of the signal.

Already, the industry has filed a report with the Federal Communications Commission, advocating the signal upgrade. Some broadcasters object, saying stronger digital signals from nearby stations might cut into their own signals. National Public Radio, a big HD player, supports the upgrade, but with some protection measures in the roughly 15 percent of cases where it estimates serious interference might result. Those measures could include limiting the signal increase to core urban areas, says Mike Starling, NPR’s chief technology officer.

The industry also needs to make sure HD radios are widely available in cars. But now that the price of the chipsets is dropping, making the extra cost of HD Radio just $30 to $50 for car makers, the technology is creeping into more auto showrooms. Next year, for example, HD Radio will be standard in new Volvos.Local stations that broadcast in HD

 WPRO-HD…92.3 FM 

 WSNE-HD…93.3 FM 

 WSNE-HD2…93.3-2 FM 

 WHJY-HD…94.1 FM 

 WWBB-DH…101.5 FM 

 WWBB-HD2…101.5-2 FM 

 WWLI-HD…105.1 FM 

 WWKX-HD…106.3 FM 

 WDDZ-HD…550 AM 

 WPRO-HD…630 AM 

 WHJJ-HD…920 AM 

 WRNI-HD…1290 AM