Naming that tune -- or, better yet, remembering it -- could get easier for HD-radio listeners, thanks to tagging. 

Developed by Apple Inc. (APPL) and iBiquity Digital, which created the HD-radio-system technology, digital tagging lets listeners store the name of a song played on the radio so it can be played or bought at a later time through iTunes. 

“The concept of tagging allows people to not have to write down a song title whenever they hear a song,’’ said Chris Dragon, director of brand marketing at Harman International (HAR), owner of JBL, which is coming out with a portable HD radio that has built-in tagging. “They hear a song they like and they press a button.”

Unlike HD television, which is a must-have for many consumers because of the clearer picture, HD radio is just starting to take off. While it’s easy to see the benefit from having an HD television in your living room, HD radio is a harder sell. The industry has been promoting the clearer sound and greater content choices that come with HD radio but until now there weren’t many reasons to spend the extra money to buy an HD-radio receiver. The HD radio industry is betting tagging may change all that.

“Clear crisp sound was selling point 1.0,’’ said Robert Struble, chief executive of iBiquity. “Things like tagging are selling point 2.0. You begin to see that digital technology in radio is bringing more than just listening.”

In late March, Polk Audio, the unit of Directed Electronics (DEIX), was the first to come out with an HD radio that has iTunes tagging.

For $499, the portable HD radio and iPod docking station, called the I-sonic Entertainment System 2, lets users press a button when there’s a song that can be tagged. The song information, including title and artist will be stored in the iPod. Once you synch your iPod with iTunes, a playlist of tagged songs will appear in the iTunes store. You can then choose to purchase the song. The device can be found in Apple stores, at Polk Audio’s Web site, Amazon.com, Crutchfield.com and electronic retailers, including Best Buy (BBY), in the coming weeks.

“Tagging is one of the higher reasons people are buying our product,’’ said John Crisco, product line manager at Polk Audio. “People are excited about it. They get it and the demand has been good to date in the economic environment.”

According to Crisco, as more consumers learn about the concept of HD-radio tagging and as more vendors churn out products that incorporate tagging, the greater the adoption will be. “We need things to draw interest in technology,” said Crisco. “We have the first product to have this, but other products are coming through the summer. While we like being exclusive, having a larger push helps the entire group.”

JBL will launch its HD radio with iTunes tagging, called the JBL on Time 400IHD, in September. The device, which will sell for $299, is a combination iPod loudspeaker, dock, clock, am/fm radio and HD radio. The device will be about 14 inches wide and 4 inches in depth, small enough to fit on a nightstand.

“HD is a growing category,” said Dragon of JBL “The public at large is listening to more full-range music. This provides a way for consumers to embrace the new music. People won’t tag something they already know.”

But portable radios aren’t the only devices that have iTunes tagging. Car-radio maker Alpine Electronics has the TUA-T550HD HD radio tuner with tagging that works with its IDA-X100 and IVA-W505 car stereos.

The TUA-550HD is a small black box that connects to the Alpine stereo. With the add-on, drivers get HD-radio content in their cars. Both the iDA-X100 and the IVA-W505 stereo units have a button on the face of the radio for tagging a song. Users simply press the tag button when they hear a song they like and the information is transferred to the iPod. If the iPod isn’t connected to the tuner when a song is tagged, it will store up to 50 tags that are transferred when the iPod is connected. The HD radio tuner sells for $150.

While iTunes tagging is finally giving the HD-radio industry a “wow factor,” it’s not the only service iBiqutiy envisions for HD radio.  According to Struble, in the pipeline are things like instant and real time traffic and real-time information, including where the cheapest gas is or movie show times. The devices will even be able to store and play HD-radio content similar to what TiVo (TIVO) does for TV.

As for the devices that carry HD radio, Struble said portable radios, alarm clocks and car stereos are only the beginning.

“We’ve got a big effort to put the technology on to portable devices,” like MP3 players, cell phones, and personal-navigation devices, he said. “ITunes tagging begins to make the case that HD radio should be built into MP3 players.”