Apple, iBiquity Digital Corp, a developer of high-definition radio technology, and major radio companies said on Friday they are offering a new, free service called "iTunes Tagging."

The service lets listeners with HD Radio receivers containing a special tag button, to "tag" songs they hear on the FM dial for subsequent purchase via Apple's iTunes.

"iTunes tagging takes music discovery on the radio to the next level," said Greg Joswiak, Apple's vice president of iPod Product Marketing, in a statement.

iBiquity said various broadcasters, including radio market leader Clear Channel Communications Inc , came together quickly for the initial launch across hundreds of stations.

The tagging button will be available on HD radios made by Harman International Industries Inc's JBL unit and Polk Audio, recently purchased by Directed Electronics Inc. .

U.S. radio operators are working to promote HD Radio, which receives over-the-air terrestrial stations with CD-quality sound and multiple new-program formats, in an effort to better compete with ever increasing digital music options. The industry has pledged to spend $250 million on marketing through the HD Digital Radio Alliance.