HD Radio™ technology is a digital radio standard developed by iBiquity Digital and recognized by the U.S. Federal Communications Commission (FCC). It works the same way that traditional analog transmits, except that the audio is digital formatted and transmitted as a continuous digital data stream in addition to the analog waveform signal.
On the broadcast end, audio is digitally compressed and broadcast by a transmitter designed specifically for HD Radio broadcasting. Audio is also transmitted in its analog form, as usual. The radio station sends out the analog and digital signals on the same broadcast frequency, along with the signals for the text data.
On the listener end, the signals are received and decoded. An HD Radio tuner picks up the digital radio transmission with its accompanying text. Older analog receivers continue to pick up the analog broadcasters.
Listeners can continue to enjoy their favorite stations on today’s analog receivers as well as on the new digital HD Radio receivers.
Currently, stations broadcasting in HD Radio are operating in a hybrid mode of both analog and digital in order reach both receivers. Eventually, as analog receivers are replaced by digital tuners, broadcasters may be able to turn off their analog signals and use that spectrum for more digital program channels or data applications.