HD Radio technology allows participating broadcasters to provide you with a higher fidelity digital AM and FM signal. Additionally, HD Radio stations often offer additional channels of content that is not available on the standard FM broadcast.

The digital signal is broadcast using a proprietary audio compression codec called HDC (High-Definition Coding). Current FCC rules also require stations to simulcast the same audio signal in analog as well, so if the primary digital signal is lost, the HD Radio receiver will revert to the analog signal, thereby proving seamless operation.

For HD AM broadcasts, the stations can choose broadcast rates between 40-60kbps, with most stations using the 40kbps as this method is more robust and less likely to cause dropouts due to signal strength issues. In theory the increased bandwidth on the AM band allows for AM radio at FM radio quality.

The FM HD broadcasts allow options to carry 100, 112, 125 or 150kbps of data when simulcasting with an analog signal. The system also has the capability of several pure digital modes up to 300kbps, however at the moment this would require a change to the current FCC ruling requiring the station to simulcast the signal in analog before stations can broadcast in pure digital.

FM stations also have the option to subdivide the digital audio streams into sub-channels (i.e. 87.5 HD1, HD2, etc.), which is often done to allow for more variety from one station. Each individual sub-channel can have its own audio quality from CD-quality (100kbps), FM-quality (25-50kbps), AM-quality (12kbps), or Talk-quality (5kbps).

For full information and to find stations in your area with HD please visit http://www.hdradio.com.