The German automaker was one of the first to offer HD Radio as an option, beginning in 2006, and has offered the feature as an option across all model lines since 2007. BMW has enabled HD Radio's built-in data capabilities for real-time traffic information features in its vehicles.
HD Radio has been slow to take off (the format was approved by the FCC back in 2002), but transmissions are now available to about 85 percent of Americans, with about 2,000 stations broadcasting in the format.
HD uses a digital signal and, like digital broadcast TV, it allows additional channels though so-called multiplexing or multicasting. Typically, with no complications, HD2 and HD3 streams can carry data (such as traffic or weather information) or additional audio channels.
TheCarConnection.com has tested a number of vehicles with HD Radio and finds that the sound quality isn't quite as warm and clear as a nearby FM broadcast—though loud music sounds better in HD than with satellite services like Sirius and XM. The real improvement comes in AM-band HD Radio transmissions, where sound quality doesn't vary as much and volume doesn't rise and fall as with an analog signal.
With a number of cars soon becoming capable of streaming audio directly to the instrument panel—including the upcoming MyFord Touch and MyLincoln Touch systems, which will offer Pandora and Stitcher apps—the days for subscription services like satellite radio might be numbered. However HD Radio remains free once you have the tuner.
A number of automakers have recently announced plans to expand HD Radio capability in their vehicles. In January, Audi said that it will make HD available on many 2011 models, while Volkswagen hinted that it will bring HD Radio to its better-equipped models in the form of a touch-screen system.