HD Radio

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HD Radio (HDR) is a trademark for in-band on-channel (IBOC) digital radio broadcast technology. HD radio generally simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD Radio is used primarily by FM radio stations in the United States, U.S. Virgin Islands, Canada, Mexico and the Philippines, with a few implementations outside North America. HD Radio transmits the digital signals in unused portions of the same band as the analog AM and FM signals. As a result, radios are more easily designed to pick up both signals, which is why the HD in HD Radio is sometimes referred to stand for Hybrid Digital, not "High Definition". Officially, HD is not intended to stand for any term in HD Radio, it is simply part of iBiquity's trademark, and does not have any meaning on its own. HD Radios tune into the station's analog signal first and then look for a digital signal. The European DRM system shares channels similar to HD Radio, but the European DAB system uses different frequencies for its digital transmission. The term "on channel" is a misnomer because the system actually sends the digital components on the ordinarily unused channels adjacent to an existing radio station's allocation. This leaves the original analog signal intact, allowing enabled receivers to switch between digital and analog as required. In most FM implementations, from 96 to 128 kbit/s of capacity is available. High-fidelity audio requires only 48 kbit/s so there is ample capacity for additional channels, which HD Radio refers to as "multicasting". HD Radio is licensed so that the simulcast of the main channel is royalty-free. The company makes its money on fees on additional multicast channels. Stations can choose the quality of these additional channels; music stations generally add one or...