HD Radio™ Glossary
Ralph Graves is one of Crutchfield's blog editors, and part of the company's social media team. He writes about home audio/video gear, specializing in Apple-related and wireless technologies. Ralph holds a master's degree in music composition, and his works have been released on various labels. He's served as product manager for an independent classical and world music label, produced several recordings, and worked extensively in public broadcasting. Since 1984 he's hosted a weekly classical music program on WTJU, and is also active as a blogger and podcaster.
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AM (Amplitude Modulation)
The primary method for radio broadcasting until the 1960s, when FM was introduced. An AM radio signal is broadcast at a constant frequency, with slightly varying strengths that alter the length of the carrier wave. Those changes in signal power, or modulation of amplitude, contain the station's audio signal. AM stations broadcast between 535 kilohertz (KHz) and 1700 KHz. AM signals are more susceptible to atmospheric interference than FM, and are of a lower fidelity.
The standard method for broadcasting in AM and FM. The carrier wave is modulated in a way that mirrors the source signals. As the music gets louder, for example, an AM wave increases in power, while an FM wave moves to a higher frequency. Atmospheric can interfere with analog signals, slightly altering the content. This results in a slight hiss often heard in the background, and — in the case of electrical storms — crackle and bursts of static. The physical environment can also cause interference, creating multipath distortion.
The range of frequencies that a station is assigned to broadcast in by the FCC. Bandwidth is measured in kilohertz in the AM range, and megahertz in the FM. It's also used to identify a station's position on the radio dial.
The radio wave that's modified to include a signal. In the case of AM transmission, the carrier wave's power is changed, or modulated. For FM broadcasts, the carrier wave's frequency is altered. Stations are assigned a bandwidth for their carrier waves.
Digital audio broadcasting
A radio wave comprised of digital information that is decoded by a compatible radio receiver into sound. Because the receivers read only the digital code, and ignore fluxuations in either the amplitude and frequency of the carrier wave, content is unaffected by atmospheric conditions, or subject to multipath distortion.
FM (Frequency Modulation)
A radio signal broadcast at a constant amplitude, with slight variations in frequency. These frequency differences carry the station's audio signal. FM stations broadcast between 88 megaherz (MHz) and 108 MHz. Because the strength (or amplitude) of the FM signal is constant, they are less susceptible to atmospheric interference than AM signals. It also allows the FM signal to carry more information. Most stations prefer to broadcast music in FM as it sounds fuller, and more readily allows for stereo separation.
iBiquity Digital Corporation's trademarked name for digital audio broadcasting. Although often misused, the term "HD Radio" is a trademarked brand name and does not stand for "High Definition Radio."
The term most commercial stations are using for the secondary digital audio broadcast channel. When the signal is divided for #multicasting the primary digital signal, sometimes known as HD1, duplicates the programming the station broadcasts as its main analog signal. The HD2 channel contains different programming not heard on the analog signal; it can only be received by HD Radios.
Short for the iBiquity Digital Corporation. iBiquity owns the technology that is now the United State's #iboc standard for digital audio broadcasts. It licenses the use of this technology, called HD Radio to broadcasters and electronic and radio equipment manufacturers.
IBOC (In Band On Channel)
The digital audio broadcasting standard adopted for the United States. Its name stems from the kind of signal being broadcast. IBOC signals use the same AM and FM bandwidth as a station's analog signal ("in band"). The digital information is contained within the station's signal, ("on channel").
A process that lets you select the song you're listening to for purchase at a later time. iTunes tagging requires a docking iPod; an audio/video component that includes an HD Radio tuner, iPod dock and "Tag" button; and a tagging-enabled HD Radio signal. When you hear a song you like, press the "Tag" button, and the component will store the song information (but not the song) in its memory. When you dock your iPod to the component, it will transfer all your saved tags to the iPod. The next time you sync your iPod to your computer, the tagged songs will appear as a list in iTunes. They then can be purchased through the iTunes store. You can also tag songs directly through the tuner in a 5th generation iPod nano®.
Subdividing the digital audio portion of a radio station's signal to send out different kinds of programming simultaneously. A multicasting station could, for example, broadcast Top 40 programming as their analog and primary digital format, while multicasting an additional digital-only channel for Oldies, and a third digital channel for News/Talk.
When parts of the same radio wave arrive at a receiver at different times. On its way from the transmitter to receiver, a radio wave can encounter obstacles such as tall buildings. These obstructions delay the arrival of part of the wave to the antenna. The result is slight distortion of the sound. This can be especially noticeable with stereo FM signals, where it may cause one channel to be slightly out of sync with the other.
RDS (Radio Data System)
The standard for sending digital text information along with an analog FM signal. The RDS feed usually contains information such as station IDs and slogans, which display on compatible radio receivers.
A process that lets you select the song you're listening to for purchase at a later time. Song tagging requires a Zune HD player and a tagging-enabled HD Radio signal. As you listen to an HD Radio station through the Zune, you can press a button and "tag" songs you like for later purchase. The Zune stores the song information (but not the song) in its memory. The next time you sync your Zune to your computer, the tagged songs will appear as a list in Zune Music Store. They then can be purchased through the store, and downloaded to your computer.