HD Radio
The system sees little use elsewhere due to its reliance on the sparse allocation of FM broadcast channels in North America; in Europe, stations are more tightly spaced.
iBiquity developed HD Radio, and the system was selected by the U.S. Federal Communications Commission (FCC) in 2002 as a digital audio broadcasting method for the United States.
A 400 kHz wide channel is required for HD FM analog-digital hybrid transmission, making its adoption problematic outside of North America.
Furthermore, long-standing FCC licensing practice, dating from when receivers had poor adjacent-channel selectivity, assigns stations in geographically overlapping or adjacent coverage areas to channels separated by (at least) 400 kHz.
[9] Outside the U.S., the heavier spectral loading of the FM broadcast band makes IBoC systems like HD Radio less practical.
[13] Receiver manufacturers who include HD Radio pay a royalty, which is the main reason it failed to be fully-adopted as a standard feature.
[15] However, the data rates in HD Radio are substantially lower than from a CD, and the digital signals sometimes interfere with adjacent analog AM band stations.
[16] Some nighttime listeners have expressed concern this design harms reception of adjacent channels[17][18] with one formal complaint filed regarding the matter: WYSL owner Bob Savage against WBZ in Boston.
HD FM also provides several pure digital modes with up to 300 kbit/s rate, and enabling extra features like surround sound.
Although the signals may be synchronized at the transmitter and reach the receiving equipment simultaneously, what the listener hears through an HD unit and an analog radio played together can be distinctly unsynchronized.
The resulting unmistakable "reverb" or echo effect from playing digital and analog radios in the same room or house, tuned to the same station, can be annoying.
The limitation assures that the two transmissions have nearly the same broadcast range, and that they maintain the proper ratio of signal strength to each other so as not to cause destructive interference at any given location where they may be received.
HD Radio supports a service called "Artist Experience"[29] in which the transmission of album art, logos, and other graphics can be displayed on the receiver.
This low power, plus the uniform, noise-like nature of the digital modulation, is what reduces its potential for co-channel interference with distant analog stations.
With the proposed power increase of 10 dB, the potential exists to cause the degradation of the second-adjacent analog signals within its 1 mV/m contour.
Before DAB+ was introduced, DAB's inefficient compression led in some cases to "downgrading" stations from stereophonic to monaural, in order to include more channels in the limited 1 Mbit/s bandwidth.
Cloud, Minnesota, where many local radio outlets find a growing number of listeners tuning in to their HD signals, which in turn has benefited sales.
The FCC has declared If the FCC disallows analog simulcasting, each station will have over 300 kbit/s bandwidth available, allowing for good stereo quality or even surround sound audio, together with multiple sub-channels, and to a lesser extent more freedom for low-power, personal FM transmitters, to pair modern smartphones, computers, and other devices to legacy analog FM receivers.
The broadcasting industry is seeking FCC approval on future HD receiver models, for conditional access; that is, enabling the extra subchannels to be available only by paid subscription.
NDS[e] has made a deal with iBiquity to provide HD Radio with an encrypted content-delivery system called "RadioGuard".
During mid-2010 a new generation of HD Radio broadcasting equipment was introduced, greatly lowering the startup costs[f] of implementing the system.
Until 2013, the HD Digital Radio Alliance,[h] acted as a liaison for stations to choose unduplicated formats for the extra channels (HD‑2, HD‑3, etc.).
It is common practice to broadcast an older, discontinued format on HD‑2 channels; for example, with the recent disappearance of the smooth jazz format from the analog radio dial in many markets, stations such as WDZH‑FM in Detroit, Michigan, (formerly WVMV), WFAN-FM in New York City, and WNWV-FM in Cleveland, Ohio, program smooth jazz on their HD‑2 or HD‑3 bands.
CBS Radio is implementing plans to introduce its more popular superstations into distant markets (KROQ-FM into New York City, WFAN‑AM into Florida, and KFRG-FM and KSCF‑FM into Los Angeles) via HD‑2 and HD‑3 channels.
WMIL-FM in Milwaukee has offered an audio simulcast of Fox affiliate WITI‑TV on their HD‑3 subchannel since August 2009 as part of a news and weather content agreement between iHeartRadio and WITI‑TV.
KYXY‑FM, operated by CBS in San Diego on 96.5 FM and offers their HD‑2 channel as one of the few "subchannel only" independent Christian music based formats on HD Radio.
Also, in Detroit, WMXD-FM, an urban adult contemporary station, airs the contemporary Christian K-Love format on its HD‑2 band (the HD‑2 also feeds several analog translators around the metropolitan area – see below), due to an agreement between iHeartMedia and K-Love owner Educational Media Foundation (EMF), allowing EMF to program WMXD-FM's HD‑2 channel.
In July 2018, as part of a projected one year experiment, WWFD‑AM in Frederick, Maryland, became the first AM station to eliminate its analog transmissions and broadcast exclusively in digital.
In order to do this, HD Radio may be passed along from the main station via a "bent pipe" setup, where the translator simply makes a frequency shift of the entire channel, often by simple heterodyning.
However, in January 2008 at the Consumer Electronics Show (CES) in Las Vegas, iBiquity unveiled a prototype of a new portable receiver, roughly the size of a cigarette pack.
