HD Radio

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HD radio
)

HD Radio logo.

HD Radio (HDR)

radio stations
in the United States, U.S. Virgin Islands, Canada, Mexico and the Philippines, with a few implementations outside North America.

The term "on channel" is a misnomer because the system actually broadcasts 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 two high-fidelity channels, while others use lower bit rates for voice-only news and sports. Previously these services required their own transmitters, often on low-fidelity AM. With HD, a single FM allocation can carry all of these channels, and even its lower-quality settings usually sound better than AM.

While it is typically used in conjunction with an existing channel it has been licensed for all-digital transmission as well. Four

FCC
in October 2020. 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.

History

U.S. Federal Communications Commission (FCC) in 2002 as a digital audio broadcasting method for the United States.[2][3] It is officially known as NRSC‑5, with the latest version being NRSC‑5‑D.[4]

DTS's eponymous theater surround sound systems.[5] The HD Radio technology and trademarks were subsequently acquired by Xperi Holding Corporation
in 2016.

HD Radio is one of several digital radio standards which are generally incompatible with each other:

  • FMeXtra was a competing U.S. standard, but has been stagnant since the 2010s.
  • Compatible AM Digital (CAM‑D) for AM stations.
  • a.k.a.
    Eureka 147, is the most common standard in Europe.
  • shortwave
    radio.

By May 2018, iBiquity Digital Co. claimed its HD Radio technology was used by more than 3,500 individual services, mostly in the United States.[6] This compares with more than 2,200 services operating with the DAB system.

A 400 

kHz. Thus most stations can transmit carefully designed digital signals on their adjacent channels without interfering with other local stations, and usually without co-channel interference with distant stations on those channels.[7]
Outside the U.S., the heavier spectral loading of the FM broadcast band makes IBoC systems like HD Radio less practical.

The FCC has not indicated any intent to end analog radio broadcasting as it did with analog television,[2] since it would not result in the recovery of any radio spectrum rights which could be sold. Thus, there is no deadline by which consumers must buy an HD receiver.

Technique

Digital information is

audio data compression algorithm.[9]

HD equipped stations pay a one-time licensing fee for converting their primary audio channel to iBiquity's HD Radio technology, and 3% of incremental net revenues for any additional digital subchannels.[10] The cost of converting a radio station can run between $100,000 and $200,000.[11] Receiver manufacturers who include HD Radio pay a royalty, which is the main reason it failed to be fully-adopted as a standard feature.[12]

If the HD receiver loses the primary digital signal (HD‑1), it reverts to the analog signal, thereby providing seamless operation between the newer and older transmission methods. The extra HD‑2 and HD‑3 streams do not have an analog simulcast; consequently, their sound will drop-out or "skip" when digital reception degrades (similar to digital television drop-outs). Alternatively the HD signal can revert to a more robust 20 

kbit/s stream, although the sound quality is then reduced to conventional AM-level. Datacasting is also possible, with metadata
providing song titles or artist information.

iBiquity Digital claims that the system approaches CD quality audio and offers reduction of both interference and static.[13] 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. (see § AM, below).

AM

An example of information displayed by an AM HD station locking.

The AM hybrid mode ("MA1") uses 30 

kHz), and overlaps adjacent channels on both sides of the station's assigned channel.[4] Some nighttime listeners have expressed concern this design harms reception of adjacent channels[14][15] with one formal complaint filed regarding the matter: WYSL owner Bob Savage against WBZ
in Boston.

The capacity of a 30 

kbit/s
mode, which features redundancy (same data is broadcast twice).

The digital radio signal received on a conventional

forest canopy
, or similar.

All-digital AM

All-digital AM ("MA3") allows for two modes: "Enhanced" and "core-only".[17]

Beyond the station's 0.5 
kHz
of bandwidth.
  • In core-only mode, the station only transmits the primary carriers.

When the receiver can only decode the primary carriers in either mode, the audio will be mono and only text information can be displayed. The narrower bandwidth needed in either all-digital mode compared to hybrid mode reduces possible interference to and from stations broadcasting on adjacent channels.[18] However, all-digital AM lacks the analog signal for fallback when the signal is too weak for the receiver to decode the primary digital carrier.

Four stations have operated as all-digital / digital-only broadcasters:

  • FCC since July 2018 to broadcast all-digital.[19]
  • WMGG (since January 2021), WFAS (since May 2021) and WSRO (since December 2021) broadcast all-digital under new rules adopted by the FCC on 27 October 2020 that allow any AM station to voluntarily choose to convert to all-digital operation.[20] However, WMGG subsequently dropped MA3 and WSRO left the air.[21]

FCC concluded from WWFD
's experiments:

"The [experimental] record does not establish that an audio stream on an [AM] HD-2 subchannel is currently technically feasible".[23]

The FCC requires stations that wish to multiplex their digital AM signals to request and receive permission to do so;[23] in early 2020 it rejected a multiplex request from WTLC.[24]

FM

HD Radio DX during a band opening
HD Radio transmitter
Spectrum of FM broadcast station without HD Radio
Spectrum of FM broadcast station with HD Radio
HD Radio Emergency Alert System test using KDKA-FM HD‑1

The

kbit/s
signal.

FM stations can divide their datastream into sub-channels (e.g., 88.1 HD‑1, HD‑2, HD‑3) of varying audio quality. The multiple services are similar to the

kbit/s
.

FCC rules require that one channel be a simulcast of the analog signal so that when the primary digital stream cannot be decoded, a receiver can fall back to the analog signal. This requires

station ID
.

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. This is because all analog receivers process analog signals faster than digital radios can process digital signals. The digital processing of analog signals in an HD Radio also delays them. 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. It is more noticeable with simple voice transmission than with complex musical program content.[b]

Stations can transmit HD through their existing antennas using a

destructive interference
at any given location where they may be received.

Artist Experience

HD Radio supports a service called "Artist Experience"[26] in which the transmission of album art, logos, and other graphics can be displayed on the receiver. Album art and logos are displayed at the station's discretion, and require extra equipment. An HD Radio manufacturer should pass the iBiquity certification, which includes displaying the artwork properly.

EAS alerts

Since 2016, newer HD Radios support

AMBER
, and security alerts can be displayed on the radio. As with "Artist Experience", emergency alerts are displayed at the station's discretion, and require extra equipment.

HD Radio bandwidth
Spectrum of a HD Radio station as shown by a RTL-SDR USB device. The usual bandwidth of a regular FM station is visible as the marker width in the top image.

Bandwidth and power

transmitter/studio link for in-house telemetry
.

In (regular) hybrid mode a station has ±130 

kHz) that must be shut down to use extended hybrid can be restored through use of digital subchannels
. However, this requires the replacement of all related equipment both for the broadcasters and all of the receivers that use the services shifted to HD subchannels.

The ratio of power of the analog signal to the digital signal was initially standardized at 100:1 (−20 dBc), i.e., the digital signal power is 1% of the analog carrier power. 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. Unlike with subcarriers, where the total

broadcast translators
, which are secondary and therefore left unprotected from such interference. Other broadcasters are also opposed (or indifferent), since increasing power would require expensive changes in equipment for many, and the already-expensive system has so far given them no benefit.

There are still some concerns that HD FM will increase interference between different stations, even though HD Radio at the 10% power level fits within the FCC spectral mask.

kHz apart. An HD broadcast station will not generally cause interference to any analog station within its 1 mV/m service contour – the limit above which the FCC protects most stations. However, the IBOC signal resides within the analog signal of the immediately adjacent station(s). 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.[32][33][34]

On 29 January 2010, the U.S. FCC approved a

broadcast class
, these numbers are relative to that lower limit rather than their actual power.

Comparison to other digital radio standards

HD versus DAB

Some countries have implemented

kbit/s
in digital-only mode.

The first generation

AAC
standard.

Before DAB+ was introduced, DAB's inefficient compression led in some cases to "downgrading" stations from

Mbit/s bandwidth.[38]

Digital radio, such as DAB, DAB+, and HD FM often have smaller coverage of markets as compared to analog FM, radios are more expensive, and reception inside vehicles and buildings may be poor, depending on the frequencies used. HD Radio shares most of these same flaws (see criticisms below). On the other hand, digital radio allows for more stations and less susceptibility for disturbances in the signal. In the United States, however, other than HD Radio, digital broadcast technologies, such as DAB+, have not been approved for use on either the VHF band II (FM) or medium wave band.

DAB is well suited to national broadcasting networks that provide several stations as is common in Europe, whereas HD is more appropriate for individual stations.

HD versus DRM

DRM+
, and HD AM and HD FM.

Similar to HD AM, DRM allows either hybrid digital-analog broadcasts or pure digital broadcasts, DRM allows broadcasters to use multiple options:

  • Hybrid mode (digital/analog) - 10 kHz analog plus 5 kHz digital bandwidth allows 5–16 
    kbit/s
    data rate;
  • 10 kHz digital-only bandwidth confined to ±5 kHz of the channel center allows 12–35 kbit/s;
  • 20 kHz digital-only bandwidth using ±10 kHz (including half of the adjacent channels) allows 24–72 kbit/s.

On the medium wave, actual DRM bit rates vary depending on day versus night transmission (

groundwave versus skywave
) and the amount of bits dedicated for error correction (signal robustness).

Although DRM offers a growth path for AM broadcasters, unfortunately it shares many of the same flaws as DAB and HD AM:

  • Shorter broadcast distance in hybrid mode compared to an analog AM signal
  • Poor reception inside vehicles and buildings
  • Interference with adjacent channels when using the 20 
    channel mask
    .

VHF bands (1, 2, and 3),[39] either as a hybrid analog-digital or digital only broadcast, but with 0.1 MHz digital-only bandwidth, it allows 186.3 kbit/s data rate[40][41]
(compared to HD FM with 0.4 MHz allowing 300 kbps.)

Digital Radio Mondiale is an

licensing. HD Radio is based upon the intellectual property of iBiquity Digital Co. / Xperi Holding Co.
The United States uses DRM for
shortwave broadcasts.[42]

Acceptance and criticism

Awareness and coverage

According to a survey dated 8 August 2007 by Bridge Ratings, when asked the question, "Would you buy an HD Radio in the next two months?" Only 1.0% responded "yes".[43]

Some

broadcast engineers have expressed concern over the new HD system.[44] A survey conducted in September 2008 saw a small percentage of participants that confused HD Radio with satellite radio.[45]

Many first-generation HD Radios had insensitive receivers, which caused issues with sound quality. The HD Radio digital signal level is 10–20 dB below the analog signal power of the station's transmitter. In addition, commentators have noted that the analog section of some receivers were inferior compared to older, analog-only models.[46]

However, since 2012, HD capable receiver adoption has significantly increased in most newer cars, and several aftermarket radio systems both for vehicles and home use contain HD Radio receivers and special features such as Full Artist Experience. iBiquity reports that 78% of all radio listening is done on stations that broadcast in HD.[47] There are an increasing number of stations switching to HD or adding subchannels compatible with digital radio, such as St. 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.[48]

Different format and compatibility standards

Even though DAB and DRM standards are open standards and predate HD Radio, HD receivers cannot be used to receive these stations when sold or moved overseas (with certain exceptions; there are HD stations in Sri Lanka,[49][needs update] Thailand, Taiwan, Japan, Romania, and a few other countries).

DAB and DRM receivers cannot receive HD signals in the U.S. The HD system, which enables AM and FM stations to upgrade to digital without changing frequencies, is a different digital broadcasting standard. The lack of a common standard means that HD receivers cannot receive DAB or DRM broadcasts from other countries, and vice versa, and that manufacturers must develop separate products for different countries, which typically are not dual-format.

Whereas the Advanced Audio Coding (AAC) family of codecs are publicly documented standards, the HDC codec exists only within the HD system, and is an iBiquity trade secret.

Similarly DAB or DRM are open specifications, while iBiquity's HD specification is partly open, but mostly private.[clarification needed][50]

HD Radio does not use

MHz
frequency, eliminating the former dual-medium compatibility of channel 6 television stations.

Reduced-quality concerns

Promotion for HD Radio often fails to make clear that some of its features are mutually incompatible with other features. For example, the HD system has been described as "CD quality"; however, the HD system also allows multiplexing the data stream between two or more separate programs. A program utilizing one half or less of the data stream does not attain the higher audio quality of a single program allowed the full data stream. The FCC has declared

"one
over-the-air digital stream [must be] of equal or greater quality than the station's existing analog signal".[51]

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

NDS
claims that RadioGuard will "provide additional revenue-generating possibilities".

Mostly all existing FM receivers tuned to a channel broadcasting a HD signal are prone to increased noise on the analog signal, called "HD Radio self-noise", due to analog demodulation of the digital signal(s). In some high fidelity FM receivers in quality playback systems, this noise can be audible and irritating. Most all existing FM receivers will require modifications to the internal filters or the addition of a post-detection filter to prevent degradation of the analog signal quality on stations broadcasting HD Radio.

Reduced analog signal

Radio stations are licensed in the United States to broadcast at a specific

RF interference on FM. However the boosted digital HD signal coverage would then exceed analog coverage, with 17% more population covered in vehicles but 17% less indoors.[53]

High costs

The costs of installing the system, including fees, vary from station to station, according to the station's size and existing infrastructure. Typical costs are at least several tens of thousands of dollars at the outset

LPFM stations. During mid-2010 a new generation of HD Radio broadcasting equipment was introduced, greatly lowering the startup costs[f]
of implementing the system.

HD Radio receivers cost anywhere from around

dollar stores
. Although costs have historically been higher for HD hardware, as adoption has increased, prices have been reduced, and receivers containing HD Radio are becoming more commonplace – especially as more stations broadcast in HD format.[citation needed]

Power consumption

Conventional analog-only FM transmitters normally operate with "class C" amplifiers, which are efficient, but not linear; HD Radio requires a different amplifier class. A class C amplifier can operate with overall transmitter efficiency higher than 70%.[g] Digital transmitters operate in one of the other amplifier classes – one that is close to linear, and linearity lowers the efficiency. A modern hybrid HD FM transmitter typically achieves 50~60% efficiency, whereas an HD digital-only FM transmitter should manage just 40~45%. The reduced efficiency causes significantly increased costs for electricity and for cooling.

Programming

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.). Now, iBiquity works with the major owners of the stations to provide various additional choices for listeners, instead of having several stations independently deciding to create the same format. HD‑1 stations broadcast the same format as the regular FM (and some AM) stations, and many of these stations offer one, two, or even three subchannels (designated HD‑2, HD‑3, HD‑4) to complement their main programming.

KFRG-FM and KSCF‑FM
into Los Angeles) via HD‑2 and HD‑3 channels.

On 8 March 2009, CBS Radio inaugurated the first station with an HD4 subchannel, WJFK-FM in Washington, D.C., a sports radio station which also carries sister sports operations WJZ-FM from Baltimore; Philadelphia's WTEL‑AM and WIP-FM; and WFAN‑AM from New York.[i][54] Since then numerous other channels have implemented HD‑4 subchannels as well, although with nearly 100% talk-based formats, because of the reduced audio quality. For example, KKLQ‑FM in Los Angeles operates an HD‑4 signal and aired The Mormon Channel which was 99% talk.[55]

KCMP-FM, on 89.3 FM in the Twin Cities, offers "Wonderground Radio", music for kids and their parents, on 89.3 FM‑HD2.[56]

KCMP-FM on 89.3 FM‑HD2 in Los Angeles.[57]

Univision Radio for their former frequency. The programming on the WNYC-FM‑HD2 channel now is a rebroadcast of WQXR-FM, in order to give full coverage of WQXR-FM programming in some form, as the 105.9 FM
signal is weaker, and does not cover the whole area.

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. This restored WITI‑TV's audio to the Milwaukee radio dial after a two-month break, following the digital transition; as a channel 6 analog television station WITI‑TV exploited the 87.7 FM audio quirk as an advantage, in order to allow viewers to hear the station's newscasts and Fox programming on their car radios.

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. Branded as "The Crossing", it is operated by Azusa Pacific University
.

College radio has also been impacted by HD Radio, stations such as WBJB-FM which is a public station on a college campus offer a student run station as one of the multicast channels. WKNC-FM in Raleigh, NC, runs college radio programming on HD‑1 and HD‑2, and electronic dance music on WolfBytes Radio on WKNC-FM‑HD3.

Some commercial broadcasters also use their HD‑2 channels to broadcast the programming of noncommercial broadcasters.

WMXD-FM's HD‑2 channel. On a similar note, Los Angeles' KRRL 92.3 FM‑HD3 signal rebroadcasts EMF's Air1, and in Santa Barbara KLSB 97.5 FM airs K-Love on its primary frequency, and rebroadcasts Air1 on HD‑2 (though neither supports "Artist Experience"). In St. Louis, Missouri, WFUN 96.3-HD2 rebroadcasts K297BI
for the classical music station Classic 107.3.

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.[59]

Translators

Although

LPFMs
might have been licensed otherwise.

In addition to the controversial practice of converting the HD-only secondary radio channels of a primary station into analog FM in areas where the primary station's signal can already readily be received, translators can also be used in a more traditional manner to extend the range of the full content of the primary station, including the unmodified main signal and any HD Radio sub-channels, in areas where the station has poor coverage or reception, as is done via the remote transmitter K202BD in Manti, Utah, which rebroadcasts both the analog and digital signals of KUER-FM from Salt Lake City.

In order to do this, HD Radio may be passed along from the main station via a "

radio antenna if either is too narrowband to pass the wider HD Radio signal, meaning one or both might have to be replaced. Baseband translators which use a separate receiver and transmitter require an HD Radio transmitter, just as does the main station. Translators are not required to transmit an HD Radio digital signal, and the vast majority of existing translators which repeat FM stations
running hybrid HD signals do not repeat the HD part of the radio broadcast, due to technical limitations in equipment designed before the advent of HD Radio technology.

Receivers

Automotive and home/professional

HD‑1 signal on KOST 103.5 FM in a Volkswagen RCD‑510 receiver

By 2012, there were several HD receivers available on the market. A basic model costs around US$50.

Automotive HD receiver manufacturers include:

Most car manufacturers offer HD receivers as audio packages in new cars, including:

Home and office listening equipment is available from a number of companies in both component receiver and tabletop models, including:

Portable

Sangean HDR‑14 portable receiver playing San Diego's KPBS-FM HD‑2 channel, "Classical 24".

Initially, portable HD receivers were not available due to the early chipsets either being too large for a small enclosure and / or needing too much power to be practical for a battery-operated device. 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. Two companies made low-power chipsets for HD receivers:

At least five companies made portable HD receivers:

By 2012, iBiquity was trying to get HDR chipsets into mobile phones.

Footnotes

  1. ^ Station identification is sent by voice, or as RBDS data, but not all stations transmit RBDS.
  2. ^ Note that the "reverb" effect is limited to analog vs. digital receivers, or in rare cases, digital receivers with remarkably different circuitry. Multiple receivers that are all HD (of the same make and model, at least), or multiple receivers that are all analog, in the same room or house, will not produce a noticeable echo.
  3. ^ Holm (2007)[37] The sound quality in DAB digital radio, SUMMARY (in English):
    This analysis of the audio quality of DAB has been made independently of the broadcasting companies and aims at balancing their information. Through measurement of the audio signal and through informal listening, we have found that DAB suffers from several problems:
    • The stereo image is smeared due to heavy use of joint stereo coding. Often the stereo image lacks focus and gives incorrect localization of instruments, in certain cases there is also incorrect balance between a vocalist and the background music.
    • The treble cut-off frequency is usually as low as 14 kHz and the result is a lack of brightness and a veiled sound stage. In particular young people will notice this degradation.
    As young people are the target group for some of these stations, such as P3, this must be considered to be very undesirable. The reason is that the bit rates for all the channels in the Norwegian DAB network today are much lower than what scientific evaluation of audio quality has recommended, i.e. lower than 192–256 kbit/s which was projected when DAB was debated in Stortinget (Norwegian Parliament) in 1998. When the capacity is fully utilized, stations with music in the Oslo area use these bit rates:
    • Three stations use 160 kbit/s with an audio quality similar to FM: P2, Alltid Klassisk1 and P4
    • Twelve stations use 128 kbit/s with lower quality than FM, incl. P1 and P3.
    • Two stations transmit in mono at rates of 80 and 96 kbit/s (Radio 2 Digital Moox and NRK Barn2)
    It would have been desirable to stop using 128 kbit/s as the standard bit rate for music, and use 160 bit/s instead. More demanding material should have the same quality as MP3 at 128 kbit/s, i.e. 192 kbit/s in DAB. As of today, there is not capacity to increase bit rates to these levels, so the DAB network has too low capacity with respect to requirements for decent audio quality.
    The broadcast companies want us to make a choice between FM, with the best audio quality in stationary receivers, and DAB which is best in a car. Today this is an unnecessary choice as there are no technological problems in making a digital radio which is better than FM on all accounts:
    • Reception without garbling in cars
    • Capacity for all the stations one wants
    • Audio with near-CD quality
    — Steve Holm (2007)[37]
  4. ^ Former U.S. analog TV channel 6 occupied the upper end of the lower
    MHz
    .
  5. ^
    NDS Group is a maker of digital media encryption
    technology.
  6. ^ a b HF Radio startup costs include transmitter, diplexer (or a new, separate
    feedline
    ), and installation labor.
  7. ^ "
    electrical power it consumes. Efficiencies differ by amplifier class, ranging over all classes from 25% at the worst-of-the-worst, to 90% at the best-of-the-best
    .
  8. ^ The
    Clear Channel Communications
    ).
  9. ^ Note however, that at some point, the
    Dallas, Texas, sister sports station KRLD-FM
    .
  10. ^ Hirschmann Car Communication GmbH is now a subsidiary of TE Connectivity.
  11. ^ SiPort is a Santa Clara, CA, startup acquired by Intel in 2011.[63]

References

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  4. ^ a b "NRSC‑5‑D standard" (PDF). nrscstandards.org. National Radio Systems Committee. Retrieved 14 April 2021.
  5. DTS
    . 2 September 2015.
  6. ^ "HD Radio broadcasters". HD Radio (hdradio.com). iBiquity Digital Corporation.
  7. ITU
    ‑R BS.412.
  8. ^ "Receiving NRSC‑5". theori.io. 9 June 2017. Archived from the original on 20 August 2017. Retrieved 14 April 2018.
  9. ISBN 978-1-136-03410-7
    .
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  11. Consumer Electronics Association. Archived from the original
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  12. ^ "Becoming an HD Radio IP licensee". ibiquity.com. iBiquity Digital Corporation. Archived from the original on 31 December 2008. Retrieved 31 December 2008.
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  14. ^ Zuk, Karl (20 November 2007) [Sep 2007]. "Night of the bees". Write or Karl me! (karlzuk.blogspot.com). Archived from the original on 8 July 2011. Retrieved 31 December 2008.
  15. ^ MP3 sample of the interference: IBOC observations. WYSL 1040 AM (wysl1040.com) (mp3 soundclip). Archived from the original on 25 March 2009.
  16. ^ "SBR explained". Dolby. Coding Technologies. Archived from the original on 16 December 2008. Retrieved 31 December 2008.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  17. ^ "Commission unanimously approves all-digital AM radio broadcasting". wiley.law. 30 October 2020. Retrieved 29 May 2021.
  18. ^ In the matter of all-digital AM broadcasting revitalization of the AM radio service – comments of Hubbard Radio, LLC (PDF) (Report). Hubbard Radio, LLC. 9 March 2020. MB Docket No. 19-311, MB Docket No. 13-249. Retrieved 15 April 2021 – via Federal Communications Commission.
  19. ^ "WWFD 820 AM becomes first all-digital AM station". Radio-Online. 16 July 2018.
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  21. ^ "Crawford Will Flip an Alabama AM to All-Digital". Radio World. 22 August 2023. Retrieved 22 August 2023.
  22. ^ Fybush, Scott (6 December 2019). "HD‑2 arrives on AM radio". fybush.com. NERW extra. Retrieved 15 April 2021.
  23. ^ a b All-digital AM broadcasting – revitalization of the AM radio service (PDF) (Report). FCC fact sheet. U.S. Federal Communications Commission. 6 October 2020. FCC-CIRC2010-05 / doc 367361A1.
  24. ^ "FCC to vote on authorizing all-digital AM". radioinsight.com. FCC Report. 11 October 2020.
  25. ^ "Stations in Maryland broadcasting on HD Signals". iBiquity Digital Corporation. Archived from the original on 13 July 2011. Retrieved 3 July 2016.
  26. ^ Juan@HDRadio [user name] (24 July 2013). "Artist Experience". HD Digital Radio (hdradio.com). Archived from the original on 25 July 2016. Retrieved 14 April 2018. {{cite web}}: |author= has generic name (help)
  27. ^ Juan@HDRadio [user name] (28 October 2016). "Sparc HD Radio receiver w/Bluetooth and emergency alerts". HD Digital Radio (hdradio.com). Get a radio / home radio. Archived from the original on 14 April 2018. Retrieved 14 April 2018. {{cite web}}: |author= has generic name (help)
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  29. ^ "NRSC-5-D In-band/on-channel Digital Radio Broadcasting Standard" (PDF). nrscstandards.org. Consumer Technology Association & National Association of Broadcasters. April 2017. p. 10. Retrieved 15 February 2022.
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  31. ^ "iBiquity spurious noise and emissions mask TX SSS 1026s rev E and FCC Part 73.317 FM emission broadcast limits". Radio World (radioworld.com). Guest commentaries. New Bay Media, LLC. Figure 1 1014. Archived from the original on 28 June 2017. Retrieved 7 November 2009.
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External links

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