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HD Radio logo.
List of digital radio broadcast standards
DAB standards
5G Broadcast
ISDB standards
AM band in-band on-channel (AM IBOC)
FM band in-band on-channel (FM IBOC)

HD Radio (HDR)[1] 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,[citation needed] 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".[2] 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.[3] 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.[4]

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 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 AM stations use the all-digital format, one under an experimental authorization, the other three under new rules adopted by the 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

[edit]

This standard was meant to supersede other existing stereophonic standards on AM.

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.[5][6] It is officially known as NRSC‑5, with the latest version being NRSC‑5‑E.[7]

iBiquity was acquired by DTS in September 2015 bringing the HD Radio technology under the same banner as DTS's eponymous theater surround sound systems.[8] 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:

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.[9] This compares with more than 2,200 services operating with the DAB system.

A 400 kHz wide channel is required for HD FM analog-digital hybrid transmission, making its adoption problematic outside of North America. In the United States, FM channels are spaced 200 kHz apart as opposed to 100 kHz elsewhere. 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. 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.[10] 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,[5] 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

[edit]

Digital information is transmitted using OFDM with an audio compression format called HDC (High-Definition Coding). HDC is a proprietary codec based upon, but incompatible with, the MPEG-4 standard HE-AAC.[11] It uses a modified discrete cosine transform (MDCT) audio data compression algorithm.[12]

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.[13] The cost of converting a radio station can run between $100,000 and $200,000.[14] Receiver manufacturers who include HD Radio pay a royalty,[15] which is the main reason it failed to be fully-adopted as a standard feature.

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.[16] 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

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

The AM hybrid mode ("MA1") uses 30 kHz of bandwidth (±15 kHz), and overlaps adjacent channels on both sides of the station's assigned channel.[17] Some nighttime listeners have expressed concern this design harms reception of adjacent channels[18][19] with one formal complaint filed regarding the matter: WYSL owner Bob Savage against WBZ in Boston.[citation needed]

The capacity of a 30 kHz channel on the AM band is limited. By using spectral band replication the HDC+SBR codec is able to simulate the recreation of sounds up to 15,000 Hz, thus achieving moderate quality on the bandwidth-tight AM band.[20] The HD Radio AM hybrid mode offers two options which can carry approximately 40~60 kbit/s of data, with most AM digital stations defaulting to the more-robust 40 kbit/s mode, which features redundancy (same data is broadcast twice).

The digital radio signal received on a conventional AM receiver tuned to an adjacent channel sounds like white noise – the sound of a "hiss", or a large waterfall, or a strong, steady wind through a dense forest canopy, or similar.

All-digital AM

[edit]

All-digital AM ("MA3") allows for two modes: "Enhanced" and "core-only".[21]

  • In enhanced mode, the primary, secondary and tertiary carriers are transmitted, allowing for a maximum throughput of 40.2 kbit/s while using 20 kHz of bandwidth out to the station's 0.5 mV/m contour. Inside this contour, stereo audio along with graphics (station logo and "artist experience" album artwork) and text information (the station's call sign, title, album, and artist) can be decoded by the receiver.
Beyond the station's 0.5 mV/m contour, typically only the primary carriers can be received, which restricts the maximum throughput to 20.2 kbit/s while only requiring 10 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.[22] 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.

Five AM stations have operated as all-digital / digital-only broadcasters, either on an experimental basis or 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.[23]

  • WWFD (WSHE since June 2024) was granted special temporary authority from the FCC in July 2018 to broadcast all-digital.[24] It continues broadcast in digital-only mode under regular authorization.
  • WMGG broadcast in all-digital mode from January 2021 until a new owner returned it to analog-only mode following a station sale in November 2021.
  • WFAS broadcast in digital-only mode from May 2021 until its license was deleted in October 2024.
  • WSRO broadcast in digital only-mode from December 2021 until the station went silent in March 2023. After a brief return to the air in 2024, its license was cancelled in March 2025.
  • WYDE broadcast in all-digital mode from September 2023 until June 2025 when it returned to broadcasting in hybrid mode.[25][26]

The FCC requires stations that wish to multiplex their digital AM signals to request and receive permission to do so.[27] WWFD experimented with using a digital subchannel, operating a second channel (HD2) at a low data rate while reducing the data rate of the primary channel (HD1).[28] In October 2020, the 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".[27] In early 2020 the FCC rejected a multiplex request from WTLC.[29]

FM

[edit]
HD Radio DX during a tropo 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 FM hybrid digital / analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of data carrying (lossy) compressed digital audio depending upon the station manager's power budget and desired range of signal. HD FM also provides several pure digital modes with up to 300 kbit/s rate, and enabling extra features like surround sound. Like AM, purely-digital FM provides a "fallback" condition where it reverts to a more robust 25 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 digital subchannels found in ATSC-compliant digital television using multiplexed broadcasting. For example, some top 40 stations have added hot AC and classic rock to their digital subchannels, to provide more variety to listeners.[30] Stations may eventually go all-digital, thus allowing as many as three full-power channels and four low-power channels (seven total). Alternatively, they could broadcast one single channel at 300 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 synchronization of the two, with a significant delay added to the analog service. In some cases, particularly during tropospheric ducting events, an HD receiver will lock on to the digital stream of a distant station even though there is a much stronger local analog-only station on the same frequency. With no automatic identification of the station on the analog signal, there is no way for the receiver to recognize that there is no correlation between the two.[a] The listener can possibly turn HD reception off (to listen to the local station, or avoid random flipping between the two stations), or listen to the distant stations and try to get a 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 diplexer, as on AM, or are permitted by the FCC to use a separate antenna at the same general location, or at a site licensed as an analog auxiliary, provided it is within a certain distance and height referenced to the main analog signal. 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.

Artist Experience

[edit]

HD Radio supports a service called "Artist Experience"[31] 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

[edit]

Since 2016, newer HD Radios support Bluetooth and Emergency Alert System (EAS) alerts[32] in which the transmission of traffic, weather alerts, 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

[edit]

FM stereo stations typically require up to 280 kilohertz of spectrum. The bandwidth of an FM signal is found by doubling the sum of the peak deviation (usually 75 kHz) and the highest baseband modulating frequency (around 60 kHz when RBDS is used). Only 15 kHz of the baseband bandwidth is used by analog monaural audio (baseband), with the remainder used for stereo, RBDS, paging, radio reading service, rental to other customers, or as a transmitter/studio link for in-house telemetry.

In (regular) hybrid mode a station has ±130 kHz of analog bandwidth. The primary main digital sidebands extend ±70 kHz on either side of the analog signal, thus taking a full 400 kHz of spectrum. In extended hybrid mode, the analog signal is restricted to ±100 kHz. Extended primary sidebands are added to the main primary sidebands using the extra ±30 kHz of spectrum created by restricting the analog signal.[33] Extended hybrid provides up to approximately 50 kbit/s additional capacity.[34] Any existing subcarrier services (usually at 92 kHz and 67 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 baseband modulation is reduced, there is no reduction to the analog carrier power. The National Association of Broadcasters (NAB) requested a 10 dB (10×) increase[35] in the digital signal from the FCC. This equates to an increase to 10% of the analog carrier power, but no decrease in the analog signal. This was shown to reduce analog coverage because of interference, but results in a dramatic improvement in digital coverage. Other levels were also tested, including a 6 dB or fourfold increase to 4% (−14 dBc or 25:1). National Public Radio was opposed to any increase because it is likely to increase interference to their member stations, particularly to their 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.[36] North American FM channels are spaced 200 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.[37][38][39]

On 29 January 2010, the U.S. FCC approved a report and order to voluntarily increase the maximum digital effective radiated power (ERP) to 4% of analog ERP (−14 dBc), up from the previous maximum of 1% (−20 dBc).[40] Individual stations may apply for up to 10% (−10 dBc) if they can prove it will not cause harmful interference to any other station. If at least six verified complaints of ongoing RF interference to another station come from locations within the other station's licensed service geographic region, the interfering station will be required to reduce to the next level down of 4%, 2% (−17 dB), or 1%, until the FCC finally determines that the interference has been satisfactorily reduced.[41] The station to which the interference is caused bears the burden of proof and its associated expenses, rather than the station that causes the problem. For grandfathered FM stations, which are allowed to remain over the limit for their broadcast class, these numbers are relative to that lower limit rather than their actual power.

Asymmetric sidebands

[edit]

In May 2025 the FCC confirmed it would permit asymmetric sideband levels to be used[42]. The total power in the asymmetric side bands must not exceed that which would be permitted when the sidebands are symmetrical. The use of asymmetrical sidebands can reduce interference to an adjacent FM channel.

Comparison to other digital radio standards

[edit]

HD versus DAB

[edit]

Some countries have implemented Eureka-147 Digital Audio Broadcasting (DAB) or the newer DAB+ version. DAB broadcasts a single multiplex that is approximately 1.5 megahertz wide (≈1 megabit per second). That multiplex is then subdivided into multiple digital streams of between 9~12 programs (or stations). In contrast, HD FM requires 400 kHz bandwidth – compatible with the 200 kHz channel spacing traditionally used in the ITU Region 2 (including the United States) – with capability of 300 kbit/s in digital-only mode.

The gradually phased out first generation DAB uses the MPEG-1 Audio Layer II (MP2) audio codec which has less efficient compression than newer codecs. The typical bitrate for DAB stereo programs is 128 kilobit per second or less and as a result most radio stations on DAB have a poorer sound quality than FM does under similar conditions.[43] Many DAB stations also broadcast in mono. In contrast, DAB+ uses the newer AAC+ codec and HD FM uses a codec based upon the MPEG-4 HE-AAC standard.

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.[44]

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 better suits national broadcasting networks that provide several stations as is common in Europe, whereas HD is more appropriate for individual stations.

HD versus DRM

[edit]

Digital Radio Mondiale (DRM 30) is a system designed primarily for shortwave, medium wave, and longwave broadcasting with compatible radios already available for sale. DRM 30 is similar to HD AM, in that each station is broadcast via channels spaced 10 kHz (or 9 kHz in some regions) on frequencies up to 30 MHz. The two standards also share the same basic modulation scheme (COFDM), and HD AM uses a proprietary codec. DRM 30 operates with xHE-AAC, historically with any of a number of codecs, including AAC, Opus, and HVXC. The receiver synchronization and data coding are quite different between HD AM and DRM 30. As of 2015 there are several radio chipsets available which can decode AM, FM, DAB, DRM 30 and 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, it shares some issues with HD Radio in the AM:

  • Shorter broadcast distance in hybrid mode compared to an analog AM signal
  • Interference with adjacent channels when using the 20 kHz mode though in all-digital mode the signal fits inside the designated channel mask.

DRM+, a different system based upon the same principles of HD Radio on the FM band, but can be implemented in all the VHF bands (1, 2, and 3),[45] 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[46][47] (compared to HD FM with 0.4 MHz allowing 300 kbps.)

Digital Radio Mondiale is an open standards system, albeit one that is subject to patents and licensing. HD Radio is based upon the intellectual property of iBiquity Digital Co. / Xperi Holding Co. The United States uses DRM for HF / shortwave broadcasts.[48]

Acceptance and criticism

[edit]

Awareness and coverage

[edit]

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".[49]

Some broadcast engineers have expressed concern over the new HD system.[50] A survey conducted in September 2008 saw a small percentage of participants that confused HD Radio with satellite radio.[51]

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.[52]

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.[53] 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.[54]

Different format and compatibility standards

[edit]

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,[55][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.[56]

HD Radio does not use ATSC, the standard for digital television in the United States, and so fails to recover the former TV and FM radio compatibility enjoyed by TV channel 6 broadcasters. In the days of analog television, the lowest sliver of the FM broadcast band (87.7–87.9 MHz) overlapped with the FM audio carrier of U.S. analog television's channel 6;[d] because the NTSC analog television standard used conventional analog FM to modulate the audio carrier, the audio of television stations that broadcast on channel 6 could be heard on most FM receivers. In earlier days of television and radio, several television stations exploited this overlap and operated as radio stations. Full-powered television stations were forced to cease their analog broadcasts in June 2009, and low-powered stations ceased analog broadcasts by July 2021. Because the digital television and all digital radio standards are incompatible, HD receivers are not able to receive digital TV signals on the 87.75 MHz frequency, eliminating the former dual-medium compatibility of channel 6 television stations. Current low-power ATSC 3.0 channel 6 stations that broadcast an audio carrier on 87.75 do not have HD Radio.

Reduced-quality concerns

[edit]

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 free over-the-air digital stream [must be] of equal or greater quality than the station's existing analog signal".[57]

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".[58] 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

[edit]

Radio stations are licensed in the United States to broadcast at a specific effective radiated power level. In 2008, NPR Labs did a study of predicted HD Radio operation if the digital power levels were increased to 10% of the maximum analog carrier power as is now allowed by the FCC under certain circumstances, and found the digital signal would increase 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.[59]

High costs

[edit]

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[f] plus per-channel annual fees (3% of the station's annual revenue[citation needed]) to be paid to Xperi for HD‑2 and HD‑3 (HD‑1 has no royalty charge). Large companies in larger media markets – such as iHeartRadio or Cumulus Broadcasting – can afford to implement the technology for their stations. However, community radio stations, both commercial and noncommercial, in many cases cannot afford the US$1,000 yearly Xperi fee assessed to 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 US$50 to several hundred dollars, compared to regular FM radios which can sometimes even be found at 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

[edit]

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

[edit]

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.

iHeartRadio is selling programming of several different music genres to other competing stations, in addition to airing them on its own stations. Some stations are simulcasting their local AM or lower-power FM broadcasts on sister stations' HD‑2 or HD‑3 channels, such as KFNZ-FM in Kansas City simulcasting 610 AM KFNZ's programming on 96.5 FM‑HD2. 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. Some HD‑2 or HD‑3 stations are even simulcasting sister AM stations. In St. Louis, for example, clear-channel KMOX‑AM (1120 kHz analog and HD) is simulcast on KEZK-FM 102.5 FM‑HD3. KBCO‑FM in Boulder, Colorado, uses its HD‑2 channel to broadcast exclusive live recordings from their private recording studio. 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.

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][60] 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.[61]

Public broadcasters are also embracing HD Radio. Minnesota Public Radio offers a few services: KNOW-FM, the MPR News station in the Twin Cities, offers music service Radio Heartland on 91.1 FM‑HD2 and additional news programming called "BBC News and More" on 91.1 FM‑HD3; KSJN-FM, the classical MPR station in the Twin Cities, provides "Classical 24" service on 99.5 FM‑HD2; and KCMP-FM, on 89.3 FM in the Twin Cities, offers "Wonderground Radio", music for kids and their parents, on 89.3 FM‑HD2.[62]

KPCC‑FM (Southern California Public Radio), heard on 89.3 FM in Los Angeles, offers a digital simulcast of its analog channel on 89.3 FM‑HD1 and MPR's music service KCMP-FM on 89.3 FM‑HD2 in Los Angeles.[63]

New York Public Radio in New York City, WNYC (AM) and WNYC-FM, (d.b.a. WNYC) re-broadcasts a locally programmed, all-classical service from WQXR-FM called "Q2", on 93.9 FM‑HD2. The service launched in March 2006.[64] On 8 October 2009, the format was moved to WQXR‑HD2 (WXNY-FM) on 105.9 FM when WQXR-FM was acquired by New York Public Radio as part of a frequency swap with 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.

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. 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. Bonneville International uses its HD‑2 and HD‑3 channels to broadcast Mormon Channel which is entirely noncommercial and operates solely as a public service from Bonneville's owner, The Church of Jesus Christ of Latter-day Saints. That network of eight HD‑2 and HD‑3 stations was launched on 18 May 2009 and was fully functional within two weeks. 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. 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.[65]

Translators

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Although FM broadcast translators are prohibited from originating their own programming, the FCC allows translator stations to rebroadcast an HD Radio subchannel of the primary station it is assigned to, instead of the programming of that station's analog signal. Station owners in large markets have taken advantage of this rule to allow HD subchannels to be heard on analog FM, or take AM licenses with attached translators silent while continuing to feed the translator.

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. Translators are not required to transmit an HD Radio signal, and the vast majority of existing translators do not.

Receivers

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Automotive and home/professional

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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

[edit]
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:

  • Coby Electronics Corporation produced the first HD portable – the Coby HDR‑700 portable HD receiver for both AM and FM.[70]
  • Griffin Technology produced an HD receiver designed to plug into the dock connector of an Apple iPod, or iPhone, with tuning functionality provided via software through the device's multi-touch display. This product was discontinued.
  • Best Buy started selling the Insignia NS‑HD01, a house brand portable unit on 12 July 2009. It was the second portable HD receiver to come to the general market and featured FM‑only playback and a non-removable rechargeable battery which charges via mini USB. The Insignia unit sold in 2009 for around US$50 – the least expensive receiver available.[71] Best Buy discontinued the NS‑HD01 model by September 2019 in favor of the NS-HD02.
  • Microsoft released the Zune HD on 15 September 2009. It included an HD receiver embedded in the media device.[72] The Zune HD was discontinued in November 2011 in favor of Windows Phones.
  • Sangean Electronics produces multiple portable HD radios with AM and FM reception, like the Sangean HDR-14 portable receiver.

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

Footnotes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

HD Radio

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from Grokipedia
HD Radio is a proprietary digital radio broadcasting technology that enables AM and FM radio stations to transmit high-quality digital audio signals, along with ancillary data services, within the same frequency band as their existing analog broadcasts using an in-band on-channel (IBOC) method. Developed by iBiquity Digital Corporation (now part of Xperi Corporation), it operates in a hybrid mode where digital sidebands flank the analog signal, allowing receivers to blend between the two for optimal reception, or in an all-digital mode for AM stations to eliminate analog interference and expand coverage. The technology adheres to the NRSC-5-E standard set by the National Radio Systems Committee, supporting bit rates up to 96 kbit/s for FM hybrid audio and providing CD-quality sound without requiring spectrum reallocation. Key features of HD Radio include multicasting, which permits stations to broadcast up to seven supplemental program services (HD2 through HD8) in addition to the primary program service (), for a total of eight channels simultaneously on a single frequency, expanding content options like additional music formats or talk programming. It also delivers advanced data services, including song titles, artist information, album art, traffic updates, and weather alerts displayed on compatible receivers, enhancing the listener experience without subscription fees. The system uses perceptual audio coding for compression and includes error correction for robust signal performance, particularly in urban environments where multipath interference is common. Since its approval by the (FCC) on October 11, 2002, as the standard for terrestrial in the United States, HD Radio has seen gradual adoption, with over 2,500 stations transmitting more than 4,500 digital channels as of 2025. Primarily integrated into automotive receivers—available in vehicles from 25 major brands—it has become the dominant format in , though listener penetration remains limited to about 80% of listening occurring on HD-capable stations as of September 2025 due to the need for specialized hardware. The FCC authorized all-digital in 2020 to address noise and interference issues, further supporting the technology's evolution toward full digital transition.

History

Development and Early Adoption

The development of HD Radio began in the 1990s when major U.S. broadcasters CBS, Gannett, and Westinghouse formed the USA Digital Radio consortium in 1991 to create an in-band on-channel (IBOC) digital transmission system that would allow digital signals to coexist with existing analog broadcasts without requiring additional spectrum. This effort led to foundational patents for IBOC technology, including U.S. Patent No. 5,315,583 (filed 1991, issued 1994) for methods and apparatus in digital audio broadcasting and reception, and U.S. Patent No. 5,278,826 (filed 1991, issued 1994) covering similar digital transmission techniques. In 2000, USA Digital Radio merged with Lucent Digital Radio to establish iBiquity Digital Corporation, which consolidated expertise and licensing for the IBOC system now branded as HD Radio. iBiquity advanced the technology through extensive testing, including field trials of AM and FM IBOC systems in 2001 sponsored by the to evaluate performance and compatibility. Regulatory progress accelerated in 2002 when the (FCC) approved iBiquity's hybrid IBOC modes for voluntary use by AM and FM stations, enabling simultaneous analog and digital transmission during daytime hours initially, with full 24-hour authorization for FM following later that year. Early partnerships were crucial, with broadcasters like Clear Channel Communications (now ) collaborating closely with iBiquity on pilots and equipment integration starting in the early 2000s to prepare for deployment. Commercial implementation launched in 2003, marking the transition from testing to widespread adoption. The inaugural HD Radio broadcast occurred on January 7, 2003, from WDMK-FM in , , while stations in over 40 markets, including WWDC-FM in Washington, D.C., began regular HD transmissions as early adopters, offering improved audio quality and multicasting capabilities to listeners with compatible receivers. By late 2003, more than 280 stations across 100 markets had licensed the technology, laying the groundwork for national rollout.

Key Milestones and Evolution

In the , HD Radio experienced significant growth in adoption, particularly through integration with automotive manufacturers. By 2015, HD Radio receivers had become standard equipment in over 35% of new automobiles sold , marking a shift from optional add-ons to widespread inclusion across major models from brands like Hyundai, , and Subaru. This expansion was accompanied by an increase in broadcasting infrastructure, with over 2,000 stations offering HD Radio services by the end of 2015, enabling broader access to and multicasting channels. Entering the 2020s, key corporate and regulatory developments further shaped HD Radio's trajectory. The technology, originally developed by iBiquity Digital, was acquired by DTS in 2015 and subsequently integrated into Corporation following its 2020 merger with , positioning as the primary steward of HD Radio advancements. In 2020, the (FCC) authorized voluntary all-digital operation for AM stations using HD Radio, allowing broadcasters to eliminate analog signals for improved noise resistance and efficiency without requiring a full overhaul. This milestone addressed longstanding challenges in , such as interference, and paved the way for enhanced digital delivery. The year 2025 marked the 20th anniversary of HD Radio's commercial launch in vehicles in 2005, with Xperi highlighting its enduring automotive legacy amid evolving audio landscapes. According to Edison Research's Q2 2025 Share of Ear study, AM/FM radio—bolstered by HD capabilities—accounted for 56% of in-car audio listening time among Americans aged 13 and older, underscoring its dominance in vehicular environments despite competition from streaming services. Regulatory progress continued with the FCC's May 2025 rule update permitting asymmetric digital sidebands for FM HD Radio stations, including low-power FM operations, which allows for optimized power allocation between upper and lower sidebands to improve coverage and reduce interference. Equipment evolution supported these advancements, with transmitters from manufacturers like Nautel and GatesAir becoming integral to HD Radio deployments. In 2025, industry best practices guides emphasized optimized installation techniques for new and upgraded systems, including precise alignment for hybrid and all-digital modes to maximize signal reliability and listener reach.

Technology Overview

Core Principles and Signal Processing

HD Radio operates on the in-band on-channel (IBOC) principle, which embeds digital signals within the existing allocation of analog AM and FM broadcasts, thereby avoiding the need for additional and minimizing interference with adjacent channels. This approach places digital sidebands symmetrically above and below the analog carrier , confined within the primary channel bandwidth to ensure compatibility and protect legacy analog reception. At the core of HD Radio's signal processing is (OFDM), a modulation technique that divides the stream into multiple closely spaced orthogonal subcarriers, each carrying a portion of the signal to enhance robustness against multipath and interference common in terrestrial environments. (FEC) is integrated through convolutional encoding with variable coding rates, such as 1/2, which adds redundant parity bits to the data, allowing receivers to detect and correct transmission errors without retransmission. Additionally, interleaving reorders the encoded bits across time and frequency domains, spreading burst errors over a wider area to improve decoding reliability, with configurations tailored to the VHF fading characteristics for FM and MF for AM. In hybrid mode, the foundational operational configuration, the analog host signal occupies the central portion of the channel while sidebands are added on either side, enabling simultaneous of the same audio content in both formats without disrupting existing analog receivers. For FM, the primary channel spans 200 kHz, with primary main sidebands extending approximately \pm 70 kHz from the carrier (specifically, 69.041 kHz per sideband), as defined by the subcarrier allocation where the center of each subcarrier is given by fn=n×Δff_n = n \times \Delta f and Δf≈363.373\Delta f \approx 363.373 Hz, ensuring the total extension fits within the channel boundaries. Total sideband span=2×(N×Δf)\text{Total sideband span} = 2 \times (N \times \Delta f) where NN is the number of subcarriers per sideband (e.g., 191 for MP1 mode), limiting the overall bandwidth to under 200 kHz for hybrid operation. This structured allocation supports data rates up to 96 kbps in primary modes while maintaining .

Compatibility with Analog Broadcasting

HD Radio employs a hybrid in-band on-channel (IBOC) transmission system that simulcasts the primary analog audio signal alongside a digital enhancement on the same frequency, preserving the integrity of the existing analog broadcast for legacy receivers. The digital data is encoded in orthogonal frequency-division multiplexing (OFDM) sidebands positioned adjacent to the analog carrier, which fall outside the typical 15 kHz audio bandwidth and 75 kHz deviation limits of conventional FM or AM analog signals. As a result, non-HD Radio receivers, which lack the capability to decode these sidebands, perceive only the unaltered analog signal, ensuring seamless compatibility without requiring any modifications to traditional broadcasting equipment or listener devices. To mitigate potential interference from the digital sidebands to the host and neighboring stations, the (FCC) mandates strict power and spectral constraints. Digital sideband (ERP) is limited to up to -14 (decibels relative to the carrier) for primary sidebands and approximately -32 for secondary sidebands in FM hybrid mode as of 2025, with allowances for higher primary power up to -10 and asymmetric sidebands under updated rules; similar ratios apply for AM. These parameters, defined in the NRSC-5-E standard (2022) and FCC rules, restrict self-interference and adjacent-channel impacts, maintaining -to-noise degradation below 1 dB within protected contours while allowing broadcasters to enhance coverage without disrupting legacy service. The NRSC-5-E standard incorporates recent enhancements, including advanced service modes for higher capacity and formal support for asymmetric operation, with FCC rules updated in 2024 to facilitate these power increases. In digital HD Radio receivers, a fallback mechanism automatically transitions from the digital stream to the analog when signal quality deteriorates, such as due to multipath , weak , or excessive bit error rates. This blending process occurs seamlessly over a few seconds, prioritizing audio continuity by the while ramping up the analog, and reverts to digital once conditions improve, thereby safeguarding the against interruptions common in pure digital systems. Certification of HD Radio transmitters and receivers is overseen by iBiquity Digital Corporation (now part of ), through standardized testing protocols that verify compliance with interference limits, including adjacent-channel protection ratios and out-of-band emission masks. These evaluations, conducted by accredited labs like , involve simulated and real-world scenarios to measure digital-to-analog , ensuring that deployed systems do not exceed FCC thresholds for first-adjacent channel interference.

Transmission Techniques

AM HD Radio

AM HD Radio employs a hybrid mode that integrates digital signals within the existing analog AM framework on medium-wave bands, adhering to channel spacings of 9 kHz in regions like or 10 kHz in the United States to align with traditional allocations. In this configuration, the digital sidebands are positioned adjacent to the analog carrier, with primary sidebands (outer) extending from approximately 9.5 to 14.5 kHz above and below the carrier frequency, while secondary sidebands (inner) occupy positions from approximately 4.5 to 9.5 kHz; these utilize (QAM) combined with (OFDM) for robust data transmission. The digital signal's power is limited to 1-20% of the analog carrier's power—typically expressed as -20 to -7 —to reduce self-interference and preserve analog reception quality. This hybrid approach faces inherent challenges due to the medium-wave band's characteristics, including greater vulnerability to multipath interference from ground reflections and , which degrade integrity more than in higher-frequency bands. Consequently, audio data rates remain constrained, supporting broadcasts at around 20-40 kbps, prioritizing correction and over higher to maintain reliability in noisy environments. In response to these limitations, the (FCC) authorized all-digital AM operation in October 2020, enabling stations to fully replace analog signals on a voluntary basis through a simple notification process. This mode, designated as MA3 in HD Radio specifications, eliminates the analog carrier and extends primary sidebands similarly to hybrid operation but with enhanced power allocation across the 20 kHz channel for better noise immunity; an optional enhanced configuration adds secondary and tertiary sidebands to achieve 40 kbps throughput for full audio. Compared to hybrid, all-digital MA3 improves coverage range—extending daytime signals to the 0.1 mV/m contour and nighttime to half the noise-free —while supporting metadata and alerts without legacy compatibility constraints.

FM HD Radio

FM HD Radio operates within the standard 200 kHz FM broadcast channel allocation, utilizing a hybrid mode that superimposes digital signals onto the existing analog FM waveform for . In this configuration, the digital sidebands are positioned symmetrically on either side of the analog carrier, spanning approximately ±67 kHz to ±134 kHz from the center in basic hybrid mode, with extended modes reaching up to ±198 kHz, avoiding significant overlap with the primary analog audio spectrum that extends to about ±75 kHz. This placement enables higher data capacities compared to AM HD Radio, supporting bitrates of up to 96-150 kbps, which can accommodate multiple audio streams or additional services. The digital signal employs Coded (COFDM) modulation, with symbol rates ranging from 4.5 to 6.7 Msymbols/s depending on the service mode, facilitating robust transmission in multipath environments. This modulation scheme divides the s into up to 191 OFDM subcarriers per in the basic MP1 hybrid mode, allowing for up to four independent subchannels that can carry main program audio, secondary audio services, or data. The s are structured into primary, secondary, and tertiary segments, with the primary main s occupying the outermost frequencies (approximately ±129 kHz to ±198 kHz) at higher power levels, while inner secondary and tertiary segments ramp down in power gradually toward the to minimize interference. An optional asymmetric sideband configuration enhances flexibility, particularly for datacasting applications, by allowing the upper to transmit at a higher power level than the lower one—up to a 10 dB difference—while maintaining overall digital power limits. FCC regulations cap the total injected digital power at 4% of the authorized analog power (equivalent to -14 in extended modes, nominal -20 for MP1), ensuring no harmful interference to adjacent channels, with recent rules (effective November 20, 2024) permitting broader use of without prior approval for most stations. This power ramping and segmentation in the sidebands further reduces by concentrating energy away from sensitive analog reception areas.

Advanced Features

All-Digital Modes

All-digital modes in HD Radio represent a shift from hybrid analog-digital simulcasting to purely digital transmission, eliminating the to optimize use and enhance performance. These modes were developed to address limitations in traditional , particularly for AM stations susceptible to noise and interference, while offering potential expansions for FM. The (FCC) approved the use of all-digital operations for AM stations in October 2020 through the adoption of a Report and Order authorizing the HD Radio MA3 mode. The MA3 mode for all-digital AM broadcasting removes the analog carrier, confining the digital signal to a narrower bandwidth of approximately 10 kHz, which improves compared to hybrid modes. This configuration allows AM stations to transmit without the compromises required for analog compatibility, such as reduced digital power to avoid interference. Introduced as part of the FCC's efforts to revitalize AM radio, MA3 enables stations to operate without the blending delays inherent in hybrid systems, where receivers switch between analog and digital signals. By 2025, the FCC has continued to support digital enhancements, with rules permitting low-power FM (LPFM) stations to adopt HD Radio technology in hybrid mode, including asymmetric operations, to expand digital service . All-digital modes offer several key benefits over hybrid operations, including greater signal robustness against noise and interference due to the absence of analog vulnerabilities. Without interference from overlapping analog and digital signals, reception is more consistent, with no fade-in delays during signal transitions. Additionally, these modes support higher fidelity audio, approaching near-CD quality for AM and enabling multichannel formats such as , which enhances immersive listening experiences. As of late 2025, deployment of all-digital AM remains modest, with four full-time stations operating in MA3 mode (WSHE in Frederick, MD; WYDE in Birmingham, AL; WMGG in Tampa, FL; and one experimental), alongside ongoing tests like WNYC's planned full-power trial in New York. This limited transition reflects challenges in receiver availability, though from manufacturers like Nautel and GatesAir fully supports MA3 implementation through integrated exciters and transmitters. For FM, all-digital operation has seen negligible uptake, underscoring the preference for hybrid systems in that band.

Metadata and Enhanced Services

HD Radio's digital sidebands, particularly in FM implementations, support the transmission of non-audio metadata through Program Service Data (PSD), which enhances the listening experience by providing contextual information synchronized with the broadcast audio. PSD encompasses dynamic text and visual elements delivered to compatible receivers, allowing stations to convey details about the current program without interrupting the primary audio stream. This capability leverages the robust data channel inherent to the HD Radio system, enabling seamless integration of supplementary services. A key application of PSD is the Artist Experience feature, which delivers program-associated data such as song titles, artist names, and album artwork directly to receivers. This involves synchronous transmission of images—typically 200x200 pixels in or format, up to 24 KB in size—timed to align with audio segments, often triggered by XHDR frames for precise within 0.5 seconds of a new song. Receivers display this metadata, including paired with promotional text, enhancing user engagement; if images are unavailable, a fallback to the station logo occurs. Broadcasters are recommended to transmit images at least once per song, utilizing vendors like TagStation for implementation, with software requirements including Importer v4.3.1+ and HDP PSD SDK v4.7+. HD Radio also integrates PSD with the Emergency Alert System (EAS), enabling digital delivery of public warnings that offer advantages over analog methods, including faster alert speeds and high-precision geographic targeting. This allows for rapid dissemination of emergency information, such as weather alerts or evacuation notices, directly through the digital stream to HD-capable devices, complementing traditional EAS audio tones with enhanced reliability and coverage in FM sidebands. In a 2025 filing to the FCC, Xperi emphasized HD Radio's role in modernizing EAS by supporting quicker delivery compared to legacy analog systems. Additional PSD services include real-time updates, weather conditions, and station logos, which are transmitted as text or low-bandwidth visuals to inform listeners without requiring separate applications. For instance, partnerships like Mitsubishi's HD Radio Data Services provide dynamic and fuel price information, while station logos consume approximately 200 bps per program for display. These features operate within the FM sideband structure, which allocates up to 128 kbps for digital services when paired with mono analog signals, ensuring sufficient capacity for metadata alongside audio. In 2025, advanced metadata capabilities through the DTS AutoStage platform, which enhances HD Radio's integration in automotive systems by delivering consistent, rich visual metadata such as album art and artist details across FM and digital streams. This update builds on HD Radio's 20-year automotive legacy—reaching over 115 million vehicles worldwide—by improving synchronization and personalization in in-vehicle entertainment, without requiring subscriptions.

Comparisons to Other Standards

HD Radio versus DAB

HD Radio and Digital Audio Broadcasting (DAB) represent two prominent digital radio standards, with HD Radio employing an in-band on-channel (IBOC) approach primarily in North America, while DAB utilizes a dedicated spectrum model dominant in Europe and beyond. These differences stem from their design philosophies: HD Radio integrates digital signals within existing analog bands to facilitate a gradual transition, whereas DAB operates as a standalone digital system requiring separate infrastructure. HD Radio is a proprietary technology developed by iBiquity Digital Corporation (now part of Xperi), involving licensing fees, while DAB is an open international standard set by the European Telecommunications Standards Institute (ETSI), allowing royalty-free implementation. In terms of spectrum use, HD Radio transmits digital signals within the same frequency allocations as traditional AM and FM broadcasts, adding sidebands of approximately ±129 to ±198 kHz for FM without needing new , which enables efficient reuse of established bands. Conversely, DAB requires dedicated allocations, typically in the VHF (174-240 MHz) or L-band (1452-1492 MHz), using about 1.5 MHz per multiplex to support multiple channels, which demands regulatory assignment of new frequency blocks. Regarding compatibility, HD Radio's hybrid mode simulcasts analog and digital audio on the same channel, allowing existing analog receivers to function uninterrupted while providing enhanced digital options for compatible devices, thus supporting during adoption. In contrast, DAB operates as a clean digital system on separate frequencies, necessitating new receivers and spectrum reallocation, which eliminates analog support and requires a full overhaul for broadcasters and listeners. Both standards deliver audio quality comparable to CD levels, with HD Radio achieving near-CD stereo via codecs at 48-128 kbps for FM and DAB using MPEG Audio Layer II or AAC+ at 64-192 kbps, though HD Radio emphasizes multicasting for up to three subchannels (e.g., HD1, HD2, HD3) on a single frequency to expand programming options. DAB also supports multiple services within its multiplex but excels in mobile reception across Europe due to its orthogonal frequency-division multiplexing (OFDM) and robust error correction, providing more consistent coverage in dynamic environments compared to HD Radio's occasional signal blending between analog and digital. Adoption patterns highlight regional divergences, with HD Radio leading in the United States where over 2,500 stations broadcast in the format as of 2025, bolstered by integration in automotive systems from major manufacturers. DAB, however, prevails internationally in over 50 countries, particularly in with high coverage (e.g., over 97% in the UK) and widespread use in new vehicles, enabling broader global reach for digital-only services.

HD Radio versus DRM

HD Radio and Digital Radio Mondiale (DRM) represent two distinct approaches to digital terrestrial radio broadcasting, each tailored to different operational environments and priorities. HD Radio, developed primarily for the North American market, operates exclusively in the medium frequency (MF) AM band (535–1705 kHz) and VHF FM band (87.5–108 MHz), focusing on in-band on-channel (IBOC) transmission that overlays digital signals within existing analog channel allocations for local and regional coverage. In contrast, DRM is designed for a broader spectrum including long wave (LW, 150–285 kHz), medium wave (MW, 300–3000 kHz), shortwave (HF, 3–30 MHz), and VHF bands up to 174–240 MHz via its DRM+ mode, enabling robust long-distance and international broadcasting particularly suited to shortwave propagation for global reach. This frequency flexibility makes DRM especially valuable in regions with sparse infrastructure, where shortwave can cover vast areas without relying on dense networks of local transmitters. HD Radio's proprietary nature contrasts with DRM's status as an open standard endorsed by the International Telecommunication Union (ITU), facilitating easier adoption in international contexts without proprietary licensing. Both technologies utilize (OFDM) as their core modulation scheme to combat multipath interference and fading, but they differ in implementation and efficiency. DRM employs differential quadrature (DQPSK) for its DRM30 mode in lower bands and 4- or 16-quadrature amplitude modulation (QAM) for DRM+, optimized for lower bitrates typically ranging from 4 to 72 kbps to ensure reliability over noisy, long-haul channels with minimal power. HD Radio, on the other hand, uses higher-order QAM schemes (up to 64-QAM) to achieve bitrates up to 150 kbps in its FM mode, supporting higher-fidelity audio and multiple data services, though this comes at the cost of greater susceptibility to interference in hybrid operation. These modulation choices reflect their efficiencies: DRM prioritizes spectral economy and robustness for international use, while HD Radio emphasizes capacity for domestic multicasting. In terms of compatibility, HD Radio's hybrid mode analog and digital signals within the same channel, allowing seamless transition for legacy receivers but limiting digital capacity and causing potential , a design driven by U.S. regulatory requirements for maintaining analog service. DRM, being fully digital without mandatory analog , offers greater flexibility for developing regions by allowing complete spectrum reallocation to digital, though it requires new receivers and lacks , making it ideal for greenfield deployments in areas transitioning from analog shortwave. This all-digital approach in DRM supports single-frequency networks (SFNs) for efficient coverage but demands higher initial investment in receiver adoption compared to HD Radio's incremental rollout. Adoption patterns further highlight their divergent paths: HD Radio remains largely confined to , with widespread deployment in the U.S., , and , covering over 90% of markets but minimal international expansion beyond trials in countries like . DRM, endorsed by the (ITU), has seen broader global uptake for international and shortwave broadcasting in dozens of countries, including , , , , , , and , with recent 2025 adoptions such as 's national standard for domestic short- and medium-wave digital radio enhancing its role in emerging markets. While no widespread cross-compatibility has emerged between the standards, underscoring their regional silos.

Adoption and Challenges

Market Penetration and Coverage

As of 2025, HD Radio operates on over 2,500 stations across the , with approximately 90% of these being FM outlets, providing capabilities to a significant portion of the radio landscape. These stations cover about 90% of the U.S. population and account for 80% of total radio listening hours, with particularly strong penetration in major markets such as New York, where nearly all full-power FM stations offer channels via HD Radio. In the top 50 Nielsen markets, around 750 stations broadcast in HD Radio, enabling access to over 4,500 digital subchannels nationwide. Automotive integration has been a key driver of HD Radio's reach, with the technology standard in 60% of new vehicles shipped in the U.S. in 2024, contributing to AM/FM radio's dominance in in-car listening. According to Edison Research's Q2 2025 Share of Ear study, AM/FM radio, including HD Radio-enabled signals, captures 56% of all in-car audio time across the U.S., regardless of ad presence. Globally, HD Radio is integrated into 115 million vehicles as of 2025, reflecting widespread adoption by 25 major car brands. Internationally, HD Radio adoption remains limited primarily to and , where it supplements U.S. border signals and supports local stations, though no widespread deployment has occurred in due to the prevalence of DAB standards. In , select FM stations in markets like broadcast HD Radio channels, while features over 200 digital channels on more than 100 stations, concentrated near the U.S. border. Trials continue in , where HD Radio is under consideration as a digital standard alongside DRM, and in , though progress has been slow with no confirmed operational stations as of 2025. HD Radio's growth in the U.S. has been steady since its commercial launch, expanding from around 100 stations in to the current network of over 2,500, driven by automotive demand and opportunities. For , all-digital HD Radio modes—eliminating analog simulcasts for improved efficiency—operate on a small number of stations (approximately four as of 2025), including experimental and authorized implementations that enhance signal robustness in challenging environments.

Criticisms and Limitations

One major criticism of HD Radio centers on its audio quality, particularly for subchannels, which often suffer from dropouts during mobile reception due to the lower power allocation for digital sidebands compared to the primary . These dropouts occur because the digital signal requires a stronger reception threshold, leading to abrupt interruptions when the receiver loses the HD signal while the analog backup remains audible, frustrating listeners in vehicles where signal fluctuations are common. Additionally, the lower bitrates used for subchannels—typically 48–64 kbps—introduce compression artifacts such as audible and reduced high-frequency detail, especially on dynamic content like music, where heavy exacerbates intermodulation issues. In hybrid mode, where HD Radio overlays digital signals onto existing analog broadcasts, interference degrades the traditional analog reception for legacy radios lacking HD tuners. This manifests as a noticeable "digital hiss" or noise on the analog signal, stemming from unintentional emissions and intermodulation products from the digital carriers that encroach on the FM or AM host frequency. On AM stations, the interference potentially reduces analog coverage and contributes to listener complaints about static or muffled audio. Economic barriers further limit HD Radio's appeal, especially for smaller broadcasters, as implementing the technology requires significant upfront investment in equipment, with transmitter upgrades typically costing $30,000–$150,000 per station, depending on power and setup. Royalties and licensing fees from add to the burden, including a one-time payment (e.g., $5,000 for non-commercial stations) plus potential revenue-based royalties for multicasting, and ongoing per-chipset royalties of $3 for receivers, which deter low-power or stations from adopting the system due to uncertain returns on subchannel programming. Moreover, hybrid operation can increase power consumption, elevating electricity costs and straining budgets for stations already operating on thin margins. Compatibility issues arise from the inconsistent implementation of subchannel formats across stations, where varying bitrates and audio modes (e.g., stereo vs. parametric stereo) result in unpredictable quality and tuning experiences for listeners. This lack of confuses users, as subchannels may switch between , talk, or data services without uniform receiver handling, leading to fragmented listening. By 2025, reports highlighted growing rejection of AM hybrid modes, with consumers and even some automakers citing poor performance and interference as reasons for phasing out support in favor of all-digital alternatives or streaming. As of late 2025, some automakers like have discontinued HD Radio in new models, citing low consumer demand.

Programming and Distribution

Multicasting and Subchannels

HD Radio's multicasting feature enables FM broadcasters to transmit multiple independent audio streams, known as subchannels, within the same , thereby expanding programming options without the need for additional licenses. The primary subchannel, designated , simulcasts the station's analog FM signal in digital format for improved audio quality and compatibility with legacy receivers. Additional subchannels, such as HD2, HD3, and up to HD4, allow for supplementary content like niche music genres (e.g., on HD2) or talk programming on HD3, with a maximum of three secondary program services (SPS) beyond the main program service (MPS). This capability leverages the digital sidebands to divide the available efficiently. The digital bandwidth for FM hybrid mode typically ranges from 96 to 120 kbit/s, allocated across subchannels to balance capacity and quality. The subchannel commonly operates at 64-96 kbit/s to deliver near-CD-quality audio, while secondary subchannels like HD2 and HD3 are assigned lower rates of 24-48 kbit/s, sufficient for mono or compressed formats suitable for talk or specialty programming. This allocation supports diverse content delivery, such as artist experience features or , without exceeding the total bandwidth constraints. Major broadcasters, including , extensively employ to enhance audience engagement and reach underserved demographics. As of 2024, operates HD Radio on approximately 388 stations across its network—a majority of HD stations utilize —utilizing HD2 and HD3 for targeted formats like programming or dedicated networks for genres such as , thereby increasing overall listenership without additional infrastructure costs. This strategy has contributed to the growth of over 2,200 active channels nationwide. Despite these advantages, multicasting involves trade-offs in audio due to bandwidth sharing, where allocating bits to multiple subchannels reduces the bitrate available for each, often resulting in lower on secondary streams compared to HD1. Subchannels at 24-48 kbit/s may exhibit compression artifacts or limited , particularly for music, prioritizing content variety over pristine audio reproduction in bandwidth-constrained setups.

Translators and Signal Boosters

HD translators function as low-power FM repeaters designed to rebroadcast secondary subchannels, such as HD2 and HD3, from primary HD Radio stations, thereby extending the reach of digital programming without requiring full-power facilities. These translators operate at effective radiated powers () up to 250 watts, in line with FCC limits for FM fill-in services, and convert the digital HD signal to an analog format for broader compatibility with existing receivers. The authorized this practice in May 2010, ruling that analog FM translators could rebroadcast HD digital channels from commonly owned primary stations, provided they do not originate independent programming. Signal boosters, in contrast, serve as on-channel that amplify and retransmit the primary station's HD Radio signal on the same to bolster coverage in fringe or shadowed areas, such as urban canyons or rural terrains prone to signal attenuation. To prevent self-interference, boosters incorporate deliberate in the signal path—typically matching the propagation time from the main transmitter—ensuring coherent reception and minimizing multipath that could degrade fidelity. FCC regulations permit boosters as long as they do not cause interference to the primary signal or adjacent channels, with requirements emphasizing precise and power control to preserve the HD Radio waveform's integrity. Numerous HD-fed FM translators are in operation across the , particularly valued for enhancing rural coverage where primary signals may weaken due to or distance, allowing stations to deliver subchannel content to underserved communities. These translators integrate seamlessly with HD Radio's hybrid mode but also support transitions to all-digital operations on compatible primary stations, such as all-digital AM, by maintaining signal consistency without introducing analog degradation. Regulatory oversight mandates that translators preserve HD fidelity during rebroadcast, prohibiting purely analog configurations for exclusively digital content to ensure listeners receive the intended digital quality benefits.

Receivers and Implementation

Automotive and In-Vehicle Systems

HD Radio has become a standard feature in a significant portion of new vehicles in the United States, with nearly 60% of models sold in equipped as of . Major manufacturers such as Ford and have integrated it since 2007, making it available across a wide range of their lineups including sedans, SUVs, and trucks. The technology marked its 20th anniversary of commercial automotive deployment in , reaching over 115 million vehicles worldwide and underscoring its evolution into an industry staple for in-vehicle audio. Key features of HD Radio in automotive systems include seamless tuning between primary channels (HD1) and multicast subchannels (HD2, HD3, etc.), allowing drivers to access additional programming without manual intervention once a digital signal is detected. Integrated infotainment displays show real-time metadata such as song titles, artist names, and album artwork directly on the dashboard, enhancing the user experience during drives. Compatibility extends to hybrid and electric vehicles, with models like the 2026 Toyota C-HR battery electric vehicle and various Ford EVs incorporating HD Radio receivers alongside other audio options. Performance in mobile environments benefits from HD Radio's time diversity techniques, which introduce a delay between analog and digital signals to maintain audio continuity during brief signal interruptions common in driving scenarios. Many modern vehicles employ diversity antenna systems—typically two or more antennas positioned for optimal coverage—to improve overall reception, including for HD signals, reducing multipath in urban or highway settings. This contributes to AM/FM radio's dominant 56% share of in-car audio consumption among U.S. drivers, as reported in Edison Research's Q2 2025 Share of Ear study. Despite these advances, challenges persist, particularly subchannel dropouts in densely populated urban areas where signal interference can cause intermittent loss of digital multicasts. By 2025, ongoing firmware updates in select infotainment systems have aimed to mitigate these issues through enhanced and faster blending between analog and digital modes, though reception quality can still vary by location and configuration.

Home, Portable, and Professional Devices

Home HD Radio receivers are primarily available as dedicated tuners or tabletop units designed for integration into systems, rather than built into mainstream AV receivers from brands like or Yamaha, which discontinued native HD Radio support in favor of streaming around 2015. Models such as the HDT-20 and ViewQuest tuners connect via analog or digital outputs to setups, delivering while supporting subchannels for additional programming streams and displaying metadata like song titles, artist names, and album art on integrated screens. These devices enhance traditional AM/FM reception with HD Radio's digital signal, providing interference-free listening and emergency alerts, though they require external antennas for optimal performance in fringe areas. Portable HD Radio devices cater to on-the-go listening with compact, battery-powered designs that emphasize durability and extended runtime. The HDR-16 stands out as a lightweight handheld unit supporting both analog and digital HD Radio reception, including channels and metadata display for program information. Powered by four C-size batteries, it offers approximately 20 hours of operation at moderate volume levels, making it suitable for travel or outdoor use, though its internal antenna may necessitate an external one for weak signals. Smartphone integration remains limited, with no native over-the-air HD Radio tuners in mobile devices; instead, apps like the HD Radio app provide streaming access to select stations but do not receive broadcast signals directly. Professional HD Radio equipment focuses on broadcast infrastructure, enabling stations to transmit high-quality digital signals efficiently. Exciters from manufacturers like GatesAir, Nautel, and Broadcast Electronics integrate HD Radio technology, allowing for hybrid analog-digital or all-digital modes as of 2025 models, which support increased power levels up to 10 dB for better coverage without interfering with analog signals. Xperi's licensed HD Radio platform powers these devices, facilitating studio-to-transmitter links, signal monitoring, and multicasting for up to four subchannels per station. Studio monitors compatible with HD Radio, such as those from Inovonics, provide real-time audio quality checks during production, ensuring compliance with digital standards. As of 2025, standalone HD Radio device sales have declined amid the rise of streaming services, which captured 30% of ad spend and drove overall radio listening shifts, though HD Radio maintains a niche in vehicles and broadcaster tools with over 2,300 U.S. stations transmitting digitally. Bundling in smart speakers remains rare, limited to select models with streaming apps rather than native OTA reception.

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