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HD Radio is the registered trademark for the in-band on-channel (IBOC) technology selected by the Federal Communications Commission (FCC) in 2002 for terrestrial digital audio broadcasting in the United States. The IBOC technology was developed by iBiquity Digital Corporation, and it allows stations to simulcast HE-AAC-quality compressed digital audio and traditional analog audio, without changing to new frequency bands. The specification for this standard offers two operating modes: "All Digital" and "Hybrid Digital". According to iBiquity, the name "HD Radio" is simply iBiquity's brand for its digital radio technology, however according to the HD Radio Alliance the HD means Hybrid Digital.

As of 2007, more than 1200 AM and FM stations are broadcasting with HD Radio technology, with more than 550 FM stations offering more than one digital channel per FM frequency, thus doubling or tripling the number of programs available to listeners. Most of the stations that have adopted the technology are FMs, while AM stations have been slower to upgrade. As with traditional AM, FM and TV broadcasting, HD Radio programming is free and supported either by commercial advertising or public broadcasting. However, as is the case with the new ATSC DTV standards, consumers must upgrade to a new receiver in order to receive the digital broadcasts. Brand name HD Radio receivers are available for home and car at major consumer electronics chains, online and through regional stores.

Other in-band on-channel digital radio competitors include FMeXtra, Digital Radio Mondiale (DRM+), and Compatible AM-Digital (CAM-D) developed by the inventor of AM Stereo, Leonard Kahn.

Overview

Digital information is transmitted using COFDM, a modulation method that has been used in different digital television and radio systems, including DVB-T. The audio compression algorithm was initially set to be PAC when iBiquity's standard was first approved by the FCC in 2002, but the system was changed to HDC with SBR in 2003 (based upon MPEG-4 HE-AAC). HD Radio equipped stations must pay annual royalties to iBiquity, and costs paid by the manufacturers of HD transmitters that are passed along to the purchaser.

NDS, a maker of digital media encryption technology, recently signed a deal that effectively institutes subscriptions capability on digital radio. "RadioGuard is based on NDS’ industry-leading VideoGuard technology already deployed in more than 70 million digital set-top boxes worldwide ... enabling pay-per-listen, opt-in, and public service offerings on the HD Radio platform." NDS says this system will allow listeners to listen to live concerts or events, via paying a small fee, similar to how Pay Per View events operate with television.

While in hybrid digital/analog mode, an HD Radio will lock onto an analog signal first in mono, then stereo, then try to find a digital signal. If digital signal reception is lost, the radio will revert to the analog signal. Much of the success of this system capability relies on proper time synchronization of the analog and digital audio signals by broadcast engineers maintaining the transmitter. If in the future the FCC decides to discontinue analog radio, as they have with analog television, then the HD Radio is designed to revert to a very-low-speed ~20 kilobit per second stream. Datacasting is also possible, and RDS-like metadata providing song titles or artist information are included in the standard. Transmitting multiple digital channels per FM channel is also possible; these are called "Multicast" channels in HD Radio terminology (although this means something different from the normal meaning of multicast, and could be more properly described as multiplexing).

iBiquity Digital claims that the system approaches CD quality sound and offers reduction of both interference and static; however, many listeners have complained of increased interference on the AM band (see AM, below). In March 2007, the FCC approved a nationwide rollout of HD radio technology While iBiquity is responsible for the development of these standards, and the FCC for its regulation, the National Radio Systems Committee (NRSC) is the standards body for HD Radio. The HD Radio standard is officially known as NRSC-5, with the latest version being NRSC-5A. As of Spring 2007, fewer than 500,000 HD radios have been sold in the U.S.; terrestrial broadcasters are hopeful that a large marketing campaign and falling prices for HD Radio receivers will increase sales.

AM

Sending pure digital data through the narrow 10 kilohertz AM channel is roughly equivalent to sending data through an analog telephone line (~33.6k), thus limiting the maximum throughput possible. By using Spectral Band Replication the HDC+SBR codec is able to recreate sounds equal to or exceeding 15,000 Hz, thus achieving FM quality on the bandwidth-tight AM band. HD Radio's AM hybrid mode offers two options which can carry approximately 40 or 60 kbit/s of data, but most AM-digital stations default to the more-robust 40 kbit/s mode which features redundancy (same signal broadcast twice). If in the future the FCC decides to discontinue analog radio, as they have done with analog television, the HD Radio provides a pure digital mode. In this mode the AM station lacks an analog signal for "fall back", and instead reverts to a low-quality 20 kbit/s signal during times of poor reception.

The AM version of HD Radio adds 10 kHz to each side of the center frequency, meaning that the entire signal is 30 kHz (three full channels) wide, and overlaps one adjacent channel on both sides. Some nighttime listeners have expressed concern this design harms reception of adjacent channels.; in fact, at least one formal complaint has been filed regarding the matter: WYSL owner Bob Savage, arguably the most vocal opponent of HD Radio on the AM band, filed a complaint against WBZ in Boston. WBZ (a 50,000 watt station on the 1030 kHz frequency), Savage alleges, was causing interference to Savage's 500 watt night signal at 1040 kHz.

When operating in pure digital mode, the AM-HD signal fits inside a standard 10 kHz channel (20-40 kbit/s) or an extended 20 kHz channel (40-60 kbit/s), at the discretion of the station manager.

Most analog AM radios have filtering in the IF stage to narrow the bandwidth to less than the 10 kHz channel, but some "wideband" receivers do not filter this way, making the encoded signal audible. However, on most AM radios, it is possible to hear the digital sidebands by tuning above or below the desired frequency. iBiquity's standard is incompatible with C-QUAM AM stereo broadcasts.

FM

The FM hybrid digital/analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of lossy data depending upon the Station Manager's power budget and/or desired range of signal (achieving perceived quality equal to a 1400 kbit/s CD). If in the future the FCC decides to discontinue analog radio, as they have done with analog television, the HD Radio provides several pure digital modes. In these modes broadcasts can be made at 270 or 300 kbit/s maximum, with extra features like surround sound. Like AM, pure digital FM provides a "fall back" condition where it reverts to a low-quality 25 kbit/s signal in the event of interference.

FM stations have the option to subdivide their datastream into sub-channels (FM97-HD1, -HD2, -HD3) of varying audio quality. The multiple services are similar to the sub-channels found in ATSC-compliant Digital Television using multiplexed broadcasting. For example, National Public Radio plans to carry several different streams, calling its proposed addition to the FM standard "Tomorrow Radio". Meanwhile some Top 40 stations have added Hot AC and Classic Rock to their sub-channels to provide more variety to listeners. Stations may eventually go all-digital, thus allowing as many as three full-power channels and four low-power channels (seven total). As defined by iBiquity these channels could be sub-divided into CD-quality (100 kbit/s), FM-quality (25-50 kbit/s), AM-quality (12 kbit/s), or Talk-quality (5 kbit/s) channels.

Bandwidth

Currently, FM stations in the United States and Canada are licensed to carry 130 kilohertz of audio modulation bandwidth, requiring approximately 260 kilohertz of RF spectrum. Only 15 kHz of the modulation bandwidth is used by analog Monaural audio. Analog stereo uses 53 kHz of space, and RBDS is centered at 57 kHz. The "remainder" is currently available for other services, including rental for secondary broadcast services, paging and datacasting, radio reading service, or as a transmitter-studio link for in-house telemetry.

In regular hybrid mode, a station has its full ± 130 kHz of analog bandwidth, and adds an extra ± 70 kHz for its digital signals, thus taking a full 397 kHz of width. In extended hybrid mode, the bandwidth of the FM signal is reduced to make way for additional OFDM carriers carrying more data. Because of this, FM stations may have to discontinue existing subcarrier services (usually at 92 kHz and 67 kHz) in order to carry extended HD Radio, though such services can be restored through use of the digital subchannels that are then made available. Also, the option is available to discontinue analog stereo encoding, further freeing up bandwidth. Eventually stations could elect to drop the analog audio completely and go all-digital. However, considering that there are billions of existing analog-only receivers, this is not expected to happen in the immediate future.

As with AM, FM stations may use separate exciters to modulate the very different signals. A combiner is often used, either before common amplification or after separate amplification, though stations are also now allowed to use a separate transmitting antenna slightly higher or lower on the radio tower. In each case the ratio of power of the analog signal to the digital signal is standardized at 100:1. The 1% power level of the digital signal from FM stations is sufficient to approximate the coverage area of the analog signal. Going forward, advances in digital tuner design will create the scenario where the digital signal coverage will probably exceed the analog coverage due to the greater potential ability to extract digital information from a noisy signal. The National Association of Broadcasters (NAB) is expected to request a 10 dB increase in the digital signal from the FCC. This equates to a tenfold increase in digital power. Although not FCC approved yet, the option exists for stations to deploy a Single Frequency Network (SFN), whereby a station can locate extra FM transmitters, on the same frequency, in poor reception areas within their market area. This option would be available only when stations have discontinued their analog service, as digital radio is significantly immune to multipath interference. As an interim measure, an On Channel Digital Repeater would achieve the same objective without interfering with the FM analog signal .

There are still some concerns that HD Radio on FM will increase interference between different stations, though it is thought unlikely to make a major difference since HD Radio still fits within the existing spectral mask, and the digital portion is only 1% of the main FM power level. An HD Radio station will not generally cause interference to any analog station within its 1 mV/m signal strength contour, the limit above which the FCC protects most stations. A distinct possibility exists of interference between HD stations in neighboring markets, which may be assigned frequencies only one or two channels apart.

Comparison to EU's Digital Radio

FM-HD Radio versus DAB

Most European Union states have implemented Digital Audio Broadcasting (DAB), with compatible radios hitting shelves in 1999. DAB broadcasts a single station that is approximately 1500 kilohertz in width (~1000 kilobits per second). That station is then subdivided into multiple digital streams of between 9 and 12 programs. In order to implement DAB, it was necessary for the European Telecommunications organization to set aside a new range of frequencies, whereas FM-HD Radio shares its digital broadcast with the traditional 200 kilohertz-wide channels.

AM-HD Radio versus DRM

The European Union states are in the process of rolling-out Digital Radio Mondiale (DRM), with compatible radios already available for sale. DRM is very similar to AM-HD Radio in that each station is broadcast via a channel 10 kilohertz wide, and the radio is hand-tuned to each individual station's location on the dial. The two standards also share the same modulation scheme (COFDM), the same compression-decompression standard (MPEG-4 AAC+), and like HD Radio, DRM allows broadcasters multiple options:

• Hybrid mode (digital/analog) — 10 kHz analog plus 5 kHz digital at ~10 kbit/s
• Single-wide (digital only) — 10 kHz digital at ~25 kbit/s — (HDR is 20-40 kbit/s)
• Double-wide (digital only) — 20 kHz digital at ~55 kbit/s — (HDR is 40-60 kbit/s)

Actual DRM bit rates vary depending on day versus night transmission and desired robustness.

DRM offers a growth path for broadcasters to first broadcast a hybrid digital/analog signal, and then later phase out the analog signal. Unfortunately DRM shares many of the same flaws as DAB and HD Radio: Shorter broadcast distance as compared to analog AM signal when in hybrid mode (note that in all-digital mode the digital signal is increased by 15 dB, a 32-fold increase in the digital power); radios that are overly expensive; poor reception inside vehicles and buildings; and interference with adjacent channels (15 kHz hybrid mode does not fit in the 10 kHz channel) — but in all-digital mode these interference issues cease.

Criticisms

Awareness, expense, coverage

There is low awareness amongst consumers in the new Digital HD Radio. According to a survey by Bridge Ratings, when asked the question, "Would you buy an HD radio in the next two months?" only 1.0% responded "yes". Some engineers have also expressed distrust or dislike of the new system.

Unlike regular car radios, which come fitted as standard equipment with virtually all automobiles, HD Radio requires consumers to purchase a new radio costing just over $100. HD Radio tuners for the home cost $75 and up. As of November 2007, a stereo HD component that can be linked into an existing home stereo system, such as the Sangean HDT-1X, costs approximately $250 for the tuner alone, without its own amplifier or speakers. The very high cost of stereo HD units in comparison with regular radio receivers, possibly caused by the single source and proprietary nature of the iBiquity chipset, appears to have stalled consumer adoption in the United States.

Most of the first generation HD Radio tuners have been noted as being very insensitive, making reception problematic. In hybrid mode, the HD Radio signal is 1/100th the power of a station's analog signal. Due to its relative weakness, the HD Radio signal will sometimes drop out and the receiver will revert to analog mode. This can be especially problematic in fringe areas, where the digital signal may frequently be lost. If the digital stream on a secondary (HD2, HD3, etc.) channel is different than the analog broadcast, then any time the digital signal fades out the receiver output switches to whatever program is broadcast on the analog signal. While this is by design and is part of the HD specification, it can be very annoying to the listener, who may perceive the station to have been randomly changed. In addition it has been noted that the analog section of some tuners displays poor reception capabilities compared to older non-digital models.

Proprietary & incompatible

HD Radio is a different digital broadcasting standard than those previously adopted by other countries. The lack of a common standard means that digital radios of one country may not work in another, and that manufacturers must develop separate products for different countries. As a result, costs are raised for both broadcasters and consumers. International standards that compete against HD Radio include the Eureka-147 Digital Audio Broadcasting ("DAB") system (see "Regional implementations of DAB" in Digital Audio Broadcasting), its newer variant "DAB+" (see "DAB+" in Digital Audio Broadcasting), and Digital Radio Mondiale, ("DRM", not related to Digital Rights Management). DAB (ratified by the ITU-R standardization body in 1994) has been selected for use by many countries on VHF and higher frequencies, where sufficient bandwidth may be allocated for high-quality sound on many program streams. DRM (ITU ratified April 2001) is, at least initially, intended for use at frequencies below 30 MHz, in traditional medium wave ("AM") and short wave bands. ETSI publishes the standards for DAB and DRM.

The HD Radio audio Codec, called "HDC", is incompatible with the DAB and DRM audio codecs, AAC and HE-AAC. Whereas the AAC (Advanced Audio Coding) family of codecs are publicly documented standards, and implemented on hundreds of diverse non-radio related devices and in computer software, the HDC codec exists only within the HD Radio system, and is an iBiquity trade secret.

Whereas DRM and DAB are controlled by non-profit consortiums with members from more than 30 countries, iBiquity ultimately has control over HD Radio receiver-manufacturer licensing and broadcaster licensing. Unlike DRM and DAB, which are open specifications, iBiquity's HD Radio specification is partly open and partly secret.

HD Radio has been officially adopted only by the U.S. and Brazil. iBiquity has stated in PR articles that countries evaluating HD Radio include Canada, France, Mexico, New Zealand, the Philippines, Switzerland, and Thailand. Canada adopted the Eureka-147 DAB standard in the late 1990s, but as of mid-2007 is exploring other options, including IBOC and DRM. In late 2006, the Canadian Radio-Television and Telecommunications Commission (CRTC) proposed allowing HD Radio to enter Canada’s digital radio broadcasting arena. In its Public Notice CRTC 2006-160, the Commission said it would be prepared to authorize services using the IBOC/HD Radio technology for the AM and FM bands if the Canadian department of Industry authorizes it under the Radiocommunication Act. The CRTC added that “an expedited process would be adopted for stations that propose to transmit a digital simulcast of their analog service.” However, a recent technical report from the Digital Radio Co-ordinating Group (DRCG) concluded, "Based on the evidence currently in hand, the DRCG considers that it would be risky for Canadian broadcasters to proceed at this time with an unrestricted roll-out of HD Radio services in the FM band, in the manner implemented in the US." As of mid-2007, Switzerland has officially selected, or is also testing, the Digital Audio Broadcasting standard, and France has already chosen DAB. iBiquity and other sources do not explicitly state in published articles what technically comprises the "evaluation", whether there are ongoing or elapsed test transmissions, and the quantity or power of transmitters.

In 2007, CFRM-FM from Little Current, Ontario is believed to be one of the first radio stations in Canada to broadcast in HD Radio.

In 2002, the U.S. FCC selected HD Radio as the U.S. digital radio broadcasting standard., even though it had no provision for compatibility with the DAB or DRM standards, which had each already been ratified by the International Telecommunication Union. Unlike subscription-based satellite radio, the content of HD Radio stations is subject to FCC regulation.

Reduced quality concerns

Promotion for HD Radio does not always make clear that some of its capabilities are mutually incompatible with other of its capabilities. For example, the FM system has been described as "CD quality." The FM system also allows multiplexing the data stream between two or more separate programs. However, 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. Indeed, the FCC "decline to require broadcasters to dedicate a minimum level of digital bandwidth to provide a high quality digital signal," however "one free over-the-air digital stream of equal or greater quality than the station’s existing analog signal." (If the FCC ever allows stations to discontinue analog simulcasting, each station will have over 300 kbit/s bandwidth available, allowing for CD or even Surround Sound-quality audio together with multiple sub-channels.)

Another such conflict arises from the extra "free" programs available today. iBiquity is seeking FCC approval for "conditional access," that is, enabling the extra programs to be available only by paid subscription (on future models of HD Radio). NDS, a maker of digital media encryption technology, has a deal with iBiquity to provide HD Radio with an encrypted content-delivery system called RadioGuard. NDS claims that RadioGuard will "provide additional revenue-generating possibilities." iBiquity has stated that RadioGuard will become a standard feature of the HD Radio system.

These competing capabilities mean that purchasers of early models of HD Radio have no guarantees of continued broadcasts of either high-quality audio or extra channels. Audio quality will suffer as broadcasters decide to subdivide their streams into extra "HD-2" and "HD-3" channels. And if the extra channels become subscription channels, they will become invisible to older radios without RadioGuard (and to those unwilling to pay for them).

Programming

Currently the HD Digital Radio Alliance, a consortium of major owners such as ABC, CBS, and ClearChannel that covers approximately 80% of the United States, has urged its members to broadcast multiple programs without radio commercials on the extra HD2 or HD3 sub-channels for a period of at least 18 months (ending sometime in 2007). Clear Channel is selling programming of several different music genres to other competing stations, in addition to airing them on its own stations.

The HD Digital Radio Alliance is also acting as a liaison for stations in a market to choose unduplicated formats for the extra channels (HD2, HD3, etc.). This is designed to provide additional choices for listeners instead of several stations all independently deciding to create the same format.

Some stations are also simulcasting their local AM stations on FM HD Radio sister stations. An example of this is Atlanta's WSB AM 750 being simulcast in stereo on WSRV FM's HD2 channel. It is common practice to broadcast a former FM station's format on its HD2 channel, such as WPGB in Pittsburgh, Pennsylvania, which carries the smooth jazz format on its HD2 band. This station was once known as WJJJ. WNNX/Atlanta also broadcasts its old format, 99X, on 99.7 HD-2. Likewise with WHDR/Miami, Florida, who brought "Party 93.1" and its Dance format back on its HD-2 channel.

Other recent additions include introduction of air staff on HD2 stations, like KDWB's Party Zone channel in Minneapolis-Saint Paul. This latest move seems to indicate that once the 18-month grace period ends, the broadcasters will start adding local content, including DJs and advertising, to the HD-2 stations.

Also of note in late 2007, Cincinnati's WVXU began simulcasting Internet radio station WOXY.com as an HD-2 station. This move marked the first time WOXY.com programming had been available over Cincinnati terrestrial airwaves in over 3 years.

Receivers

iBiquity's website has an online guide to the radios currently available.

Automotive

Receivers are becoming less expensive, starting at around US$100. Manufacturers have initially focused on making car stereos. In 2006, BMW began offering HD Radio tuners as an option in their 5, 6 and 7-series models. Starting in 2007, HD Radio tuners were also available as an option in all BMW vehicles and most MINIs.

In 2008, Ford Motor Company became the first U.S. automaker to feature HD Radio tuners in its vehicles; currently, HD Radio is a dealer-installed option on Ford, Lincoln and Mercury models. Beginning with the 2009 model year, Ford will offer HD Radio tuners as a factory-installed option.

• Alpine Electronics TUA-T500HD tuner module for Alpine receivers only
• HD DICE universal add-on tuner for factory radio integration, currently the only one available, but has been on perpetual "2-week back order" from the manufacturer since January 2008.
• Directed Electronics DMHD-1000 universal add-on tuner, requires the use of an included external screen. It can be used with your existing stock OEM or after market stereo.
• Dual XHD6420 receiver
• Dual XHD6425 receiver
• Jensen HD5212 receiver
• JVC KD-HDR1 receiver
• JVC KD-HDR30 receiver
• JVC KD-HDW10 receiver
• Kenwood KTC-HDR1 add-on tuner
• Pioneer GEX-P10HD add-on tuner, compatible with 2007+ head-units only
• Sony XT-100HD add-on tuner
• Visteon HD Jump dockable tuner universal add-on tuner
• Visteon HD Zoom add-on tuner kit universal add-on tuner

Home/Office and Professional

Home and office listening equipment is currently available from several companies, in both component tuner and tabletop models.

Portable

Until now, portable HD Radio receivers have been unavailable because the chipsets needed by this technology required 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 iPod-sized portable receiver. It is based on a new chipset developed by Samsung. Although portable, it is still a relatively power-hungry device (it will run out an average set of alkaline batteries in about two hours, according to an iBiquity engineer). But Samsung engineers at CES say a second-generation chipset due in 2009 will be about 40 percent more power efficient and then a third-generation chipset due about a year later will use even less energy. According to iBiquity, Sony and others have expressed an interest in using the first-generation chipset and that the first portable HD Radios could be on the retail market in the USA as early as Christmas 2008.

References

1. http://fjallfoss.fcc.gov/edocs_public/attachmatch/FCC-02-286A1.txt
2. iBiquity Digital Corporation - Trademarks
3. Screen snapshot of email from HD Digital Radio Alliance spokesperson Diane Warren confirming HD means "hybrid digital" at http://www.geocities.com/videonovels/HDradiomeans.GIF
4. ^ FCC approves HD Radio Rules, from Mediaweek
5. AM IBOC Stations on the Air
6. DIYmedia.net News Archive: April 2007
7. Press Release: http://www.nds.com/newspdfs/NAB_RadioGuard_iBiquity_160407.pdf
8. DIGITAL TELEVISION (DTV) Tomorrow's TV Today!
9. iBiquity Digital Corporation - IBOC White Papers
10. HD Digital Radio | DISCOVER IT! | How does HD Digital Radio Sound?
11. HD Radio Pumps Up Volume - Entertainment - RedOrbit
12. SBR explained: http://www.codingtechnologies.com/products/sbr.htm
13. DIGITAL TELEVISION (DTV) Tomorrow's TV Today!
14. Write or Karl me!: Night of the Bees
15. MP3 sample of the interference: http://www.wysl1040.com/media_files/wysl/IBOC_OBSERVATIONS.mp3
16. iBiquity Digital Corporation - IBOC White Papers
17. DIGITAL TELEVISION (DTV) Tomorrow's TV Today!
18. http://www.ibiquity.com/hd_radio/hdradio_find_a_station/MD/StnMarket#stationlist
19. iBiquity Digital Corporation - IBOC White Papers
20. What's New At Bridge Ratings
21. WYSL 1040 AM
22. Stop IBOC Now!
23. "HD Radio Undermined by Weak Tuners".
24. ^ "HD Rollout (author: iBiquity marketing)". 2006-04-11. Retrieved 2007-01-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help) Cite error: The named reference "Eda Geek" was defined multiple times with different content (see the help page).
25. "Petition for Reconsideration of Jonathan E. Hardis (Before U.S. FCC)". 2007-07-09. Retrieved 2007-10-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
26. ^ "Brazil Hosts HD Radio Rollout (author: iBiquity marketing)". 2006-11-01. Retrieved 2007-01-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help) Cite error: The named reference "Digital Radio News" was defined multiple times with different content (see the help page).
27. Welcome to HD Radio™
28. "Digital Radio Broadcasting and CRC". 2005-06-29. Retrieved 2007-10-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
29. "Digital Radio: State of the Industry - CRTC Opens Doors to Multiple Digital Radio Standards". Retrieved 2007-10-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
30. "Canada Says "OK" to HD Radio". 2007-01-02. Retrieved 2008-01-02. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
31. "IBOC Technology: An Assessment of Technical & Operational Issues in the Canadian FM Radio Environment" (PDF). 2007-05-27. Retrieved 2007-10-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
32. "First Report & Order (U.S. FCC)" (PDF). 2002-10-11. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
33. "Second Report & Order (U.S. FCC)" (PDF). 2007-05-31. Retrieved 2007-10-29. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
34. Pizzi, Skip (2007-09-01). "Subscription Radio Gets Real". Radio World. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
35. iBiquity Digital Corporation - HD Radio Products
36. Ford to Offer Factory-Installed HD Radio Technology on Ford, Lincoln and Mercury Vehicles in 2009
37. DICE Electronics

External links

• HD Radio official site
• iBiquity
• U.S. Federal Communications Commission IBOC Page

• Broadcast engineering
• Digital radio