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HD Radio

HD Radio

It’s the most significant advancement in radio broadcasting since the introduction of FM stereo more than 50 years ago. HD Radio technology enables AM and FM radio stations to broadcast their programs digitally – a tremendous technological leap from the analog broadcasts of the past.

Since HD Radio is a free broadcast, all you have to do is get a new HD Radio receiver for your home or car.

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 MP3-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". The name "Hybrid Digital" is derived from the latter operational mode, and not high definition as some erroneously believe.

As of 2007, more than 1200 AM and FM stations are broadcasting with HD Radio technology, with more than 550 FM stations offering Multicast channels, thus doubling or tripling the number of programs available to listeners. Most of the stations that have adopted the technology are FM, while AM stations have been slower to upgrade. As with traditional AM, FM and TV broadcasting, HD Radio programming is free and supported by commercial advertising. 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.

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 royalties each year to iBiquity, plus costs paid by the manufacturers of HD transmitters and passed along to the stations that buy them.

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 (equivalent to telephone-quality audio). Datacasting is also possible, and RDS-like metadata providing song titles or artist information are included in the standard.

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.

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 kHz, 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. 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 electronic filters to remove all signals outside the 10 kHz channel, but some "wideband" receivers do not filter this way, making the encoded signal audible. Even on radios that include the 10 kHz filter, it is possible to hear the digital sidebands by tuning above or below the desired frequency. Proposals for AM stereo have produced similar controversies. iBiquity's standard is incompatible with C-QUAM AM stereo broadcasts.


HD Radio Transmitter
Spectrum of FM broadcast station without HD Radio
Spectrum of FM broadcast station with HD RadioThe FM hybrid digital/analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of data depending upon the Station Manager's power budget and/or desired range of signal (achieving MP3-like quality). 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, thus enabling extra features like surround sound or near-CD-quality audio (CD=1400+ kbit/s). 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. [16] 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.

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. 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 for a very long time, if ever.

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.

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 nations have implemented Digital Audio Broadcasting (DAB), with compatible radios hitting shelves in 1999. In the United States, both analog FM radio and HD Radio stations are broadcast via a channel 200 kilohertz wide, and the radio is hand-tuned to each individual station's location on the dial. In contrast DAB uses spread spectrum technology to broadcast 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 HD Radio shares its digital broadcast with the traditional analog FM band (In-Band On-Channel).

In the UK, Denmark, Norway and Switzerland, which are the leading countries with regard to implementing DAB, the vast majority of stereo radio stations on DAB have a lower sound-quality than FM prompting a number of complaints [18][19]. The typical bandwidth for DAB programs is only 128 kbit/s using the older, less-robust MPEG-1 MP2 standard which requires at least double that rate to be considered near-CD quality. For comparison, the HD Radio standard assigns up to 300 kbps for each individual FM station, using a more-advanced MPEG-4 HE-AAC-derived standard that can achieve near-CD quality as low as 64 kbit/s.

Other issues with DAB include "downgrading" stations from stereo to monaural, in order to squeeze even more channels into the limited 1000 kbit/s bandwidth, smaller coverage of markets as compared to analog FM, radios that are overly expensive, poor reception inside vehicles or buildings, and a general lack of interest in DAB (only 3 million units sold (UK)). HD Radio shares some of these same flaws (see criticisms below).

AM-HD Radio versus DRM
The European Union nations are in the process of rolling-out Digital Radio Mondiale (DRM), with compatible radios hitting shelves in late 2006. DRM is very similar to traditional analog AM radio and 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), and like HD Radio, DRM allows broadcasters multiple options:

Hybrid mode (digital/analog) - 10 kHz AM + 5 kHz DRM at ~10 kbit/s
Single-wide mode (digital only) - 10 kHz DRM at ~25 kbit/s ----- (HD Radio is 20-40 kbit/s)
Double-wide mode (digital only) - 20 kHz DRM at ~55 kbit/s ----- (HD Radio 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: Lower sound-quality than FM, shorter broadcast distance as compared to analog AM, radios that are overly expensive, poor reception inside vehicles or buildings, and interference with adjacent channels (15 kHz hybrid mode does not fit in the 10 kHz channel).

There is a general disinterest 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.

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. For this reason, 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. In addition it has been noted that the analog section displays poor reception capabilities compared to older non-digital models.

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. HD Radio has been officially adopted only by the US and Brazil. iBiquity has stated in PR articles that countries evaluating HD Radio include Canada, France, Mexico, New Zealand, the Philippines, Switzerland, and Thailand. However as of mid-2007, Canada and Switzerland have officially selected, or are 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.

HD Radio has been criticized for being incompatible with the standards selected by most other countries; hence overseas travel with an HD Radio, or the sale of radios to or from countries that don't use HD Radio is not possible. Manufacturers presently must design and build separate radios for the U.S. market. For broadcasting on frequencies below VHF (including Shortwave and AM/Medium Wave), most countries (and the standards organizations ITU, IEC, and ETSI) have adopted the Digital Radio Mondiale system, abbreviated "DRM" (not related to Digital Rights Management). For VHF and higher frequencies, a majority of countries have adopted or are evaluating the Digital Audio Broadcasting, abbreviated "DAB" system (see "Regional implementations of DAB" in Digital Audio Broadcasting).

The U.S. FCC selected HD Radio as the official digital radio system in 2002, and without provision for compatibility with DAB (ratified by the ITU-R standardization body in 1994) and DRM (ITU ratified April 2001). Thus, although an analog radio from one continent can be taken to another and it will work to some degree, the differences between HD Radio and DAB/DRM make listening to the other system impossible.

Unlike subscription-based satellite radio, the content of HD Radio stations is subject to FCC regulation.

Unlike regular car radios, which come fitted as standard equipment with virtually all automobiles, HD Radio requires consumers to purchase a new radio costing more than $100.

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 multicast (HD2, HD3, etc.) signals. 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 97.1's HD2 channel. It is common practice to broadcast a former FM station's format on its HD2 channel, such as WPGB (104.7 FM) in Pittsburgh, which carries the smooth jazz format on its HD2 band. Said station was once known as WJJJ.

Other recent additions include introduction of airstaff on HD2 stations, like KDWB's Party Zone channel in Minneapolis-St. 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.

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