HD Radio

The HD Radio Logo

The HD Radio Logo

HD Radio is a brand name of a method of in-band on-channel transmission of AM and FM radio stations. The HD Radio system is unique in that it allows stations to simulcast MP3-quality compressed digital audio and traditional analog audio, without changing to new frequency bands. "HD" originally stood for "Hybrid digital/analog" during its engineering development, but presently represents "Hybrid Digital" according to Diane Warren at the HD Digital Radio Alliance. [2] (Note that it is not "high definition" as is the case with HDTV.)

The technology was developed by iBiquity Digital Corporation. The Federal Communications Commission selected HD Radio (a hybrid system in which digital signals are sent along with the analog carrier) as the standard for AM and FM broadcasting in the United States. FM stations can offer multiple channels (called "Multicast" channels) on the same frequencies allocated to analog radio stations. iBiquity Digital claims that the system approaches CD quality sound and offers reduced interference and static. In March 2007, the FCC approved a nationwide rollout of HD radio technology creating widespread harmful interference especially in the AM broadcast bands.

As of 2007, more than 1200 stations are broadcasting with HD Radio technology and more than 550 offering Multicast channels. although there are very few AM stations using IBOC at this present time due to fear of consumer complaints of interference. Like traditional AM and FM stations, HD Radio programming is free at this present time, but NDS, a maker of digital media encryption technology, recently signed a deal with iBiquity to provide HD Radio with an encrypted content-delivery system that effectively institutes subscriptions capability on digital radio, so it may not be free for long. ( http://www.diymedia.net/archive/0407.htm ) Brand name (Sony, Cambridge Sound Works, JVC, etc.) 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.

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 Federal Communications Commission (FCC) in 2002, but the system was changed to the HDC codec in 2003 (based-upon MPEG-4 AAC). HD Radio-equipped stations must pay royalties each year to iBiquity, plus the costs paid by the manufacturers of the transmitters which are then passed along to the stations that buy them.

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. If in the future the FCC decides to discontinue analog broadcasts which is very much in doubt, then the HD Radio is designed to revert to a very-low-speed ~20 kbit/sec stream (equivalent to telephone quality). 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. Datacasting is also possible, and RDS-like metadata about the program and station are included in the standard.

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, consumers have shown little interest in HD Radios, with far fewer than 500,000 units sold in the U.S., Also the rejection of HD Radio by carmakers may be another serious obstacle to widespread adoption by consumers. HD radio has so far gone over like a lead balloon. [3]

AM

The AM hybrid mode offers two options which can carry approximately 40 or 60 kilobits per second of data for the main audio channel (achieving MP3-like quality), but the higher the bit rate, the more vulnerable the signal is to poor reception, so most AM-digital stations default to the more-robust 40kbit/s mode which features redundancy (same signal broadcast twice). If in the future the FCC decides to discontinue analog broadcast which is not in the plans at this time at all, the HD Radio would provide 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. [4]

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. Many audiophiles and non-local nighttime listeners have expressed concern this design harms reception of adjacent channels. [5] An MP3 sample of the interference: [6] (Note: The pure digital signal fits inside a standard 10 kHz channel (40kbit/s) or an extended 20 kHz channel (60kbit/s), at the discretion of the station manager.)

Most analog AM radios have electronic filters to remove all signals more than 5 kHz away from the center frequency, but some "wideband" receivers do not filter this way, making the encoded signal audible. Even on radios that do have such a filter, it is possible to hear the digital sidebands by tuning above or below the desired frequency by 10 kHz. Proposals for AM stereo have produced similar controversies. 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 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 broadcast, as they decided to do 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 also includes 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 (example: FM97-HD1, HD2, HD3) of varying audio quality (50, 25, 12, or 5 kbit/s are the values recommended by Ibiquity). National Public Radio in particular hopes to be able to carry several different streams through the transmitters of member stations, calling its proposed addition to the FM standard "Tomorrow Radio". The multiple distinct services are similar to the sub-channels found in ATSC-compliant Digital Television and typically called multicasting but actually more like multiplexing. Second and third channels, such as for weather, traffic, or a radio reading service, can be added this way, though it will reduce the audio quality of all channels on a station. Stations may eventually go all-digital, meaning they could no longer be heard on analog-only radio receivers, and thus allowing as many as three primary channels of full-power and four secondary channels of low-power (seven total). As defined by iBiquity, these channels would consist of two 98kbit/s FM-quality channels, four 25kbit/s sub-AM-quality channels, and one 5 kbit/s Talk channel.

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.

Bandwidth

Currently, FM stations in the United States and Canada are licensed to occupy approximately 200 kHz of RF spectrum, i.e., the FM band frequency allocations are 200 kHz apart. When a signal modulates the carrier, an infinite number of harmonically-related sidebands are created, thus the actual occupied bandwidth of the signal extends well past the highest modulating frequency (usually ± 100 kHz), because of the non-linear nature of frequency modulation. In order to prevent harmful interference to other stations, the carrier frequencies of stations within individual markets are seldom authorized to be closer than four channels apart, equal to 800 kHz. Occasional exceptions exist with spacing of three channels (600 kHz). In addition, there are constraints on occupied bandwidth as such. Transmitted RF energy in the sidebands more than 120 kHz from the center frequency is required to be significantly attenuated. In the modulation baseband, FM stations have a bandwidth of about 100 kHz, only 15 kHz of which is used by analog monophonic) audio. Analog stereo uses 53 kHz of baseband 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, or as a transmitter-studio link for in-house telemetry.

While the various baseband signals all contribute in a complex manner to the total occupied bandwidth (and modulation level) of the FM signal, it is important to consider two factors. First, the modulating signal will generate a principal RF component at the fundamental sideband frequency, e.g., a 67 kHz subcarrier will generate RF components at ± 67 kHz from the FM carrier. Second, any filtering of the modulated signal, or bandwidth limitation in the transmission system, causes a certain amount of distortion in the received signal, due to the formation of intermodulation components from the various modulating signals.

In regular hybrid mode, an HD Radio station has its full ± 100 kHz of RF bandwidth, and adds its digital signals into part of the upper and lower adjacent RF channels beyond that, using about 1% of the main FM power level. 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. This will require new receiving equipment for subscribers, however. The current analog stereo subcarrier would, in theory, eventually be dropped to make more room for digital transmission, and eventually stations could elect to drop the analog baseband (monophonic 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.

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. 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. Some interference of this type is already permitted by FCC assignment rules, and the amount caused by HD Radio is expected to be accepted as well. A distinct possibility exists of interference between HD stations in neighboring markets, which may be assigned frequencies only one or two channels apart.

• IBOC Spectrum (subcarriers): markers are on channel center frequencies
• 
  Spectrum of FM broadcast station without HD Radio
• 
  Spectrum of FM broadcast station with HD Radio

Comparison to EU's Digital Radio Standards

FM-HD Radio versus DAB

Most of the nations of the European Union have implemented Digital Audio Broadcasting (DAB), with compatible radios hitting shelves in 1999. In the United States, both analog radio and HD Radio are broadcast on different frequencies via FM, each 100 kilohertz wide, and the radio has to be tuned into each frequency. In contrast DAB uses spread spectrum technology to broadcast a single station that is approximately 1500 kilohertz in width (~1100 kilobits per second). That station is then subdivided into multiple digital streams of between 6 and 8 channels. In order to implement DAB, it was necessary for the ETSI to set-aside new bandwidth, whereas HD Radio shares its digital broadcast with the traditional analog FM band.

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 due to the bit rate levels used on DAB being too low. For example, on 6 July 2006 the BBC reduced the bit-rate of transmission of Radio 3 from 192 kbps to 160 kbps. The resulting degradation of audio quality prompted a number of complaints to the Corporation. For comparison, the HD Radio standard allows up to 300 kbps for each FM station.

Other issues with DAB include "downgrading" stations from stereo to monaural, in order to squeeze even more channels into the limited 1100 kilobit/second bandwidth, smaller coverage of markets as compared to analog FM, radios that are overly expensive, and poor reception inside vehicles or buildings. HD Radio shares some of these same flaws (see criticisms below).

AM

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 radio and HD Radio, in that each station is broadcast on different frequencies via AM, each 10 kilohertz wide, and the radio needs to be tuned into each frequency. The two standards also share the same modulation scheme (COFDM), and like HD Radio, DRM allows broadcasters multiple options:

• Hybrid mode (analog and digital) - 5 for AM, 5 for DRM at 10 kbits/sec - (HD Radio is 40-60)
• Single-wide mode (digital only) - 10 kilohertz for DRM at 20 kbits/sec - (HD Radio is 40)
• Double-wide mode (digital only) - 20 kilohertz for DRM at 40 kbits/sec - (HD Radio is 60)

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, and poor reception inside vehicles or buildings.

Receivers

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

Automotive

Receivers are becoming less expensive, starting at around US$125. 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.

• Alpine Electronics TUA-T500HD tuner module for Alpine receivers only
• DICE Electronics HD DICE universal add-on tuner for factory radio integration, currently the only one available
• Directed Electronics DMHD-1000 universal add-on tuner, requires an external screen
• JVC KD-HDR1 receiver for JVC receivers only
• Kenwood KTC-HDR1 add-on tuner for Kenwood receivers only
• Sony XT-100HD add-on tuner for Sony receivers only
• Visteon HD Jump dockable tuner universal add-on tuner, requires an external screen
• Visteon HD Zoom add-on tuner kit universal add-on tuner, requires an external screen

Home/Office and Professional

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

• Audio Design Associates Tune Suite Quadritune HD Radio/XM/Sirius Tuner
• Audio Design Associates Duo Tuner HD Radio/XM/Sirius Tuner
• Audio Design Associates TSS-1 HD Radio Module (for Tune Suite and Duo Tuner)
• Audio Design Associates HD-Pro Dual HD Radio Tuner
• Boston Acoustics Receptor HD table top radio
• Cambridge Soundworks Radio 820HD Tabletop radio
• Day Sequerra M2.0X HD Radio Modulation Monitor
• Day Sequerra M2.2X HD Radio Modulation Monitor
• Day Sequerra M3 HD Radio Multi-Monitor
• Day Sequerra M4.0X HD Radio Tuner
• Day Sequerra M4.2X HD Radio Tuner
• Day Sequerra M4C HD Radio Tuner
• Day Sequerra MAM HD Radio Market Area Monitor
• Directed Electronics DHHD-1000 tabletop radio.
• Onkyo TX-NR905 surroundreceiver
• Polk Audio I-Sonic™ Entertainment System Table top radio.
• Polk Audio Designs Executive HDX3] Shelf system.
• Radiosophy HD100 tabletop radio.
• Radio Shack Accurian 12-1686 table top radio
• Sangean HDR-1 tabletop radio
• Sangean HDT-1 and HDT-1X component tuners
• Sony XDR-S3HD tabletop radio
• Viesteon HD Jump Portable dockable receiver
• Yamaha RX-V6400 A/V receiver

Portable

Portable HD Radio receivers are currently unavailable because the currently available chipsets draw a significant amount of power, making portable models impractical. As new lower-power chipsets are introduced, portable receivers will be built, probably by the end of 2007.

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 although the majority of these companies' stations do not use IBOC (Hybrid Digital), has urged its HD 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, although this has not happened to any great extent as of this writing

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.

Criticisms

HD Radio tuners have been noted to be very insensitive, making reception very problematic. In hybrid mode, the HD Radio signal is 1/100th the power of a station's analog power. For this reason, the HD Radio signal will sometimes drop out and the receiver will revert to analog mode. This can be problematic in fringe areas, as 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 standard with virtually all automobiles, HD Radio requires consumers to purchase a new radio costing more than $100.

External links

• HD Radio official site
• iBiquity
• WOR Transmitter Tour, containing information on an early IBOC installation
• RadioSherpa online electronic program guide for HD radio stations
• HD Radio Alliance HD Radio Marketing site
• Marketing challenges for HD radio
• Open Geek: HD Radio clips Audio samples of actual HD Radio broadcasts
• HD Radio Reception from Rochester, N.Y. Audio samples from Rochester, NY HD Radio stations