Digital Audio: Amps, Preamps & Receivers

Sept. 27, 2004
The digital revolution bypassed radio until the late-2001 launch of Satellite Digital Audio Radio (SDAR) service. Today, two satellite-radio broadcasters — Sirius Satellite Radio and XM Satellite Radio — compete to beam more than a hundred channels each of coast-to-coast music, entertainment, and information programming to compatible car radios, home radios, and boomboxes.The broadcast services expose radio listeners to a diversity of music and information programming, and they deliver the same programs nationwide without the multi-path distortion and static that afflict terrestrial analog radio stations. As a further incentive to subscribe, both services make select songs available in surround sound, and their selection of surround sound music will continue to grow.The stations have proven so popular that the number of satellite-radio subscriptions broke the 1 million mark in late 2003, only a year and 10 months after the service launched. The adoption pace was second only to that of DVD players and far exceeded the speed with which consumers bought the first million radios, TVs, or VCRs, according to XM. By the end of 2004, the services forecast a combined subscriber base of about 3.9 million.Meanwhile, terrestrial analog AM and FM stations have been installing equipment to launch commercial digital service. Hundreds of AM and FM stations are making the conversion to digital broadcasting, yet continue to deliver analog signals to consumers’ existing analog radios.In late 2002, the Federal Communications Commission (FCC) gave AM and FM stations interim authority to transmit digital programs using the HD Radio standard developed by iBiquity Digital. It’s an In-Band On-Channel (IBOC) standard that lets existing AM and FM stations use their existing transmitters, antennas and dial positions to deliver high-quality interference-free digital audio — and without the monthly subscription costs required by satellite-radio broadcasters.By early 2004, about 290 stations in 79 markets in 37 states had licensed the technology. They included stations in the top 10 markets and 39 of the top 50 markets. The majority were expected to be broadcasting digital signals by mid-2004. By the end of 2004, technology developer iBiquity expected about 600 to 650 stations to be broadcasting in digital to 80 percent of the U.S. population.What consumers will get out of these broadcasts will exceed the promises of iBiquity’s original technology. The original codec promised near-CD-quality sound from digital FM stations. Digital AM stations were supposed to deliver sound quality close to what analog FM stations deliver. The new codec, in contrast, promises digital FM stations that sound “statistically indistinguishable” from CDs. AM stations will sound as good or better than today’s analog FM stations, iBiquity said.Like before, digital broadcasting will minimize adjacent-channel interference and virtually eliminate multipath, noise and interference that reveal itself as static, hiss, popping sounds and fading. Like their satellite counterparts, terrestrial digital stations will deliver program information such as song titles and other data.Because it’s an IBOC technology, HD radio makes it possible for digital stations to simultaneously serve analog-radio users. IBOC technology lets broadcasters deliver simultaneous analog and digital versions of the same program on their assigned frequencies.The dual analog-digital approach serves another purpose: a station’s analog signal will back up a dropped digital signal to ensure uninterrupted service. The dual approach is needed because, with digital broadcasting, there’s no such thing as receiving a degraded digital signal. You get a pristine signal or no signal at all. That’s called the cliff effect. To prevent cliff-effect digital dropouts, a digital radio gradually switches over to analog reception during digital-dropout periods. Digital dropouts aren’t expected to happen often, however, because digital stations broadcast a second digital signal as a backup.iBiquity’s technology has been endorsed by 15 of the top 20 U.S. radio broadcast companies and by the National Radio Systems Committee (NRSC), which is jointly sponsored by the Consumer Electronics Association (CEA) and the National Association of Broadcasters (NAB). The NRSC based its endorsement on the results of field, lab and listening tests conducted by independent test labs and monitored by NRSC representatives.From the tests, the NRSC concluded that the digital FM technology delivers “greatly reduced impact of multipath interference (for mobile, portable and fixed receivers alike), superior resistance to co-channel and adjacent-channel interference, support for enhanced data services, [and] improved audio quality.”By late 2004, select automakers are expected to begin offering HD radio in a limited selection of 2005-model-year vehicles. iBiquity expects automaker availability to take off in calendar 2005. On the home front, several home audio suppliers are expected to offer digital AM/FM tuners by the end of 2004.Sound quality and song-title display aren’t the technology’s only advantages. HD radio has the capability to deliver fee-based information services and audio program management (APM), which time-shifts a program much like a PVR (personal video recorder) for a TV set. Digital radio also makes it possible for an FM radio station to deliver two separate programs simultaneously on its assigned frequency and broadcast in surround sound. AM stations could deliver surround sound, but they lack the bandwidth of FM stations to deliver two programs simultaneously.The separate audio program feature is called Tomorrow Radio by its backers, which include National Public Radio (NPR). It works like this: instead of an FM station broadcasting a 96 kilobits-per-second (kbps) CD-quality signal, the station would broadcast a high-quality 64 kbps program and a supplementary 32 kbps program. Proponents describe the 32 kbps program as satisfactory for a mixed speech and music service, and it would still be interference-free.To provide surround sound, iBiquity is endorsing the installation of Circle Surround II encoders at AM and FM stations. Stations would use Circle Surround encoders to transmit stereo-compatible 5.1-channel music from multi-channel recordings, including multi-channel music played from DVD-Audio discs and Super Audio CDs. Home and car audio systems equipped with Circle Surround II decoders would hear the music the way it was mixed. Systems using other surround decoders would also deliver a surround-sound experience, but not necessarily in the way that the music was originally mixed.Circle Surround II encoders were available for sale to radio stations in early 2004, when decoders were available in select home receivers. Car audio systems using the technology were under development in early 2004, when decoders were available in select home receivers. Car audio systems using the technology were under development in early 2004.Finally, iBiquity Digital’s HD technology supports “backward and forward” compatibility, allowing radio receivers and other consumer electronics to receive traditional analog broadcasts from stations that have yet to convert and digital broadcasts from stations that have converted. Current analog radios will continue to receive the analog portion of the IBOC-based broadcast, enabling a smooth transition to a digital world.In fact, specific features have been designed into iBiquity Digital’s IBOC technology to improve the existing analog reception during the “hybrid mode.” As the market reaches maturity, broadcasters are expected to transition out of analog broadcasts and offer “all-digital mode” in much the same way that television stations did with black-and-white programming.THIS ARTICLE IS DERIVED FROM “DIGITAL AMERICA 2004BY THE CONSUMER ELECTRONICS ASSOCIATION (CEA). GARY WARZIN OF AUDIOPHILE SYSTEMS, LTD. IS CHAIR OF THE CEA AUDIO DIVISION WHOSE MEMBERS INCLUDE REPRESENTATIVES FROM SONY, DENON, POLK AUDIO, DTS, YAMAHA, PIONEER, THIEL AUDIO, SHERWOOD, RUSSOUND, JVC, KLIPSCH, CONRAD-JOHNSON DESIGN, SHARP, GENELEC, PARASOUND, HARMAN, AND ATLANTIC TECHNOLOGY. CINDY LOFFLER STEVENS IS CEA DIRECTOR OF PUBLICATIONS.

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