The average listener doesn’t realize it, but the worldwide AM/FM radio infrastructure has a great deal more to offer than what the standard home receiver or car radio can capture. Finding what’s really out there takes digital radio. In coming months, AM/FM radio listeners who would like to enjoy higher quality sound will not have to sign up for satellite radio subscriptions or install considerably more expensive radio receivers to relive the sweet sounds of last week’s Nora Jones concert on the drive to work.
Analog vs. digital radio
Today, with analog radio broadcast, radio reception can suffer for a variety of reasons. Adjacent radio signals often interfere as signals bounce off buildings, mountains or other obstructions. The radio receives more static and the station fades as the listener gets further away from the radio tower. All of this results in additional audio noise and the sound fidelity being less than optimum. Applying some of the digital signal processing used in stereo systems can easily improve the quality of radio reception.
According to a June 2002 report from analyst firm Allied Business Intelligence, sales of digital radios will jump nearly 50-fold to 33 million units by 2007. The term “digital radio” can have multiple meanings. It can mean how radio waves are transmitted and received as well as how a radio receiver tunes and separates the constant AM or FM carrier signals from the variable audio signals. With digital radio, the benefits to listeners are numerous: less static, fading, pops and hisses; automatic tuning, so adjacent stations won’t interfere with each other; extended listening range from existing signals; and overall improved audio clarity and volume. The bottom line is that listeners can hear more stations, whether at home or on the road, tune to more remote stations with greater ease and enjoy higher quality sound.
One type of digital radio available commercially in the United States is satellite radio. Subscriber-based, this service is enabled by orbiting satellites that broadcast signals from more than 22,000 miles above the earth. Similar to satellite TV, listeners cannot pick up local stations, but do have access to hundreds of channels offering a variety of music genres, transmitting high quality audio and data, such as song titles and artists. Because competing satellite broadcasts are not compatible, once listeners select a satellite radio provider, they cannot switch between satellite systems based on cost or services. Further, if a listener chooses a satellite broadcast provider that fails economically, what is left is the equivalent of a beta cassette recorder.
Digital radio employs two land-based methods, both of which require radio receivers to be adapted in order to receive digital audio signals. HD (high definition) Radio (formerly IBOC, for in-bound out-channel) technology, developed by iBiquity Development Corp., uses a new modulation scheme requiring broadcasters to upgrade their broadcasting equipment. It works by wrapping digital signals around the old analog signals.
Radio stations can broadcast both digital and analog signals, but will have to upgrade their transmitting equipment for the digital broadcasts, a very expensive proposition that can cost stations between $30,000 and $200,000, depending on the condition of their current equipment. HD Radio is not subscriber-based, but listeners will have to buy a receiver that could cost $100 more than a standard AM/FM radio. Because of “growing concerns over the audio quality of iBiquity’s low bit-rate codec,” the National Radio Systems Committee (NRSC) digital audio broadcasting subcommittee recently temporarily suspended its standard-setting process around IBOC. So, consumers and broadcasters who choose HD Radio may find themselves at a technological dead end.
A different approach to digital radio
A newer land-based approach to digital radio, Motorola’s Symphony? digital radio platform, was introduced in October 2002. It uses existing AM and FM signals and employs digital signal processing and software technology in radio receivers to tune in the signal and eliminate interference. The technology may be used anywhere in the radio spectrum and is being applied initially in radio receivers targeting analog AM and FM signals. Impressed by the superior audio quality in tests against high-end analog sound systems, consumer electronics manufacturers plan to introduce radios in 2003 based on the Symphony digital radio technology.
Because it is software based, upgrading and customizing the radio becomes similar to upgrading software on your PC. Radios can be customized for different regions of the world and for different consumer tastes – it is even possible for radios to be upgraded in the field by listeners.
“In our quest to bring music lovers an ever-improved listening experience, we are always looking for new technologies that will help us advance sound quality and signal reception performance,” said Hyundai Autonet President J. J. Yoon. “Symphony digital radio is truly a breakthrough technology for the radio industry much as the CD was for the recording industry.”
Symphony digital radio’s chipset approach to digital radios combines a 24-bit DSP core popular with consumer audio applications with an RF (radio frequency) front-end and IF (intermediate frequency) analog interface. The technology allows consumers to receive much more from all the existing AM/FM broadcast signals without paying a monthly subscription fee or requiring broadcasters to invest in new transmission equipment.
Here are some highlights of the newest technology to enable digital radio:
The variable IF filter algorithm automatically and dynamically adjusts itself to both 100KHz and 200KHz band channel spacing allowing it to react to any changes in atmospheric conditions or radio location.
The channel effects equalizer allows travelers to “hold on” to a clear signal longer. This gives a better chance of hearing the whole ballgame rather than frantically scanning through the radio band for a new station just as the teams go to the ninth inning.
Minimized multipath distortion allows listeners to hear a favorite station from further away. With traditional analog radios, the deteriorated sound quality would already have resulted in a station change.
The FM demodulator algorithm separates the FM signal from the carrier, provides exceptional range extension and improved Signal-to-Noise Ratio (SNR) under weak signal conditions. In other words, it enables a radio receiver to pick up weaker signals from a greater distance and still provide sparkling clear reception.
The software architecture enables excellent stereo separation, often greater than 40dB. This allows for audio processing and radio tuning simultaneously on a single processor/software thread and enables the handling of dual audio streams. By using a software approach to digital radio implementation, manufacturers can expect to reach exceptional levels of digital IF radio integration in a smaller and far more flexible form factor.
Motorola’s Symphony Digital Radio platform
According to its May 2002 report, the technology forecasting firm In-Stat/MDR expects to see one in every two radios sold in America equipped with a digital decoder by 2006. From the radio manufacturers’ perspective, Symphony digital radio enables advanced capabilities for about the same cost-per-unit as current analog radio receivers. However, consumer can expect to enjoy a vast improvement in radio audio quality without shouldering any significant additional cost.
For Christmas 2003 a new, unheard world of audio entertainment is expected to reach listeners in the form of aftermarket AM/FM automotive radios. Symphony digital radios as original equipment in cars should appear in 2004.