Last issue, I told you about Digital TV and the DTV transition. This month, I'm going to talk about another kind of HD: HD Radio, and how it applies to you.
The actual underlying technology in broadcast radio really hasn't changed much in the last 50 years or so. As a result, the system is quite out of date, and is literally the last medium to go digital.
A (super brief) history of radio:
AM radio, the first broadcast radio band became standardized in the 1920s. The band runs from 530 KHZ - 1710 KHZ (1.71 MHZ). At those frequencies signals travel along the earth's surface (rather than line of sight).
After years of experimentation and standardization (which took place before and during WWII), the FCC allocated the 88-108 MHZ band for FM broadcasts. While FM offered much higher quality audio than AM, it was still mono. In the early to mid 60s, the FCC reviewed and selected a standard FM Stereo system, out of 14 competitors.
Evolution of radio technology:
Failed FM systems
FM has always been a prime candidate for tweaking and improvements. Some lasted, some didn't.
In the late 60s and early 70s, a number of different systems arose to broadcast the quadraphonic sound. These quickly died out due to lack of interest. In the late 70s, the Dolby corporation released Dolby FM, a modified version the noise reduction scheme found on cassette tapes, which would allow for better FM with lower noise. It, too died. FMX, another radio noise reduction scheme came along in the early 80s. It also hit the fan.
Successful FM improvements
One lasting "improvement" was the use of subcarriers, low power signals slightly lower or higher in frequency than the main signal, which carried content such as background music services, reading for the blind, etc... In the early 1990s, stations began adopting the Radio Data System, which allowed stations to broadcast station, artist and track info to equipped receivers (found in many recent cars). Broadcasting RDS is actually fairly common in larger markets today.
In the 1980s, FM radio finally became the dominant broadcast band. Work was done to improve AM radio. The improvement - AM Stereo. In the mid 1970s, the FCC started testing competing AM Stereo systems, and announced the winner in 1980: the Magnavox system. After lawsuits, accusations of bribery and general public outrage, the FCC decided to let stations use whatever system they wanted. Mayhem ensued. At first, stations chose any of the four systems, and so did receivers, confusing consumers to no end. Eventually, the industry formed a standard called AMAX, which maximized sound quality, and ensured that all AMAX receivers could decode all four standards. Eventually, Motorola's standard (C-QuAM) came out ahead, and the FCC adopted it as the official standard in 1993. In America, and most other non-third world nations, this was the end of it (AM Stereo is still in heavy use in some countries).
The dawn of HD Radio
The audio and video realm is almost completely digital now. In fact, the only major realm that isn't digital is radio. Many European nations have been broadcasting digital radio (the Digital Audio Broadcast [DAB] standard) since 1999.
In 2002, the FCC selected the iBiquity corporation's HD Radio standard for digital AM and FM broadcasts. There are two basic broadcast modes for HD Radio: hybrid (digital and analog) or all digital. Currently, all stations broadcasting HD Radio are using a hybrid mode. Currently, the system is broadcast on subcarriers at 1/100th the power of the analog counterpart. While the FCC hasn't given out information about all digital broadcasts, it's estimated that a digital broadcast 1/10th the power of the analog one will reach farther than the analog broadcast.
In Hybrid mode on FM, stations can broadcast one "CD Quality" station, or two "MP3 Quality" stations. It's even possible to add a third channel, capable of lower quality stereo, or high quality mono channel. In addition, the system is capable of broadcasting artist/album/song information, station call letters, the station's name, and the current time. In all digital mode, stations can do 6-7 stereo streams, and possibly even surround sound!
AM stations can broadcast HD Radio as well. The digital channel is capable of FM quality stereo sound, and the aforementioned text data. In all digital mode, AM stations could broadcast higher quality audio, or possibly even two lower quality channels.
Currently, HD Radio broadcasts can really only be received where you have a strong analog signal. In certain situations, you might have to improve reception by getting a better indoor, or outdoor antenna. However, the digital signals are a lot more resistant to multipath reception than analog. In fact, some users can get a solid HD lock where the analog sounds terrible. In the future, when stations go all digital, they'll be able to reach farther than the old analog signal.
From 2002-2005, there were only a few stations testing the technology, and the number of receiver models could be counted on one hand. In the time since, things have really taken off.
At the time of writing, 1564 stations broadcast HD Radio, and there are 2,354 channels on those stations. In fact, most stations in large markets are broadcasting in HD Radio! If you'd like to see what stations are available in you area, check out the listings at hdradio.com. As you can see, many stations are broadcasting other "HD-2" and "HD-3" channels. The "HD-1" channels are the same as the analog station, while the HD-2 and 3 channels broadcast.
Basic lesson in radios: From the introduction of radio until the late 50s, most equipment used vacuum tubes and various components. From the late 50s until the 80s, most radios used transistors and various components. From the 80's until present, most radios had digital readout, used chips instead of individual components, but were still analog on the audio side. HD Radio is helping push another technological advance: Digital Signal Processing (DSP) based radios. In a nutshell, DSP receivers process the signal entirely in the digital domain, and are much more sensitive (able to pull in weak signals) and selective (able to reject adjacent stations) than ordinary radios.
While this is a huge technological advance, tuners are rather hard to come by. Their most prevalent in the car radio market. Some $70 aftermarket radios (such as those made by Dual) are equipped with HD Radio!. Table top radios, receivers with HD and component tuners are also available, but harder to come by.
HD Radio looks like it's here to stay. If your in the market for a new car radio, it's certainly something to consider, especially with the low cost of equipped models. Right now, the technology is in the early adopter stage, but should become mainstream in five years or so. For more information, check out hdradio.com for available radios and stations in your area.