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Time for DRM trials in the US?

Can all-digital band rescue AM radio?

Digital radio broadcasts were once floated by supporters as a way to "save" traditional radio from competing technologies such as iPods and the like. Whether radio needs saving - and whether technology rather than programming can save it - is up for debate.

Regardless, we now have digital radio.

You may not have heard it, as it currently supplements traditional analog broadcasts using a technology known as "in-band, on-channel" transmission. Essentially, the digital information is sent next to the regular analog broadcast. A regular radio still plays the analog signal, while a special radio can decode the digital signal. The system in the United States is called HD Radio.

(The HD in HD Radio doesn't stand for anything, by the way - it's just marketing, an attempt to latch onto the coattails of high-definition television's improved image.)

The way the current system works on an HD Radio tuner is interesting. Because it takes some time for the digital stream to be decoded, the radio first picks up analog, then within a few seconds shifts to HD. When done right, on FM the sound expands a bit and allows extra channels of programming. On AM, the sound suddenly cleans up and - compared with the typical AM radio - a better sounding signal comes out of the speakers.

HD Radio was supposed to be the savior of AM radio, which now reaches only about 30 percent of the listening audience nationwide. But it didn't work out that way. While there are some HD stations on the AM band in Los Angeles - KFI (640 AM), KBRT (740 AM), KFWB (980 AM), KNX (1070 AM) and KDIS (1110 AM) - the number overall in the United States is relatively small.
The problem, besides system costs, is interference.

HD Radio as it currently is implemented uses far more of the station's assigned channel, and with greater intensity, than what is used by straight analog. So the HD signal interferes with adjacent stations, causing that buzz you hear when you tune away from HD stations.

The required reduction of digital signal strength, combined with the interference, plus AM's technical limitations make HD reception spotty on all but the strongest stations ... such as KFI, KBRT, et al.

But HD Radio wasn't meant to be used in hybrid mode forever. Yes, having analog and digital allows current radios to still work. But there is an all-digital mode that would bring the signal back toward the center of the channel, reducing interference and allowing AM radio to thrive. Or so they say - no one really knows because it hasn't been tested in the real world.

That's where the National Association of Broadcasters steps in. A committee in the trade group, which is made up of member stations from across the United States, proposes to test all-digital broadcasts on the AM band. And the Beasley Broadcast Group - ironically, a company that tried HD on AM and turned it off - has offered one of its stations for use in the experiment.

The hope is that a full-digital AM band would actually reduce interference, extend the reach of digital broadcasts, and make AM popular once again. At least long-term. Before that can happen completely, almost every radio in the United States would have to be replaced, just as televisions were during their digital transition a few years ago.

That makes testing difficult, of course. AM may not be the dominant band, but taking a station essentially off the air for a period of time for testing is expensive. So I am not sure many station owners will match the offer of Beasley.

It is an interesting thought, though. And it opens up the idea of testing another digital system from Europe, called Digital Radio Mondiale, or DRM. I don't know the technical differences, but there are some supporters of DRM who feel that the all-digital DRM system would work better for AM than even the all-digital mode of HD. I have heard recordings of long-distance DRM broadcasts and I must admit they sound amazing.

One thing is certain: AM station owners need to decide once and for all what they want to do. Having only some stations using HD has hurt the band overall, and AM cannot stand more hurt.

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