OTHER TECH

Digital Radio Comes Down to Earth Page 5

HD Radio on the Road
Since most people do their radio listening in cars, and since HD Radio is said to be immune to multipath interference-that annoying "picket fence" phenomenon so familiar to drivers listening to FM radio-we were eager to go for a spin with a digital receiver. But because no HD Radio receivers were yet on the market, iBiquity set us up with a test van that would let us experience both AM and FM digital radio in real-world conditions.

I have no idea what head unit was installed in the van's dash. But it didn't much matter because my attention was focused on the two racks behind the rear seat (don't worry, I wasn't driving!). They were filled with gear like a headphone amplifier, audio switcher, spectrum analyzer, and a couple of head units, including a Visteon HD Radio prototype.

Anxious to hear what HD Radio sounded like, I quickly tuned to WOR-AM, New York's first digital station. Talk radio might not be the ideal format for judging the sound quality of HD Radio, but a few seconds after the display verified that it had switched to digital reception, I was able to discern a slight drop in background noise, even on WOR's powerful, 50,000-watt signal. There was also a slight overall level drop, which we were told would be fixed shortly with a change in equipment at the station.

The jingles on WOR's many commercials ultimately provided a better sound-quality test. It's hard to say that digital AM sounds as good as analog FM, as iBiquity claims, but the digital signal did have noticeably better sound, with a more open top end and a complete lack of static.

What we really wanted to hear, though, was what digital could do for FM, so we punched in the New Jersey rock station WDHA. The southern rock anthem "Sweet Home Alabama" was playing, and when the Visteon receiver switched from analog to digital, I heard a distinct improvement in the treble and left-right stereo separation.

Because of the time it takes to lock in a digital signal, HD Radio receivers have a 4-second data buffer and are designed to tune the analog signal first. They will also drop back to analog if the digital signal is lost, which helps to eliminate dropouts. To keep everything in sync, HD Radio stations are supposed to delay their analog broadcasts by 4 seconds relative to the digital stream. But WDHA wasn't doing this-it has yet to announce its digital signal publicly-which allowed us to do direct A/B comparisons of 4-second musical snippets. It also made it obvious when the digital signal fell back to analog-which wasn't often. In fact, the digital signal's coverage area seemed to be about the same as the station's analog stereo coverage area. And as a drive through downtown Patterson, NJ, showed, the digital signal was immune to multipath. As far as we could tell from our short road test, HD Radio technology lives up to its "Pure Digital. Clear Radio" tag line.

- Brian C. Fenton

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