OTHER TECH

(Homepage illustration by Dan Vasconcellos) You've been on a long drive, but you're now close enough to home to receive your favorite hometown station, right on time for the local news and then some music. A couple of miles after you tune it in, the sound suddenly blossoms, and the radio's display starts showing you what's playing and who's performing it. Welcome to HD Radio, digital radio piggybacked onto existing analog AM and FM signals-no satellites, no subscriptions.

New and ImprovedAnd about time, say radio broadcasters. In every area of audio but theirs, digital dominates. Our audio entertainment comes from CDs, DVDs, downloaded music files, and subscription satellite radio services. Only AM and FM radio are unswervingly analog-for now. Broadcasters have wanted to join the digital parade since CD's early days, but only if they could hold onto their existing investments and audiences.

With HD Radio, they can broadcast digital and analog together. About a dozen stations should be doing it by the time you read this, with several dozen coming on board by mid-year. Receivers for mobile and possibly home use should be out at the same time, with a few more coming this summer and fall, and more next year. Whether you get a digital tuner or not, you'll still tune into those local stations broadcasting in both digital and analog the way you always have, and you'll hear the same programs-but you'll get clearer sound and possibly additional information if you use an HD Radio receiver.

The extra clarity comes from wider frequency response and better radio reception, says iBiquity, the company that developed the system. On FM, HD Radio is immune to multipath distortion, "picket fencing," signal dropouts at stoplights, and adjacent-channel interference. On AM, it eliminates impulse noise and static, and reduces signal dropout under bridges. Indeed, measurements confirm that HD Radio has broader frequency response and lower distortion than conventional broadcasts, resulting in better sound. And, iBiquity claims, extensive listening tests suggest that the system raises AM radio's sound quality to that of today's FM and raises FM's sound to approach CD's.

In iBiquity's demonstrations, the claim of FM-like sound from AM seemed spot on. The digital audio was cleaner, smoother and-more important-free of static. With FM, which sounds better than AM even in analog, the improvement was less pronounced but still significant, with less interference and slightly more extended highs. Under lab conditions, comparing a CD's sound with the same signal after processing by iBiquity's perceptual coding and decoding system, the processed sound's high frequencies seemed a bit astringent to me on some tracks, too smoothed out on others.