sep1704

Radio AM to FM: September 17, 2004

Less Talk, More Interference

KFI (640 AM), which once prided itself on having one of the cleanest, highest-quality audio signals in Los Angeles -- and in fact was an early adopter of AM stereo -- recently started broadcasting Ibiquity's so-called in-band, on-channel digital system. Also known by the trade name HD Radio, the system forces the analog signal to be limited to a high end of 5 KHz and causes massive interference to second-and third-adjacent channels, the weak stations that immediately surround 640.

To be fair, most people won't notice the audio bandwidth limitation. The audio response of most AM radios over the past few decades has gotten progressively worse, leaving most people to think that AM sounds bad due to the band rather than the radios. Truth be told, AM is actually capable of fidelity higher than current FM, outside of problems with natural and manmade static.

Unfortunately that static, and AM's tendency for long range reception, causes reception problems that are most easily handled by limiting the frequency response of the receiver instead of using modern designs that can get around the problems. Those few who own a good AM tuner know how good AM can sound.

Ironically, it is those of us who believed in AM radio and own good AM radios -- the Denon TU680NAB, the Carver TX11a/b or even a GE Superadio III, for example -- who are getting reamed by KFI's move. HD Radio makes AM stations, as received on a good receiver, sound absolutely awful.

And it doesn't just stop there. As mentioned, adjacent stations are either missing, or have interference, due to the digital sidebands. As more stations start using HD Radio, fewer and fewer stations will be received in any particular location. Some predict that the AM band will be made completely useless at night, if HD Radio is ever authorized for nighttime use. The issue is so great that Canada is asking the FCC to look into it, due to the fear that interference from across the border will cause their own stations to become unlistenable.

In the meantime, if KFI sounds bad on you radio, it doesn't mean anything is wrong. It means you have a good radio ... and that KFI has given up clean analog audio.

What is HD Radio?

HD Radio is an attempt to increase the fidelity of both AM and FM broadcasts, within the regular broadcast bands. AM is supposed to sound "as good as FM," while FM is supposed to be "CD quality" (true audiophiles must be groaning at the claim, as CDs are not known as the high end of sound reproduction by any means).

Opinions are strong on both sides; personally I am leaning toward the nay sayers, who believe that HD Radio really doesn't sound that good and that the system causes far too much interference, both on AM and FM. On the other hand, engineers such as Tom Ray of WOR/New York are convinced that HD Radio is the best system currently available. WOR was the first full-time AM HD station on the air in America; I plan to interview Mr. Ray as soon as he has time in his schedule.

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