Boston — People in Jackson, Miss., are scratching their heads as the classical music program on station WFMT-FM yields an unexpected bonus: Chicago traffic reports. It's a phenomenon that's becoming more common as a new sort of broadcasting develops - cable radio.
Cable radio is the cousin of cable TV, an additional service that cable subscribers can receive along with television. As for Chicago radio station WFMT , its classic music programming is now on cable in 273 cities across the country , although station president Ray Nordstrand reports that some people still can't understand why they're being kept so up to date about rush hour in the Windy City.
Up to now, cable radio (or cable audio, as it's also known) has been overshadowed by the blooming of cable TV systems, many of which at this point don't offer audio service. But cable radio has meant, and will mean, more variety of formats for listeners and a further diversification for the industry.
New developments in broadcasting technology, particularly Direct Broadcast Satellite, could spell future competition for this new type of transmission. But today cable audio programs range from classical music (on WFMT) to multicultural programming (on the Nationality Broadcasting Network) to jazz (on Los Angeles's KKGO-FM).
Among the advantages of cable radio:
* Audio clarity. Like conventional radio, cable audio can be heard on stereo, though an additional hookup is needed. Distortions inherent in FM and AM broadcasting are eliminated, however, and only cable radio can take full advantage of the new digital sound.
* Versatility. Because it costs so much less to broadcast by cable, big audiences won't be needed to support programming. It's therefore anticipated that a wider variety of programs, often for diverse tastes, will be offered. Already a number of ''radio stations'' are broadcasting entirely for cable - some with some unconventional formats.
* Continuity. Daytime radio stations will be able to continue broadcasting - over cable - around the clock. Some stations are on FM and AM and cable simultaneously, bridging video entertainment with radio.
But don't throw away your regular radio sets yet. Cable radio has some severe limitations, one being that you can't take it with you. Because the receiver must be attached to the cable hookup, it can't be packed away for a weekend invasion of the wilderness or be a chatterbox on the drive home from work. It usually costs a monthly fee as well. And, of course, most homes still don't take cable.
''Cable radio doesn't pose as much of a threat to broadcast radio as cable TV poses to broadcast television,'' remarks Dennis Waters, editor and publisher of New Radio, a newsletter. Industry figures show that about 40 percent of radio listening not done at home.
Wayne Cornils, radio vice-president of the National Association of Broadcasters, says, ''It'll grow slowly. Its big potential is in ethnic types of programming. For instance, a Polish radio channel.''
Already a number of cable radio stations are offering ''ethnic'' programming. COOL-FM, a 24-hour soul and gospel cable radio station in Fort Wayne, Ind., is one. Lewis Dinwiddie, founder, owner, and general manager, remarks, ''It's (cable radio) a brand new frontier.'' He believes cable radio will move into wherever there's a gap in AM and FM programming - including ethnic programming. ''The overhead is so low you can serve a very limited community.''
On the other hand, many sections of the country aren't able to support some radio formats, like classical music. That's where something like WFMT comes in. WFMT has been on the air for 30 years and on cable the past four. Widely heralded for format and its state-of-the-art equipment, the station features mostly classical fare, often with live performances.
There's also SCAN, which distributes, along with NBN, five 24-hour audio services called ''Music in the Air,'' featuring country and western, comedy, Broadway/Hollywood music, big-band sounds, and tunes from the '50s and '60s. As well, Cable's MTV (Music Television) and Home Box Office movies can be heard in stereo, although these progams are not intended to be strictly audio.