Maine public radio listeners are about to get a sound choice.

When the seven-station network begins broadcasting a digital signal next year, listeners around the state will be able to check out two alternatives to the programming they normally hear over the FM airwaves.

That means a listener sitting in his living room at 7 p.m. who isn’t interested in the interview Terry Gross has lined up for that evening’s “Fresh Air” can switch to, say, classical music or perhaps the West Coast edition of “All Things Considered.”

And it means a Saturday afternoon errand-runner who can’t stomach opera can tune in contemporary folk and rock music or an edition of the documentary “Soundprint” or “This American Life” from earlier in the week.

To check out the new options will require a new gadget.

A digital receiver – now priced at about $250 but expected to drop to about $100 by the time the service is available in late 2007 – will enable listeners to gain access to the new choices.

The concept of “multicasting,” as it is called, is already being embraced by commercial radio, said Charles Beck, radio services vice president for the Maine Public Broadcasting Network.

Multicasting is seen as a way for broadcast stations to combat the growing popularity of subscriber satellite radio, such as XM and Sirius.

And unlike digital TV, which, by federal mandate will replace the traditional analog in 2009, digital radio is ready to go now.

“It’s here,” Beck said in a recent interview. He said an alliance of commercial broadcasters is ready to roll out a $200 million marketing campaign to sell the public on its benefits.

To explain how digital radio works on a technical level, Beck likens bandwidth to a “pipe in the air.” The current FM radio signal gets sent through that pipe, but there is room for more.

“The magic of this is, in that pipeline you can have more than one digital signal,” Beck said, and in fact there is room for two more signals.

Public radio members already have been surveyed about their interest in digital radio, and a majority indicated they would buy the new gadget, which plugs into a car or home stereo.

At home, the quality of digital music will be noticeably better, Beck said, though the car version may not.

Members also have been surveyed about the kinds of additional program choices they’d like to hear.

Topping the list are “more classical music and more news,” he said.

One drawback: The digital signal will reach only about 90 percent of areas now covered by Maine public radio signals. And as a person drives to the fringe of one of the frequencies, the digital signal will drop out suddenly and completely rather than gradually weakening.

Beck already has developed three draft program schedules, and he talked to MPBN’s community advisory board.

The only other way listeners would be offered program choices is if MPBN bought other FM licenses and broadcast alternative programming on those frequencies. One station – and its license and frequency – could cost $1 million, Beck said.

And since MPBN simulcasts its programs on seven frequencies around the state, from Fort Kent to Calais to southern Maine, adding more stations would be impractical.

Beck said the conversion to digital transmitters is done. It cost about $800,000, but some of that has been recouped through grants. Another $300,000 to $400,000 will have to be spent.

The Federal Communications Commission has yet to approve multicasting, but Beck said that should come soon, and no opposition is expected.

For information visit www.ibiquity.com/technology/iboc.htm, or look-up IBOC.