THE clearest sounds ever broadcast into the home are being heard these days on a public station here, and it may signal a whole new radio era -- eventually. The three-month experiment in ``digital audio'' needs a TV channel to carry the sound and requires expensive home equipment to be heard. The listenership is tiny, but the results are impressive.
It's as if listeners ``had a compact disc player in their living room,'' says John Voci, operations director of WGBH-FM, the public radio station conducting the test with its sister UHF-TV station, WGBX-TV. ``You don't hear any of the transmission noise or hiss. This is the first time listeners with the right equipment can receive a broadcast digitally in their home. That is what is very different.'' And Dave MacCarn, engineering director for WGBH television and radio, compares the difference to that between FM stereo and AM radio, or between color and black-and-white TV.
Their claims were dramatically confirmed during a recent demonstration at the public station. The voice of music-show host Ron Della Chiesa was heard over powerful speakers on conventional FM. Then the digital signal was switched on, and his voice suddenly became transparent and distortion-free, revealing every lurking tremulo unnoticed on FM. The dead air between his words -- the total absence of background sound -- was startling and a little uncomfortable at first. His words seemed to float separately in space, as though coming from nowhere.
The concert music that followed was no less striking in its acoustic purity and impact. ``It has a much broader frequency response,'' Mr. Voci explained later by phone, ``from your lowest sounds to your highest sounds, and you've got a much broader dynamic range. You're able to hear the quiet passages as well as the very loud passages.''