DAVID GRISMAN took the familiar acoustic bluegrass instruments and proved you could use them to play any kind of music imaginable. This so expanded the potential of American acoustic instruments that even the prolific Grisman couldn't cover all the new territory. Fortunately, the alumni of his various bands have been busy charting the terra incognita of Grisman's "dawg" music, as he calls it.

Two of his best disciples have been fiddler Darol Anger and guitarist Mike Marshall, who were in Grisman's band for six years together. They pioneered the folk-jazz that made Windham Hill Records possible, and now they've given that label some of its most substantial music ever with their latest album, "Chiaroscuro."

It shows them less concerned with pronounced rhythms than their mentor and more interested in single-note excursions. But fortunately their improvised lines are so melodic that the pieces never lose their momentum. The duo is joined by Grisman alum Todd Phillips on bass, Anger's wife Barbara Higbie on synthesizer, Andy Narell on steel drums and Virginia's Michael Manring on electric bass. But the duo's fiddle, guitar and mandolins still predominate. Their rapport is uncanny as each repeatedly picks up the other's improvised idea and extends it in a new direction.

Mark O'Connor was an eight-time national fiddle champion before joining Grisman's band. On his new solo album, "Meanings Of," O'Connor plays nearly every instrument ever asociated with "dawg" music. Except for some guest percussionists, it's pretty much a one- man show. As a result, it doesn't have the sense of lively interplay that "Chiaroscuro" enjoys, and O'Connor sometimes overloads the tracks. Still, he is such a virtuoso on any stringed instrument that this record is scattered with dazzling moments.

DAROL ANGER & MIKE MARSHALL -- "Chiaroscuro" (Windham Hill, WH-1043);

MARK O'CONNOR -- "Meanings Of" (Warner Brothers, 9 25353-1). Anger, Marshall, Barbara Higbie and Michael Manring appear with O'Connor as special guest, Friday at the Barns of Wolf Trap.