Even in transition, Joan Armatrading is one of the more remarkable and invigorating singer/songwriters of our time. Ten years past her acoustic origins, Armatrading has incorporated the high energy trappings of rock 'n' roll without abandoning the urgency and internalized passion that make her eclectic offerings at once sophisticated and unsentimental.

Like Van Morrison and Nina Simone, whose oblique phrasing and ardor she sometimes invokes, Armatrading is a complex, demanding singer who begs for exploration. Her phrasing is almost staccato at times, frugal lines propelled by stop-and-go rhythms into the arena of familiarity. Elsewhere, she is sensually bluesy, hard as nails, as difficult to figure out as a greased Rubik's cube. Her voice is husky, earthy, a rich evocative contralto that can soothe or lascerate at will--and often does, in the same song. Her songs examine the human condition and the fruits, bitter and otherwise, of love and independence.

In her sold-out concert at Constitution Hall last night, Armatrading concentrated on material from her three most recent albums. She opened with "I'm Lucky," immediately setting a mood of lilting irony and subtle soulfulness. The night became a potpourri of grace, wit and inventive, vital music delivered by an artist deserving of far wider recognition. With a dynamic band rocking her past abandon, Armatrading confirmed the audience's belief in her as an artist of rare stature and uncompromising integrity.