When Anita Baker sang her soul-jazz hits at Wolf Trap last night, she quickly established her themes of adult romance in a deep, smoky alto. Before long in each song, though, she slipped out of the ballad melody into a note-slurring moan or a fluttery sigh, as if love had dislodged her from the moorings of reason and sent her into an emotional free fall. It was a brilliant device -- using her total vocal control to mimic the loss of control caused by love -- and her songs often transcended words to become twisting, cathartic, pure sound.

Unfortunately, Baker relied on this same device for nearly every song last night, making one indistinguishable from the next. She put so much emphasis on her improvised moans that she never really sold the lyric on any one song. That may be just as well, for her material -- especially her newest songs -- was the weakest link in the concert.

She compensated on a few songs by providing a context in the form of long, spoken introductions. She led into "Watch Your Step," for example, with a story about falling in love at 16 with a pushy 18-year-old boy. She then built the song into a feverish improvised duet with alto saxophonist Everette Harp, who in turn pushed Baker into more aggressive, more focused scat singing than usual.

The four Perry sisters, who provided the harmony vocals for Baker, have recorded three albums under the group name of Perri, and they assumed that role in the opening set. They combined gospel shouting, R&B dance rhythms and pop material much like the Pointer Sisters, but Perri's strong, energetic voices sprawled without direction and failed to shape their amorphous sound into well-defined songs.

Anita Baker and Perri return to Wolf Trap tonight.