It seems hardly possible -- particularly to those fans who have followed Michala Petri since she first began to record with the Academy of St. Martin-in-the-Fields circa 1980 -- so much time has passed that Petri is celebrating her 50th birthday. There is something about Petri's choice of instrument, her bright, pristine tone and preciousness, that seems in a way eternally precocious and youthful, ever the ingénue. Nevertheless, the half century mark doesn't find Petri planning to receive AARP benefits; rather, she has organized a concert to mark the occasion and recorded it for her OUR Recordings label, which she runs with husband Lars Hannibal. Petri is appearing with a group she is especially fond of, the KREMERata BALTICA orchestra founded in 1997 by violinist Gidon Kremer. From the standard Baroque literature for recorder, Petri picks the "D minor Concerto, Op. 9/2," by Tomaso Albinoni -- which she recorded so winningly with Claudio Scimone and I Solisti Veneti back in 1990 -- and the Vivaldi "C major Concerto, RV 443," another composer to whom Petri is no stranger. Add to that a searing Mozart "Andante" and two freshly commissioned works, "The Ancient Chinese Beauty" from Chen Yi and "Valere lubere (To Say Goodbye)" by Kazakhstan-born Russian composer Artem Vassiliev. The latter has a tension and elegance reminiscent of Edison Denisov's "Variations on Haydn's Canon Tod ist ein Langer Schlaf." Chen's work has an especially exciting third movement, "The Dancing Ink," that snaps along with rhythmic gusto and has Petri's instrument moving through notes that one might think would have no finger holes on the recorder to accommodate them. KREMERata BALTICA gets to show off its stuff as well; they are heard in Nino Rota's "Concerto for Strings" and in some bits taken from Peter Heidrich's popular "Happy Birthday Variations"; in this last segment the extremely quiet and well-behaved audience can no longer restrain itself and joins in with enthusiastic applause and laughter. It's Michala's birthday, a good time is had by all, and so shall you.