FOR SOME years there has been a great vogue for the Baroque, although some of the critical comment has resembled that wonderful M*A*S*H routine in which Radar sighs, "Ah, Bach!" Until Monteverdi, it was the accepted wisdom that music had reached its pinnacle, that it had become the ars perfecta, to be followed only by more of the same. Monteverdi created a revolution in technique, structure, and idiom. It is not stretching it to say he was the father of modern music, at a level perhaps ...