The music of three of Bach's myriad sons was featured yesterday at a concert given by the Wondrous Machine at Christ Church, Capital Hill. The Wondrous Machine (its name refers to the raucous organs that stunned the ears of 10th- and 11th-century listeners) is a nicely balanced, anything but raucous, chamber group whose focus, as seems to be the current fashion among early music ensembles, is on the late Baroque and early Classical periods.

For yesterday's concert there were violin, viola, cello, oboe and fortepiano (not to be confused with its more powerful descendent, the piano) in various combinations.

In the capable hands of James Weaver, the fortepiano, without the metal frame of the modern instrument and therefore more lightly strung and more delicate, took its place as an equal partner in the ensemble, often absorbed into the musical texture. Its presence filled in the harmonic outlines and sometimes added a rhythmic edge, but never dominated the sound.

Stanley King's Baroque oboe, with a timbre that bridges the tone of the trumpet and the modern double reed, seemed more poignant than its modern counterpart.

The performances were nice, if a little self-effacing, and the musical selection did a good job of underscoring the great variety of styles that were concurrent during the middle of the 18th century.