The aura of seeming effortlessness around Johann Sebastian Bach's craft sometimes obscures that the Baroque was a time of aesthetic extremes. Some of that can be sensed in the contrast between the era's most prominent keyboard instruments: the harpsichord's unavoidable decay, the organ's unflagging sustain. (Tellingly, the piano, mediating between those poles, only gained traction as the era wound down.) On Saturday, at the First Lutheran Church, Luca Guglielmi used Bach's music to navigate those two instruments' divergent interpretive and technical claims.
The concert — presented by the Boston Early Music Festival — was organized as two imaginary recitals, Guglielmi's conception of how Bach might have shown off each instrument. On the harpsichord — each note quickly evaporating, with only the variation in volume between two manuals to work with — Guglielmi alternately avoided or emphasized concurrence to make musical points. In the Suite in C minor (BWV 997, better known today in its version for lute), Guglielmi's playing was all rolls and breaks, notes nudged into the spotlight by being knocked slightly off the beat; the whole undulated like a loose cat's-cradle of melodic lines.
The Andante from the Italian Concerto (BWV 971) had the same cast, but the faster outer movements had more metronomic drive, chords coordinated into raspingly percussive punctuation. That noise turned horizontal in the Chromatic Fantasy and Fugue (BWV 903), Guglielmi running notes together at a pace that produced a humming, demonic rustle.
Switching to organ for the second half, Guglielmi adopted some of the same expressive strategies — though not always with the same results. In a Prelude, Trio and Fugue in C major assembled from disparate parts — the Prelude and Fugue from the first and second books of the Well-Tempered Clavier, respectively, the trio from the BWV 529 Trio Sonata — accents were by addition: a slight extra delay before an underlined note, a slight lengthening of the note itself. It created an unsettled, stop-and-go quality, a veneer of hesitancy over the rhythm.
That push and pull continued in the Fantasia in G major (BWV 572) and the first of the four Duetti from the third Clavier-Übung (BWV 802-805), but in the other Duetti, as well as the A minor Prelude and Fugue (BWV 543), Guglielmi created expression not by appending time, but taking away sound: The notes stayed fixed to the rhythmic grid, but the space between them varied. Bach's counterpoint — and momentum — piled up, thrillingly, in strict time. Sometimes the most extreme effect is simple implacability.