First and foremost is a remarkable sense of group control. From the outset of this weekend's program, the passagework in Haydn's Quartet Op. 76, No. 1 was perfectly unified, crisp and sparkling. Both the Haydn slow movement and that of Beethoven's Quartet Op. 18, No. 2 featured meticulously balanced chords and a sound blended carefully down to the last grain. Mendelssohn's Quartet Op. 44, No. 1 was full of surging energy and forward motion. The quartet has also rediscovered its unique way of zapping an individual phrase or even a single accented note with electricity, as if flipping a switch.