There's something intoxicating about the Elias String Quartet. It was no mystery that the group was able to cast a spell Tuesday night in a newish Sally Beamish work, the String Quartet No. 3, with those spiritual Gaelic atmospherics. But for its Philadelphia Chamber Music Society visit, the Elias brought Haydn, personalizing the F major, Op. 77, No. 2 quartet to the point of instantly rendering every other performance in the listener's memory as but a pale stab.

The third movement "Andante" was a landmark statement, intensely absorbing, exquisitely considered - a piece in itself, really. The main tune seems unremarkable, an understated if proud march. But the Elias gave it a storyline. The tune keeps repeating, but around it grows all manner of embellishment, like a pilgrim on a journey. The Elias tended these developments so lovingly that when the arrival point came and went, and the spare version of the theme reappeared at the end, simple and muted, it had the paradoxically powerful impact of a church organ wheezing in the distance.

Remarkably, other moments Tuesday night came close. The Elias uses vibrato, but not automatically, and sometimes not at all, a strategy that, combined with soft attacks and a very blended sound, gave the whole of the Haydn a charming, ancient quality.

How would this sound lie upon Schumann's Piano Quintet in E flat major (Op. 44)? Here the players shifted identity. Still blended, still magnificently colored, the quartet absorbed the addition of pianist Jonathan Biss like a shared confidence. Dialogue is written into the piece, with the piano sometimes an adversary of the strings, and other times re-creating their sounds from the keyboard. The solo lines were like brief concertos - cellist Marie Bitlloch and violist Martin Saving were particularly stirring.

With Biss' imaginative sense of phrasing, the group not only solved transitional moments that trip up others, but also clarified Schumann's emotional intentions to stunning effect.