Discovering the music of Estonian composer Arvo Pärt (above) for the first time is like stumbling onto a new language that expresses clearly and plainly the previously unthinkable; with a minimal investment, it provides great release. His "Spiegel Im Spiegel" is a work of inexhaustible beauty, his "Tabula Rasa" a piece of intricate challenge. While the former enjoys the spotlight on screen and stage, the latter is a well-loved yet underperformed masterpiece, mostly because of the daunting uphill climb toward violinist Gidon Kremer's untouchable and definitive 1977 recording of this delicate work, blooming as it does with harbored rapture. "Whoever wrote it," muses Wolfgang Sandner in the album's liner notes, "must have left himself behind at one point to dig the piano notes out of the earth and gather the artificial harmonics of the violins from heaven." San Francisco's award-winning New Century Chamber Orchestra performs "Tabula Rasa" in an inspired pairing with Bach's "Concerto for Two Violins and Strings" and Schoenberg's "Verklarte Nacht" on Wednesday, April 11, at Osher Marin Jewish Community Center. 200 N. San Pedro Road, San Rafael. 7:30pm. $28-$42. 415.357.1111.

Adding to the reservoir of chamber music from which to drink is the wonderful Russian River Chamber Music Society, which graciously presents free performances from all over the musical spectrum. Whether with the dissonant glissandos and eerie tape loops of Ethel, presented last year, or the civilized Mendelssohnian veneer of the Amadeus Trio just last month, the RRCMS can be counted on for quality and taste. Next up, New York's Proteus Ensemble perform works by Copland, Carter, Villa-Lobos, Piazzolla, Gershwin, and Rorem on Saturday, April 14, at the Healdsburg Community Church. 1100 University Ave., Healdsburg. 7:30pm. Free. 707.524.8700.

Finally, from out of the pit and onto the stage comes Craig Reiss and the Eos Ensemble, a group mainly comprising members from the San Francisco Opera orchestra. With guest artist Richard Savino on guitar, the quintet will perform works by Boccherini, Piazzolla and Falconieri before bowing out, guitarless, with Shostakovich's String Quartet no. 8 on Thursday, April 12, at the 142 Throckmorton Theatre. 142 Throckmorton Ave., Mill Valley. 8pm. $15-$20. 415.383.9600.

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