Let's see - listening to the first of sixteen CDs of the Juilliard String Quartet, the Early Recordings from the late 1940s to 1955, so all mono. But it's the material that's fascinating and a must-have, plus the quartet plays beautifully. You get six Bartok string quartets, and album of Darius Milhaud, an album of Berg, four Schoenberg quartets - but it's all the American composers that make this so special - Copland, Schuman, Mennin, Foss, and others of that era. Amazing stuff in excellent sound.