As the child of an unmusical and abusive father, Edgard Varèse (1883-1965) dreamed of "a sound set free." But Varèse's path, which led him first to Paris, then Berlin, and then New York (where, for a time, he worked as a piano salesman), was a long one.

Only toward the end of his life, when electronic technology finally caught up with his volatile imagination, did the composer take his place as one of modernism's grand old men, lauded by the likes of Pierre Boulez and Frank Zappa. Even now, his ferociously individual music, which fits neatly on two CDs, is seldom programmed. Hence this weekend's performances by the St. Paul Chamber Orchestra of Varèse's "Octandre" and "Density 21.5," provocatively juxtaposed with Mozart's grandest concerto and his darkest symphony, have the makings of an event.

Amounting to some 10 minutes of music, the SPCO's introduction to Varèse could scarcely be gentler. Earplugs are unnecessary: The composer's signature siren is nowhere to be found, his characteristic phalanx of percussionists is likewise absent. But the man's bracing, sometimes abrasive spirit is intact. Varèse, never modest, said he wanted to emancipate noise. He did no less.

In "Octandre," guest conductor Hans Graf led the octet of musicians with panache; the work's "nervous" sections (so marked in the score) were vividly realized. In "Density 21.5," Varèse's only surviving solo piece (and a hoop that every serious flutist must jump through), Julia Bogorad-Kogan, the SPCO's exceptional principal, offered both high drama and a remarkable range of timbres. Written for a platinum flute, the music seemed to deepen in color by being played on Bogorad-Kogan's gold-copper-silver instrument.

Against the backdrop of Varèse, Mozart sounds a little different. What musicologist Edward Lowinsky called Mozart's "dynamic asymmetries" -- irregularities of rhythm, harmony and phrase -- come to the fore. This proved true on Friday in both the regal C-major Piano Concerto, K. 503, and the tense, anguished G-minor Symphony, No. 40. To the concerto, soloist Jeffrey Kahane brought a feathery touch and a knack for stylish ornamentation. And in the symphony, Graf, a Mozartian of great distinction, worked miracles of line and balance -- his account of the third-movement Trio, spare and pastoral, was especially haunting. The orchestra played superbly throughout.

With these concerts the SPCO bids farewell to retiring principal viola Sabina Thatcher, who joined the ensemble in 1989, and who has been a memorable soloist and chamber player on many occasions. We salute her and wish her well.

Larry Fuchsberg writes regularly about music.