The Association for the Advancement of Creative Musicians (AACM) was formed in 1965 to nurture jazz's most progressive improvisationalists under the rubric of "Great Black Music, Ancient to the Future." Few have lived up to that motto with such theatricality as Henry Threadgill. As composer, saxophonist, and flutist, he has transcended many boundaries, writing and playing what he calls "mutable music," including threads of circus marches, classical, world beat, and ragtime. On Sunday night at the Christ Church Neighborhood House, Threadgill and the members of his Zooid ensemble never stopped mutating.

The show was the second of the Ars Nova Workshop "AACM/Great Black Music" festival, which continues Saturday with saxophonist Roscoe Mitchell and Monday with Tortoise guitarist Jeff Parker (for details:

From the quiet opener, "So Pleased, No Clue," Threadgill and company went out but never too far out. His compositional acumen called for decorum in every odd timbre, coolly expressive passage, and bold counterpoint. In "So Pleased," each member dotted Threadgill's blank canvas (a twitch of Liberty Ellman's acoustic electric guitar here, a restrained honk of Jose Davila's tuba there) until the dots connected.

All the while, Threadgill played his alto sax slow and low, with but a few high squeaks slipping by. During "A Day Off," a slight bossa nova element entered drummer Elliot Humberto Kavee's cymbal rides, followed by Christopher Hoffman's hard-bowed cello and Threadgill's layered, circular sax line. A closing maelstrom brought together each musical element at once. Certainly, Threadgill's usual leanings into circus-inspired melody and skewed Latin music (the Spanish-flavored flutterings of Stomu Takeishi's oversized acoustic bass, for example) were in evidence, occasionally sudden and brash. But his bearing called for implosion rather than explosion, and every manic expression was pulled gloriously inward.

By the time the sextet hit the softly unwound "It Never Moved," everything had moved, but subtly. Ellman showed he was a plucky jazz guitarist of Johnny Smith-like punctuation, and Threadgill threaded himself with passion, tenderness, and grace through the calm interplay.