Three string players, a pianist and a drummer begin playing what sounds suspiciously like old-fashioned chamber music. Then things change. Violinist Matt McBane, who is also the composer, wanders enticingly afield. Drummer Adam Gold taps rhythmic encouragement. Pianist Mike Cassady adds licks.

This is the ensemble Build, performing in the kickoff to the fifth annual Carlsbad Music Festival, which lights up this California seacoast town through this weekend. Carlsbad exemplifies the way a young generation of composers rethink accepted musical pigeonholes -- classical versus pop, chamber versus orchestral, harmony versus noise -- that fogeys like me once held sacred.

Build builds on the value of the mix: the freedom of a rocker to fashion a weirdly twisting tune; the classical violinist's (McBane is one) love of the enchanting melody and the dizzying scale-passage.

California-born McBane, 28, journeyed with his fiddle and his University of Southern California composer's degree to New York, formed his group of like-minded spirits in 2006 and pushed his way into club dates, art spaces and concert halls. A disc on the New Amsterdam label offers nearly an hour's worth of the group's skittery, unpredictable and utterly charming musical inventions.

Nonchalance Carlsbad is McBane's hometown. He began his modest festival in that San Diego County town with family and local support, enlisting other young composers and groups with similar nonchalance toward the old musical definitions. Last week's concert also enlisted two such groups: the percussion ensemble Red Fish Blue Fish, based at the University of California-San Diego and the up-and-coming Calder String Quartet, quite possibly the finest -- and certainly the most adventurous -- American chamber group.

Highlight of the percussion segment was ``Third Construction'' by John Cage, the grand nose-thumber himself and patron saint of Carlsbad festivals and its ilk, past and future.

Carlsbad Festival concerts continue on Sept. 26 and 27 at 8 p.m. at Schulman Auditorium in Carlsbad with pre-concert talks one hour before. For the final program, on Sept. 28 at 2 p.m. in Schulman, the program consists of music by another California immortal, Harry Partch, who designed and built his own instruments to elucidate his iconoclastic theories on harmony. These gorgeous instruments will be on hand, and they're alone worth the trip.