Terry Riley’s “In C” is generally considered the founding document of the musical movement still (if somewhat sheepishly) called “minimalism.” That’s certainly what it sounded like Saturday evening in Silver Spring, where guitarist Anthony Pirog led a 22-member ensemble through an assured performance of the 1964 composition. Presented for free at Veterans Plaza (aka the skating rink), the concert was part of the annual Sonic Circuits Festival of Experimental Music.

With its steady cadence, shifting patterns, staccato notes and shimmering effects, the 55-minute rendition suggested such Steve Reich pieces as “Music for 18 Musicians.” This was not especially surprising, since Reich subsequently developed the principles of “In C” more than Riley did. And it was Reich, as a member of the ensemble for the composition’s 1964 premiere, who suggested that it needed an unwavering pulse — provided on Saturday by Kenny Pirog’s cowbell. This seems to reflect Reich’s interest in Balinese gamelan more than Riley’s principal influences, which include jazz, Indian classical music and John Cage, whose compositions often rely on chance.

Cage’s methods did shape “In C,” which differs from the work of Reich (and Philip Glass) by leaving certain decisions to the performer. The piece comprises 53 musical phrases, which must be played in order but can be repeated as many times as the individual musician chooses. That’s why the many recordings of “In C” vary from about 20 minutes to nearly 80 (the time limit for a CD). The Pirog ensemble’s version seemed a suitable length, although there were mesmerizing passages that might have been fruitfully sustained for, oh, another hour or two. The performance, which was expertly mixed, held the audience’s attention despite competition from another chance-generated sound source: the traffic on Fenton Street and Ellsworth Drive.

The group consisted mostly of Western orchestral instruments, supplemented by accordion, mandolin, synthesizer and the conductor’s guitar. While Riley’s score doesn’t specify instruments — another Cage-like touch — its jumpy eighth-note melodies highlighted the ensemble’s glockenspiel, vibraphone and mandolin. But the prolonged tones of the string and wind instruments provided a lush bed for the sharper timbres, and were true to the composer (known for his organ, saxophone and vocal drones). There is no right way to score “In C,” but the textural contrasts provided by Pirog’s troupe were true to the spirit of this vastly influential piece.