Saxophonist Sam Rivers was a towering figure of the avant-garde. His recordings for Blue Note, Impulse and Improvising Artists showcase his remarkable facilities as an instrumentalist, composer and improviser, skills he was able to develop even further at his freewheeling New York City jazz loft, Studio RivBea, in the 1970s. Rivers’ trio with bassist Dave Holland and drummer Barry Altschul was captured on tape during a 1978 performance at Keystone Korner in San Francisco, and is now being released on the album Ricochet (NoBusiness). Comprising one long-form improvisation, the piece begins with Rivers’ incisive soprano saxophone conversing with Holland’s swift pizzicato and Altschul’s dramatic thunder. Over the course of the nearly hour-long performance, Rivers switches among soprano and tenor sax, flute and piano; Holland trades fingers for bow and bass for cello; and Altschul continually ratchets up the excitement from behind his drum set, eliciting ecstatic vocal whoops and cries from the saxophonist during his solo. The musicians first came together on Holland’s 1972 album, Conference of the Birds, but recorded as a trio only twice on obscure European labels. So, Ricochet — culled from Rivers’ own collection — represents a rare aural document of the group, as they would have sounded toward the end of the 1970s. It’s a remarkable find, and with luck, not the last undiscovered gem from Rivers’ archives. Holland and Altschul continue to make challenging music, while Rivers, the elderstatesman of the trio, died in 2011 at the age of 88.