This just popped up on my Facebook newsfeed from ISB 1984. I think they are probably playing one of the Bottesini Arias for bass and singer.
Bass Circle from left: Jeff Bradetich, Knut Guettler, Roma Vayspapir, Ed Barker, John Clayton, Rodney Slatford, Henry Leow, Paul Ellison, Nico Abondolo, and Joseph Guastafeste. Edgar Meyer is the soloist next to the singer in the middle. I don’t know who the singer is though. Orlando Donado is the conductor.