Mark Kroll, renowned harpsichordist who has played with the Boston Symphony Orchestra since 1979, will give a free recital at 7:30 p.m. Thursday, Oct. 15, in the Spanos Theatre at Cal Poly. Kroll, also a fortepianist, has enjoyed a career spanning more than four decades. He has performed throughout Asia, Europe, the Middle East, and North and South America, winning critical praise for his expressive playing and virtuosity.