What do Earth, Wind & Fire and Michael Bublé have in common? Mega music producer David Foster. Before he became famous for his presence on reality TV, Foster brought his soaring sensibilities and steely concentration to artists like Barbara Streisand, Whitney Houston, and Chicago. Documentary filmmaker Barry Avrich turned a camera on Foster for the Netflix film, “David Foster: Off the Record,” and tracked the difference between control in the studio and the chaos outside of it. Avirch discusses what draws him to such subjects when he stops by “The Treatment.”