By all rights this 1970 album — featuring a genre that had been effectively obsolete since the days of silent film, a then-completely obscure composer, and a performer best known as a Bach scholar and Beatles parodist — shouldn’t have even registered as a blip on the radar, let alone become the first Nonesuch album to sell more than a million copies. Its improbable success is a testament to Rifkin’s meticulous musicology, canny curation, and the understated pianism with which he teases out the simultaneous simplicity and complexity of Joplin’s innovations in ragtime.