From the time they initially met in the fall of 1962, and for the next few years—until the first stirrings of rock and roll notoriety beckoned—singer Janis Joplin and guitarist Jorma Kaukonen occasionally collaborated at hospitable venues in the Bay Area. On an early summer morning in 1964, they met up at Jorma’s abode to rehearse for one such upcoming gig in San Francisco. Kaukonen pressed the record button on his tape recorder, while his wife Margareta pecked away on a typewriter at the other end of the room—not trying to provide clickety percussion, just immersed in her own busywork. The resulting 23-minute recording has been in circulation among collectors of bootleg recordings for decades (a couple of songs even made it to a Joplin compilation album), a souvenir of a long-ago time when two young, ambitious and prodigious talents— little more than acquaintances, really—worked on their craft for the sheer love of it. There are only seven numbers here in all, most of which are by now familiar to anyone who’s spent any time investigating the standard blues repertoire. What’s most startling is just how fully formed these two artists already were, well before their names were known globally. Joplin is a born blues stylist, her sensual, gutsy interpretations imbued with all of the soul and wisdom of the older singers she idolized. Kaukonen, a fingerpicking acoustic guitar master, is natural and knowing as well. On songs like “Trouble in Mind,” “Nobody Knows You When You’re Down and Out” and “Hesitation Blues”—sounding clearer and crisper here than ever before, albeit still homemade—they form a blues duo as pure and engaging as any before or since. And yes, although it was not their intention, some serious history was made that day.