Known for his magic in the Stax Records studio in the sixties, the Tennessee keyboardist—whose career comprises performances with not only his group, the MGs, but also such artists as Neil Young and Willie Nelson—is a special guest at this month’s South by Southwest Music Festival, in Austin.

What’s your proudest musical moment? The first time I heard “Green Onions” on a radio station in Memphis. That moment was recently replayed as I was [listening to the radio on] the Golden Gate Bridge. The thrill has not diminished at all.

The song was almost an afterthought. We arrived at the studio to back up an artist that didn’t show. We started jamming on a riff that I had been playing around with on piano, which turned out to be “Green Onions.” I played it on a Hammond organ to match another song we had recorded.

Describe a Stax session. I started in the tenth grade; I’d go after school. My first session was for Rufus and Carla Thomas. A writer would have a song idea and team up with a lyricist or musician; then the band would record it. Sessions went until six or seven, when the musicians left for their club gigs. Once [Stax] became successful, we quit our club gigs and sessions ran later, sometimes most of the night.

How did you meet Willie Nelson? Willie rented the apartment underneath mine in Malibu, in 1976. We started jamming at night on his or my deck by the beach. We ended up in the studio later that year and recorded some of those songs. It became the Stardust album.