“It’s an epic, isn’t it? There’s one part in the piece where we’re playing in 10/8. That was Carl’s doing. Even The Beatles had used time signatures in 7/8, so I guess that going somewhere like that wasn’t too unusual. But Carl was very forward-looking in how he wanted to push time signatures. He was sitting backstage with a practice pad, and he started hitting out this 10/8 rhythm. It sounded right, so that got me to writing Tarkus.

“The writing was very painstaking. The whole thing was composed on an upright piano in this little apartment in London I was living in at the time. I wrote it out on manuscript, too, which not many people do. I have to say, it wasn’t intended to project any pianistic bravados, like, ‘Oh, my God! This keyboard player is fantastic.’ Nothing like that. I was just trying to get a point across.

“It starts off with The Eruption, which was the first thing that got Greg’s attention. He said, ‘Yeah, well, that’s a nice prelude to a song.’ But as an entire piece, he wasn’t very enthusiastic. It took some convincing to get us to do it. When it came time to produce it, that’s when Greg went along with it, and by then he’d stuck his producer’s hat on, so he was really OK with it. The rest of the piece came together quite easily, actually. Once Greg and Carl got the 5/4 down, and then we had the 10/8 section, everything else flowed.

“We rehearsed it for a week or so in the studio. Greg and Carl don’t read music, so we ran it down quite a bit. They formulated it and memorized it. Sometimes we rolled tape, just in case we got something worth keeping. We ran it down live as a trio, got a take, and then we listened back in the control room for parts that needed overdubs. ‘What about a gong here? What about a portamento sweep there?’ Greg and Carl had lots of cool suggestions.

“It’s a well-composed piece. I made sure that the fourths and fifths were working together. There’s a good sense of continuity to it. I was searching for what one of my heroes, John Coltrane, wanted to create – walls of sound. I thought, I can dig that, but I’m going to go another way to get that across, with electronics and the Moog synthesizer and everything else.

“I had the Moog modular synthesizer for this, which I’d started using in 1969. It’s being renovated in California right now. It’s a killer, let me tell you. Quite an instrument, the Moog.”