He had this whole aquatic theme that came out of something we’d talked about when he was working on “Swimming.” I’d noticed he mentioned water a few times in the lyrics, and then that grew into all these discussions about water and what it sounds like that became kind of a running joke. There were supposed to be three albums: the first, “Swimming,” was sort of the hybridization of going between hip-hop and song form. The second, which he’d already decided would be called “Circles,” would be song-based. And I believe the third one would have been just a pure hip-hop record. I think he wanted to tell people, “I still love this, I still do this.”

What did you see as your role on the album? Were you solving a puzzle? Or trying to discern what Mac would do?

I mean, you can’t, really. You can’t speculate about anything. And every artist changes their mind every two weeks. So I was just trying to figure out what I could get out of the way of, instead of trying to “invent” a track or a song, or make something that wasn’t a song seem more like a song. He had talked to me a lot about what he wanted sonically. Like, “I want this to feel wider,” or “deeper.” So, for me, I felt like, “O.K., these are technical jobs that I can do.”

There’s been some speculation about whether there are Ariana Grande vocals on “I Can See.”

I believe there are. Somebody just told me something about that, some kerfuffle. I mean, that was a pre-existing track. There were a few songs the family gave me that he’d been working on independently that I thought fit thematically with what we had worked on. “I Can See” was one of those, also “Complicated,” “Blue World” and “Everybody.” I played some things on those tracks to make them feel like the others, but those vocals were already there. It wasn’t like an executive decision or anything.

The emotional content of the album — his struggles with depression and anxiety — would be poignant even without knowing his fate. How affected were you by the lyrics?

When I heard “Once a Day” on that plane, it was like a knife in the heart. I cried even when I was in the room with him recording it. And then, later when I was back in the room adding a guitar part or something to finish it, I would have to listen very closely to the vocal and it would just pulverize me. He was clearly trying to sort through his demons and was just being very, very honest, not trying to hide any of it. I feel like the album is a clear picture of somebody with those troubles who is funny and intelligent and was trying to look at them critically.