The guitarist told Rolling Stone that the end of the band seems to have happened organically.
Sonic Youth's frontpeople Kim Gordon and Thurston Moore separated last month after 27 years of marriage.
Ranaldo said: "I'm feeling optimistic about the future no matter what happens at this point. I mean, every band runs its course. We've been together way longer than any of us ever imagined would happen and it's been for the most part an incredibly pleasurable ride.
"There's still a lot of stuff we're going to continue to do. There's tons and tons of archival projects and things like that that are still going on, so there are so many ways in which we are tied to each other for the future both musically and in other ways."
Ranaldo added: "I'm just happy right now to let the future take its course and I guess I'm kind of thankful that I've got this other [solo] project that kind of came about on its own. It wasn't kind of like, well, 'Oh the band is ending for a while and I've got to figure out what to do'.
"It kind of naturally happened in the course of things so that was a nice way for that to come about. I played my first show the day after Kim and Thurston announced [their split]. That was completely weird."
Sonic Youth's last studio album was 2009's The Eternal.
The band also recorded the soundtrack for French film Lights Out (Simon Werner a Disparu) which premiered at last year's Cannes Film Festival.
It was officially released this year as SYR9: Simon Werner a Disparu on the band's own Sonic Youth Recordings label.
In June, Thurston Moore had suggested that the band would reunite and write new material in the near future.
Watch the Sonic Youth 'Teenage Riot' music video below