Sonic Youth have a song "The Diamond Sea" which is a 20-min+ recording on the WASHING MACHINE album and generally about that long or longer in their live performances. It's very similar to the Grateful Dead's "Dark Star" which the band explores improvisationally with loads of Sonic Youth noise and well loved by fans as a live perf.
Sonic Youth have approached us on wanting to work with John Oswald, who is very interested, on making a similar new mix of "The Diamond Sea" from loads of live perfs of the song as a RSD release.