Part of the pleasure of exploring Sonic Youth is hearing how their instrumental passages evolved over the years, from the compacted intensity of stuff like “Expressway to Yr. Skull” to the looser, more meditative sound of “The Diamond Sea” and “Wildflower Soul.” Recorded between 2000 and 2010, the five tracks on In/Out/In—lengthy, improvised, focused but serene—are, at the least, interesting archival material from a band rarely ever less than great. But they also form a Venn diagram of the disparate territories the band yoked together: classic-rock groove (“Basement Contender”) and free-form noise (“Social Static”), music for headbanging (“Out & In”) and for daydreaming (“In & Out”). At the end of the punk-rock rainbow, they found the hippie’s freedom; at the horizon of the avant-garde, they found a backbeat.