It’ll be a real toss up as to what’s lovelier at the Hatch Shell on Thursday night: The view of the Charles River on a late summer’s evening, or the music drifting down from the stage. The free show features indie stalwarts Spoon (right), the quartet from Austin, Texas, that broke free of a reputation for slightly predictable indie rock with their 2002 album, ”Kill the Moonlight,” which found the band reveling in a cool, inventive groove. Band leader Britt Daniel and company haven’t looked back since, and 2004’s ”Gimme Fiction” expanded their sound even further, into a luscious mix of tautly orchestrated slow jams and brisk, funk-laced rave-ups, all drenched with Daniel’s nasally, effectively jaded vocals. They’re joined by Longwave, a group of atmospheric rockers from New York City that creates hushed, moody soundscapes, only to shatter them with blasts of wiry, distorted guitar. Their third album, this year’s ”There’s a Fire,” is a gorgeous, emotionally resonant mix of hushed confession and bombastic rock grandeur.