If your deepest desire is to return to the 1950s — the decade that witnessed the invention of rock ’n’ roll — you might as well go time-traveling to the ravings of The Dex Romweber Duo. Back in the ’90s, Romweber and his band Flat Duo Jets specialized in rockabilly that included plenty of twisted surf guitar. He’s still at it: Romweber and his sister Sara have perfected a cheerfully demented variation on the guitar-and-drums format. Their new full-length Is That You in the Blue? finds the Indiana guitarist and singer bellowing out such tunes as “Jungle Drums” over some very strange accompaniment — their version of Ary Barroso’s venerable “Brazil” achieves the unintentional harmolodic density that garage-rockers have been seeking for years. “Gurdjieff Girl” is a nifty post-Dick Dale instrumental, while “Homicide” effortlessly combines science fiction and rockabilly. Heck, maybe the ’50s really were more fun.