After a decade-plus hiatus, Sir Paul revives his low-profile, weed-scented collaboration with superproducer Youth (U2, the Orb), retrofitting their abstract electronica with good ol’ psychedelic rock for the ex-Beatle’s headiest music in years. “Nothing Too Much Just Out of Sight” throws “Helter Skelter” hollering over electric blues. “Two Magpies” joins “Blackbird” in McCartney’s folksy aviary; “Sing the Changes” is catchy, woozy pop. The set peaks with “Travelling Light,” a magical mystery tour of reverbed chants, slide-guitar swoops, kalimbas and chimes. It’s freak folk by a forefather.