Jem Aswad Senior Music EditorFifteen-odd years into their career, Beach House are at a point where most artists have settled into “heritage” status at best or rehash at worst. But with “Once Twice Melody,” they’ve defied those and many other odds, creating an album that is unmistakably them, and at first blush not that different from their previous work, but one that gradually unveils more and more detail, like intricate painting viewed from different perspectives.