Hallelujah mixes a single-song deep dive and a standard music doc. Even if you’ve never heard of Leonard Cohen, you’ve almost certainly heard his song “Hallelujah.” Maybe you’ve heard the version by Jeff Buckley, or John Cale, or Rufus Wainwright, or a contestant on a TV singing competition. Maybe you don’t even realize that you’ve heard it, because it was playing at the grocery store or in a movie or TV show. It’s one of those songs that’s become so ubiquitous that it’s transitioned into background noise.