Lizzo's "Juice" drips so much sauce. Charly Bliss channels existential anxiety into synth-pop catharsis. Mdou Moctor's guitar will set you in a trance. There's no one sound to a year, but public radio writers across the country do set their ears to the most essential music. At the year's midway point, we asked them, as we did with albums: What is your favorite song of 2019 so far?