It was after "#Selfie" became a Top 40 novelty hit that The Chainsmokers began aiming for a more durably successful sound. Their follow-up, "Kanye" was a collaboration with the L.A. dream-pop duo sirenXX that captures the sadness of regular people dazzled by celebrities and disappointed that they can't join their ranks. (The video showed a Latina hotel maid enjoying a Cinderella night, then returning to her daughter and partner in their humble Los Angeles home.) It set a tone. Nearly every subsequent Chainsmokers success features women vocalists whose melancholic observations and confessions offset the busy buzziness of the beat-driven mix. Most are little known; the DJs found them via music blogs or the aggregator Hype Machine. (Let's hope they gain more recognition than did some earlier women whose voices were featured on major dance hits, like Martha Wash, who had to go to court to be recognized.) There's "Roses," a seduction narrative turned off-kilter by the contributions of singer-songwriter Elizabeth Mencel, who calls herself ROZES; the searching "Inside Out," featuring the trilling voice of the Swedish artist Charlee; "New York City," whose singer, Victoria Zaro, has a voice like a teardrop; and "Don't Let Me Down," the closest thing the duo has to a house music-style soul epiphany, with the plaintive stylings of the teenager Daya lifting it aloft.