Cassie certainly doesn’t have the best voice in circa-2013 R&B, but she might have the coolest one: An icily direct and eerily composed sing-speak that carries volumes of insinuation with every precise enunciation. And on her mixtape RockaByeBaby, her first full-length in seven years, she knows just how to use that voice, hovering above gleaming electro-blips or snaking its way through tinkly minimal club music. RockaByeBaby has A-list guests — Rick Ross, Wiz Khalifa, Meek Mill — but they all disappear completely into Cassie’s chilly house-of-mirrors style. “I make music to numb your brain,” Cassie purrs on “Numb,” and she succeeds like no R&B singer since Aaliyah. –Tom [LISTEN]