Did Clooney actually sing in O Brother?

One of biggest hits from the film, I Am a Man of Constant Sorrow, sung by the fictional Soggy Bottom Boys, which included Clooney, Blake-Nelson, and Turturro, does not include Clooney’s voice. It was actually bluegrass musician Dan Tyminski.

Who are the sirens singing in O Brother, Where Art Thou?

Mia Tate, Musetta Vander, and Christy Taylor as the three “sirens”. Their singing voices are dubbed by Emmylou Harris, Alison Krauss, and Gillian Welch.