Probably a lot of practice. There's another video on RU-vid of them singing this same song in Mexico 2016, and they sounded awful. Glad the seemed to have cleared up what ever the problem was.
@@charlesajones77 They comeback to Mexico in 2018 touring with Mike Portnoy's Shattered Fortress and they already practice the vocal harmonies. It was a great show, also at the end of the piano/bass solo they put on a phrase that is know in jazz as "The Lick". Great detail, btw
