A hallmark aspect of The Sweet Old Souls is their Carter-style harmonies, which intertwine over an old Harmony Arch-Top Guitar and an even older Martin Soprano Ukulele. Notably, both Susanna and James met as fiddle players, and each of them pick up the fiddle throughout the set as well. In this fashion, the two sweethearts play 19th century cowboy songs, 1920s-50s country and jazz, and even a few traditional Klezmer and fiddle tunes. The music is sweet, the songs are old, and the souls of the players are timeless.