According to Wikipedia:
Caoimhín Ó Raghallaigh is a fiddler, born in Dublin in 1979. He is known for developing a drone-based fiddle style heavily influenced by the uilleann pipes and the music of Sliabh Luachra.
Caoimhín plays an old trade German fiddle, which he keeps tuned down four or five semitones below concert pitch, a hardanger fiddle, a 5-string viola made by David Rivinus as well as a number of other fiddles. He uses many crosstunings or scordatura, and often plays with a baroque bow made by Michel Jamonneau. Caoimhín also plays tin whistle, flute and uilleann pipes.
What I heard is the sound behind the melody. There was something we used to call the music of the spheres and the underlying whatever it is in O Raghallaigh’s music reminds me of that. Don’t you think?