I am listening to a music compilation titled Total War: Rome 2 OST - Campaign Compilation. This is composed by Richard Beddow and performed either by the Prague Philharmonic or Slovak National Orchestra, as per the details in the video description. The track starting at 3:58 mins has a humming female voice alongside some stringed and woodwind instruments.
Is there a genre of this type of music (containing such humming vocals), and if so, what is it called?