I'd be interested to see the results of this study if the participants were exposed to ambient drone music, such as sounds of a didgeridoo or a Steve Roach piece, that music often consists of long drawn out tones that don't fluctuate frequently and often lack a "melody". For me, it puts me a deep trance like state of mind that is very calm and peaceful. Humming along to the long tones also feels good, it's like your body resonates with the music.