The magical angelic background sounds heard at the beginning and throughout the clip are actually the harp being played by the wind.
Harp in the Wind is a musical experience in which the wind plays on the harp, thereby making a beautiful song of the wind. The beautiful heavenly sound you hear in the background the whole song is the wind playing the harp. It's not a synthesizer! The harp is tuned to a musical pentatonic scale, which is a special tuning that every single note sounds musical with each other.