The sounds I hear in the beginning are chimes so I drew the firework looking symbols to represent that. Then it slowly eases to more instruments like the circles. The circles represent the main rhythm while the other lines represent the xylophone. The long lines on the side are the computer-generated sound and long part is the violin and electric piano. You also hear a triangle with the violin which is represented by the stars. The vocal is shown through the curvy lines and the triangle is the guitar. And finally, the new instrument at the end is shown through the spiral.
The way I drew it was to be moved slowly from the top left corner down the page and back up. The observation shows how I tend to focus more on the tiny chimes on the side and the slow repeated generated sound and tend to forget the guitar is there. You can also see that the beginning of the song intentionally starts out quiet and gets busy before ending quietly too.