Waves represent the ups and downs of life. It shows what is experienced in life, and what emotions one goes through while going through their life. Taller and rougher waves a show frustration and negative feelings while the shorter and gentler ones show calmness and happiness. Music can convey many emotions to explain any idea and emotion for any audience which is similar to a wave.
Rainbows represent togetherness. It symbolizes peace and people being unified. The image of a rainbow shows beauty, and people being brought together is beautiful. Rainbows relate to music because of both bringing people together. The peace and togetherness that rainbows seem to symbolize relate to how music also brings the same.
Music is an outlet to express freedom. One can use music as a way to communicate in a lyrical way. It's freeing just knowing that one can tell a story or explain their feelings just through sounds and be able to create a song that anyone can listen to since music has no language barriers. To understand the very basics of a song, listening to how the beat and rhythm is enough to tell enough of a story and the theme of a song by just feeling it.