I think of music as a way to express emotion. We all know what a happy song is, and we’ve all heard music that made us feel very sad, nervous, calm, energetic or even nostalgic.
Now, I have no idea how we first came to enjoy music from instruments. But it doesn’t seem farfetched to asume that we started out chanting or otherwise vocalizing our feelings, then began singing very simple songs, and went from there. In that sense, it’s not really that music is the source of emotions. Rather, music is a translation of our feelings that we understand instinctively. We might even share this language with some other animals. For example, studies by Patricia McConnell reveal that people all over the world use rapid, short repetitions of sounds to speed animals up, and a long, drawn-out note to slow them down (“woooooah”). Music that makes us happy tends to be faster, with distinct beats. Sad music is often slow. And the Kalimba music that relaxes my dogs makes me feel calm, too.
It does of course matter what you personally associate with the music you’re listening to. For example, if you grew up much earlier or much later than I did, the tune I linked as “nostalgic” above will not be very special to you. There are a couple of songs that sound “happy”, but that make me sad because they were played at my great uncle’s funeral. And while my husband likes gothic chants because he grew up hearing them, they sound threatening to me. Music has a strong cultural element, but certain elements are universal.
You might like to read this article: https://news.harvard.edu/gazette/story/2019/11/new-harvard-study-establishes-music-is-universal/.