One of the things I have thought about is identifying a key difference between classical music and pop music. I know that the two genres generally sound very different. There is also a tremendous amount of variety in both genres. But I tried to pin down the one difference that holds true across almost all pop songs and almost all classical music pieces.
There seem to be some obvious answers such as a steady tempo. But there are many classical pieces with a steady tempo. You might say that it is the instrumentation. But there are pop songs for voice and piano. You might say complexity. But there are complex pop songs and classical music pieces with very simple melodies and textures. The differences I’ve mentioned so far seem to have all kinds of exceptions.
But there is one difference which seems more consistent. I am referring to repetition. In both genres you have a meter which repeats. But in pop music there is a different balance between new material and repetition. There is usually more repetition. There is a drum track. There is a kind of melodic or harmonic groove that can last throughout large sections of a song or the entire song. In classical music something is usually only repeated three times, then the composer writes different material. The overall balance is more towards new material and less towards repetition.
Maybe there are some other consistent differences that I am missing.