I had a music teacher once who said that he was interested in the borderline between timbre and harmony. I’ve always remembered this, and I think it’s a really cool observation.
He was classically trained, and so was coming from a tradition that split the components of music like this: rhythm, melody, harmony, timbre. The first two are what you’d think they would be, the third (harmony) is also what you would think (i.e. notes played at the same time, or chords), and the fourth (timbre) is about what the actual instruments sound like (clarinet, piccolo, electric bass).
The reason that timbre and harmony overlap is even single notes are complicated things, and have overtones. If I play a note on the piano, the actual wave generated in the air is a combination of that note, plus the note at twice the frequency (i.e. one octave up), plus [etc, with dimishing volume]. The way your ear decodes this is as a single (rich) tone, rather than as a bunch of notes at once. Part of what makes different instruments sound different is the loudness profile of their overtones (flutes have almost none, pianos have more, brass instruments have a particular prominent pattern).
But if we know that ears work this way, can we spoof them? Since flute tones basically have no overtones, how about if we organize a conspiracy of flautists to try to imitate the piano: all at once, one of them will play a note, and at the same time another will play the note an octave above somewhat more softly, and another one a fifth above that … This essentially works (if you ignore differences in attack/decay). Electronic music allows you to