worldbuilding thought
thinking of what music by alien species would be like and honestly, I figure the main differences from what you find here on Earth would be more in the rhythmical and instrumentation (or if electronic, sound design) department than harmony per se
there's only so many combinations of chords you can smash together that'll sound right even if you consider differences in the theory behind it all and plenty of music here on Earth doesn't use chords, period
worldbuilding thought
i mean sure there's microtonal stuff & all, & to expect everything made by people elsewhere in the universe would be in 12TET would be a joke, but no matter how many keys you add to the keyboard, there's only gonna be so many combinations of intervals that sound nice together
of course which ones prove the most popular and for what is a whole other thing, but given how much the 7½ billion of us have collectively messed with that ourselves, probably nothing new under the sun
worldbuilding thought
@Thaminga Consider: different ranges of sensitivity. Music with infrabass or ultratreble, with parts that are simply inaudible to human ears.
I will leave composing such music a an exercise for you. I'm sure it's quite simple to do. :)
Consider: multiple atmospheric vibration sensors, which respond to different frequencies. "oh geez I really hear that in my fronds, wow" And brains that are quite happy to track different harmonies for each set of sensors. Maybe some rough rules about what kinds of overlapping harmonies that sound terrible to human ears but work well to theirs - some combinations of harmonies in (ears1) and (ears2) would come off as grating, some would sound great.
I'm sure composing this would be quite simple as well. :)
worldbuilding thought
@anthracite oooh yes, I approve of these ideas 💙
worldbuilding thought
@Thaminga you could even get really wild and do something like "they have magnetic field sensors that feed into their brain via the same part that processes sound vibrations", music then gets to consider the relationship to the planet's magnetic field, there might be instruments that are solely about waving magnets around to produce nothing humans would sense at all, different cultures on this world might have different ideas about how a performer and audience should be oriented relative to the prevailing magnetic field that might make performing a foreign piece nigh-impossible in a Serious Concert Hall, and makes things really interesting for musicians who leave the planet.
(Inspiration: I recently read that birds apparently process their Magnetic Sense through their visual cortex, and essentially have a completely different "color" overlaid over everything they see. Feel free to think of some other thing that we can only sense with the help of machines.)
Again, I'm quite sure this is completely trivial to take account of when using Earth musical equipment to compose a simulacrum of it. Completely.
worldbuilding thought
@anthracite oh yeah! I was just thinking in the sense of music as we know it; ie, using actual sound and all. obviously you'd open way, way more possibilities if you start looking at equivalents for different senses!
worldbuilding thought
@Thaminga i'm not even stoned :)