Was playing around with FM synthesis today to kind of back up my efforts to study music theory, and I got kind of confused about the relationship between fm ratios and notes / scales.
I used a sine wave operator (ratio of 1.0000) as the root note and stacked four more sine wave operators at the 3rd (ratio 1.2599), 5th (ratio 1.4983), 7th (ratio 1.8877), and 12th intervals (ratio 2.0000). The result was fine, everything sounded clean as expected. Then I imported a midi file with a few harmonies of a guitar track I was noodling around with and tried playing it with the above FM setup and it sounded pretty bad.
The first harmony were the notes F#5 / A5, both played at the same time like a two note chord I suppose you could say. When the notes are played together using just the root operator (1.0000) they sound fine. When they are played together and the 3rd, 5th, 7th, and 12th intervals get introduced they sound dissonant. However when the notes are played in isolation with the 3, 5, 7, & 12 intervals they sound fine again.
My music theory knowledge is pretty limited and I’m trying to understand why this is? Is it because while F#5 and A5 sound good together with just the root operator, their individual harmonies on 3, 5 , 7, & 12 do not and so clash causing dissonance?
If this is right then how do you use FM synthesis to create sounds that can be played using chords without clashing harmonics? Or is FM really just for creating big thick sounds with harmonics that are played using only single notes?