The math is just Asin(at+Bsin(bt+...))+Csin(ct+...), where you can slowly play with A, a, B, b, ... but to get a good musical intuition try this tutorial for th

The math is just Asin(at+Bsin(bt+...))+Csin(ct+...), where you can slowly play with A, a, B, b, ... but to get a good musical intuition try this tutorial for the Yamaha Reface DX (a modern incarnation of this algorithm, identical to the DX7 except they replaced the last two operators with a feedback unit per op instead of just one): https://www.yamahasynth.com/synths/basics-of-fm-synthesis https://www.yamahasynth.com/synths/basics-of-fm-synthesis