Have been doing some research on FM modulation lately, as I am trying to build the circuit of an Elektron Digitone in Pure Data. Just for the fun of it. I love these bigger project, to see how close one can come with freeware But they always end up being a bit over the top for Axoloti so I end up in PD every time.
Been trying to find out, which is the best way of doing these things, like for example fm and fm feedback. It seems the use of FM/PM quickly get a bit blurry as some synth use one thing and call it the other and vice versa.
Here is some papers, which were suggested by a guy in the PD forums, whom is very knowledgable.
And he actually talked about trying to avoid using HP filters in fm, cause it could cause small burst in a feedback FM situation if the amount was too high. But yeah it might not be the same, cause we are not talking about FM feedback here. He mentioned in context of FM feedback.
Anyway, he as referring to this patent here, when he mentioned it, figure 7 is the burst and figure 8 is the filter, he said:
He also talked about doing oversampling to prevent some of those mishabs that sometimes happens in FM synthesis.