Feedback FM
Hello everyone. I'm reading Curtis Road's the computer music tutorial and in the Feedback Frequency Modulation part of the book I saw the figures below. I guess I made first one but I got confused while doing the second and third. Can someone solve this tables in Max/Msp patch and share?
Esteban, examples #2 and #3 use the same techniques as #1. Why don't you Copy-Compress what you have for patch #1 and paste here? That could be a good conversation starter.
For feedback FM you'll probably want the feedback loops to be single-sample delay, which means you probably want to use gen~ and [history] objects in the feedback paths.
Notice that the diagram caption describes "x" as a "phase increment" for a "sine lookup table".
A sine lookup table in gen~ is [cycle @index phase] (indexed as unipolar phase from 0 to 1), or you can compute it directly using [sin] (indexed in radians from 0 to twopi).
Using "phase increment" also means your frequency parameters are not in Hz, but in phase change per sample. You can convert Hz to unipolar phase for [cycle @index phase] using [/ samplerate] or to radians for [sin] using [* twopi/samplerate].
There's more subtleties to feedback FM (and feedback Phase Modulation). I highly recommend adding some kind of filter in the feedback path -- even the Yamaha DX algorithms used a very crude averaging FIR filter on feedback paths, but things can get a lot more fun and controllable with better filters.
(PS. Honest plug: There's a whole chapter about FM/PM etc. including several feedback variants in this book: https://cycling74.com/books/go) :-)
thank you for all answers. what about bulding feedback fm without gen~ and least feedback time using send~/receive~ pair?
I added patch below that it explaine what I want to explaine. If I made wrong, building all three type of feedback FM it will worth for me and for who want to learn with easiest way.
Using a send~ / receive~ pair as in your patch introduces a signal vector of latency. The sonic result will depend on your Signal Vector Size (and options depend on your audio interface).
[gen~] and the [history] object allow you a single sample of "latency" in the feedback loop.
Thank you so much Jean-Francois and Graham. When I do I will share it here.