rainwarrior wrote:I don't know of any textbook that teaches how to make good FM instrument patches. Finding a well balanced tone is usually very sensitive to small changes, a brief peak of serenity in a sea of BLAARRP. Hard to generalize.
That's why you start making the right tone without dynamics, ADSR set to max attack and infinite sustain. Then dynamics part is out the equation and you can entirely focus on the serenity part or the BLAARRP and anything inbetween. If modulation grows too high you're gonna get those harsh sounds, so you scale back modulation factor accordingly so that such state isn't reached. TL parameter is the peak level the operator can reach.
If you see regularly placed harmonics then you use one op modulating the other to create them, if you see regularly placed harmonics in the sequence you add one more op to the mix for that, if things are offset and not following exact same sequence but are still in a sequence you need another frequency ratio for them. If there's some random non repeating harmonics you're very much forced to waste an operator on those, non modulated ops that is.
You'll want to make the computer record its output and see a spectrogram taken realtime how the modulation changes harmonic structure. The rules between TL, MUL and other parameters are very straightforward, you just got to ignore that dynamics exist first.
Once tonality is set you can then work on dynamics. Start with output ops, and then touch the modulators. Changing ADSR parameters of the modulators will affect tonal qualities, the lower the modulation factor gets (operator level) the more smoother (sine like) the sound gets, which mimics how the higher energy harmonics fade away first when a note is decaying. Parameters like Key Scale will speed up the envelope has notes go higher, something that real instruments experience also, high keys on piano will never have a long sustain no matter how hard you hit them. There's also an LFO and detune parameters which can be used to create beat frequencies or other things to make a sound more dynamic, unfortunately speed of LFO is global.
And you'll want to keep your eyes on a spectrogram.
I do think using FM to recreate classic instruments is wasting away the potential, you can do so much more, things that don't exist yet. Having said that, one 4op FM channel can do very much 1:1 or nearly that approximation of *a string* of any classic instrument, but you only have 6 or 8 channels on the popular chips so things like pianos are gonna be very ineffective because their characteristic sound comes from the fact that most notes have 2 or 3 strings used, and their tuning isn't exact, using half or 1/3rd of the chip for one note is not great for making a full composition however... You can do a very nice acoustic guitar though, but a lot of effort will have to go into adding the human playback imperfections such as finger sliding and fret noises.