So far we have had the basics, now it can start getting quite complex in the way the oscillators are set up. If we look at the chart below this shows some of the possibilities for how the oscillators can be routed. And this is without feedback loops! Just remember that for each oscillator (except the first modulator(s) in the chain you’re going to want to control the level of modulation fed to the next oscillator in the chain, whether you use the same modulation control source for each level control, or whether you control each one individually is entirely your choice.
Going from left to right the last oscillator in the chain is always the carrier, all the others are modulators. The carrier oscillator is always the audio output oscillator. No audio is used from the modulators except for modulating other oscillators.
Feedback and routing possibilities:
Again the possibilities for how you route the feedback are endless…
And as you can see things can quickly become very, very complex in terms of signal routing, especially if you want the VST’s user to be able to change modulation and feedback routing for programming your synthesizer.
Do I need a VCF in my FM Synthesizer?
It’s a matter of personal taste. An FM Synth in theory shouldn’t need one as it can do all that a subtractive synth can do…and more. However some like the sound of a Hybrid (FM + Subtractive synthesizer, so feel free to add a filter into the output chain. Though if you want to you could add the usual Subtractive synth modules alongside the FM synth section.
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