Studying FM synthesis and I can’t help wonder why they went with A, B1, B2, and C on the Digitone and not A, B, C, D? I’m sure there’s a great reason and I’d love to know!
The FM engine in Digitone is a bit weird. I think it is because they wanted to reduce the number of menu pages and knobs as much as possible and making it faster to tweak.
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But aren’t B1 and B2 separate operators? Why not just give them unique names? I’m sure there’s another reason.
They don’t have separate envelopes so they are not fully independant operators.
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Ahhh. So in essence:
Envelope A - operator A
Envelope B - operators B1 and B2
Envelope C - operator C
Yes, except that C does not have a separate envelope, but is a carrier so the amp envelope will kind of work as a envelope for this one. Acually the amp envelope will work as a envelope for C and the one of B1 and B2 that is a carrier in the chosen algorithm. Envelope B will work as a modulation envelope for the one of B1 and B2 that is a modulator in the algorithm.
C is always a Carrier,
A & B1/2 are typically modulators 
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Yes, A and B2 are mostly modulators, C and B1 are mostly carriers, depending on the algorithm.
As I say it is a bit weird, but fast to tweak when you have learned it. I have a Yamaha DX7 and use it often. It has six identical operators and I actually find it easier to understand, but it takes much more time to make the patches because of all the meny pages and very limited information in the display.
Yeah I can see from the diagrams that C is only used as a carrier. Never really noticed that before.
Still struggling to understand the B1 / B2 naming convention. Especially as most FM synths I can see have different letters for each operator.
I can understand that! The B-level knob is all time high in weird functionality, have a look at the graph in the manual that shows how it works
Cool, will do. FM synthesis is amazing, been reading about the damage done by the legacy of the DX7. So it’s great that new machines / software is being made to approach this technology in a more usable way.
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Yes, but I think the DX7 is muuuuuch easier to use than its reputation, you just have to read the manual. But I love FM, the FM/subtractive combination in Digitone opens up endless of sonic possibilities. I also love that the two LFOs can be used as envelopes for FM parameters like feedback and harmonics.
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Ok I’ll explain a bit further (was on my phone) …
C is named C simply because it’s always a Carrier, and the two modulators (which can be used as carriers in a lot of the algorithms) are named A & B1/2 for some consistency. Typically you go from top down in FM algorithms anyway, so it makes some sense to view A as the ‘first’ oscillator and C as the last - or the ‘result’ of the algorithm.
The B operators are a grouped pair and share all the controls - they are carefully mapped to give you as much flexibility as possible without interfering with the simplicity of the synth structure and concept. For example the Level of B has a particular mapping which applies the modulation level in a certain way that makes sense for the structure itself.
I tend to think of the Digitone as a 4-OP FM synth with a 3-OP control and one of the operators has a secondary tone generator for timbral complexity - almost like if you would have a wavefolder connected. This differs from typical FM synthesis in how the two grouped operators have one singular envelope.
The reasoning behind this is to provide a tweakable FM synth where you don’t need to know or bother with details as much as a more modular approach (Yamaha-style) and is, in my opinion, inherently more explorable and approachable because of it.
As for whether it’s weird or not - that depends on how you look at it. Does Yamaha’s FM concept define what an FM synth is? I don’t think so. It’s a different paradigm for sure though, and coming from a classic FM synth it is a bit alien. I find aliens pretty funky myself.
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That’s incredibly useful, I was starting to understand that B was kind of a self-contained system. So yes - 4 OP synth / 3 OP control is a great way of looking at it.
I can also see what you mean about FM / DX7. There is no set way, and A, B1, B2, C is Elektron’s own approach, which as you say offers a fairly unique level of expression and speed.
Nice explanation Ess, but still you could have “simply” labelled the operators A, B, C and D. 
Maybe it was part of the design approach to make ‘C’ stand for ‘Carrier’ seeing as C is always the carrier?!
But yeah - that’s what I was thinking! Why not make D the one that’s always the carrier? With B and C sharing the same envelope, etc.
Or maybe they just wanted to be quirky
The combined B operator is really the only thing I dislike about the digitone. I wish they had separate envelopes. On the other hand you can get some really weird sounds with the two operators being modulated in opposite directions like it is set up.