Understanding Through Zero FM

I don’t quite understand through zero fm yet. Does anybody have a good explanation / tutorial they recommend?

Just moved this topic here so it doesn’t detract from the firmware thread too much as this is a huge area and it easily justifies it’s own thread.

You could do a lot worse than read the SoS synth secrets series, see part 12:



A little sound where i have compare thru zero fm analogic with zeroscillator and the one with the ER301.
Little quiz, which is the ER301, first or second one ?


Either could be the ER-301, they both sound good to me in different ways, but I can’t really play because I have no idea on the fm analogic.

Pure guess… I’d go for the first one being the ER-301 :slight_smile:

Agree, both sound good. I’ll guess the second one is ER-301.

2nd is the 301 I think. Sounds great, I need to update now

Kel is victorious, the ER301 is the first one.


Yay - I won something :smiley:

I can’t really take any credit for it though, it was just a guess, perhaps a little bit of a hunch because it sounded smoother, but nothing I could really quantify.

Holy crap - just looked up the zeroscilltor - 1100+ USD :open_mouth:

Let it never be said again that the ER-301 is not outstanding value for money - what a great comparison - thanks for doing that!


I think this is a good one, if you prefer video format.

Very nice video Joe.
It only explain the difference between exp and linear fm, now we have to find one wich explain the difference between linear fm and thru zero linear fm.

I must admit I am uncertain where the opening up of TZFM is evident in the modules which Brian mentioned. I’m aware that I have been producing FM synthesis (although unknowingly prior to reading the SOS article and watching the video!) but I’m unsure of how there is something different in the Ladder Filter, Sine Osc, Aliasing Saw, and Aliasing Triangle. Is f0 on the frequency of these units indicative of the change here?

I believe you’ll have to modulate the hertz control, that is, the f0 control. that gives you linear thru-zero FM. modulating the V/Oct control would give exponential FM. (EDIT: previously I said exponential thru-zero FM, which is not the case, of course!)

Thanks for this, I love to hear demos and comparisons without specific musical context, really inspiring.

Yes, that’s what I thought, but just looking at the modulation indicators movement when feeding in a modulating triangle wave, it looks to be still exponential i.e. the modulation indicator of f0 drops far lower beneath the bias setting than it does on the upward movement.

Sorry if my language not precise or technically correct, but does that make sense?

(actually on reflection it appears to be the inverse of that which was described in the video Joe offered)

Rest assured that f0 modulation is linear. Only the fader display itself is scaled exponentially, because otherwise you would not see any modulation.

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There is no such thing as thru-zero exponential FM because the exponential function is always positive.

Please allow me to recall a previous post I made that clarifies:


Thanks Brian,

But now, unlike in your diagram below, the f0 function is able to modulated? (and that’s the unlocking part?)


See, I’m learnin’ day by day! :slight_smile:

So in that instance where I have a triangle LFO modulating f0 and on the lower scope it shows as equidistant about the midline yet on the f0 modulation the bulk of the modulation occurs beneath the the bias amount, very little above it, what’s going on there? Do I need to offset or attenuate that modulation signal coming in?

Only the fader display is scaled exponentially. That is why the modulation looks lopsided. A linear display of frequency is almost useless. Can you see why? Imagine if the fader tried to display 0Hz to 12000Hz in a linear fashion? Where would 300Hz be on the fader? How big would a modulation index have to be before you can see it?