FM, TZFM, Wave Folders and Eurorack Modules (2025 Edition)

[ghettosynth]

Let's talk about FM in Eurorack and what are some of the options, analog and digital, in 2025.

I have a number of interesting from an FM POV oscillators, but none of them do TZFM. I'm debating between getting a complex oscillator with TZFM, or, just buying TZFM capable oscillators and a separate wave folder.

[ghettosynth]

I like Klavis stuff. This does not seem feature reach in terms of FM modulation, but, it is flexible.

[ghettosynth]

I also like ALM stuff a lot. This is close to $300, for a single oscillator (used) but it's analog.

[wintoid]

The Schlappi Three Body turned out to be everything I wanted.

[ghettosynth]

The Schlappi Three Body turned out to be everything I wanted.

Ah, yes. I read about this recently, it's based on FPGAs IIRC. As far as digital osccilators go it seems capable. No integrated wavefolders, but PM and FM and three oscillators.

I like this person's demos.

[foosnark]

I like Klavis stuff. This does not seem feature reach in terms of FM modulation, but, it is flexible.

I had the first version of the Twin Waves and really didn't think much of its FM. Overall it just seemed a little vanilla to me somehow. I know shortly after I sold mine there was a firmware update, and I think the current one also has updated hardware. So I'm not judging the current iteration too harshly.

My rack is full of FM-based and FM-capable stuff...

Akemie's Castle: uses the Yamaha OPL3 (YMF262) chip that was used in Sound Blaster Pro and AdLib Gold sound cards. To keep the interface more immediate and not be *too* enormous of a panel, you don't get the full capabilities of the chip, but there are two 4-op oscillators with one having a 5-voice chord mode.

It sounds grungy in a perfect way, and the modulation is pretty steppy because of 5-bit level registers on the chip. I love it, and every time I've reevaluated to decide whether to use the HP for something else, I've immediately thought "no, I have to keep this."

...

RYK Algo: the clean and shiny and more flexible companion to Akemie's dirt. It's high resolution, you don't get that sort of noisy hiss with some ratios/depths like a lot of FM. I got this to replace a Shapeshifter because of how I usually wound up using Shapeshifter. It sounds fantastic, has some algorithms that the original DX synths didn't, and offers ratio tuning, free tuning and fixed tuning of operators plus fold and warp features, detuning, stereo (panning of carriers) and chorus. There's a handy master FM knob and CV that acts as a multiplier for the individual levels.

It does have some really bizarre/unfortunate design decisions; despite these it's still a wonderful module and gets a lot of use.

- the panel is sexy but reading the algorithm from the dotted LED diagrams takes some getting used to, and the diagonal layout is kind of weird.
- the output is a stereo TRS jack. It does ship with a splitter cable, but it's f**king annoying. I got a different cable with a low-profile 90-degree TRS plug, routed that through a ventilated blank next to the module, and have that plugged into my Mazzatron Mult & Passthru so I don't have to worry about it.
- there's no master tuning knob, just octave select. To work around this you can set one of the CV inputs to FM and use an external utility to transpose everything.

...

MI Rings: Its FM mode (tap the mode button so it's green, then hold it down for a few seconds so it blinks) is the same one that wound up in Plaits. Not a lot of complexity or sophistication but it has its uses.

...

Noise Engineering Toros Iteritas Alia: A unique and clever take on FM, it has 3 operators and three algorithms that are all circular, and "Blendex" parameters that crossfade from carrier to modulator so that all operators are always having some audible influence. The FM is a little bit dirty, and as with most Noise Eng stuff it can get super aggressive but doesn't necessarily have to. In the area of FM, Noise Engineering also offers Debel and Incus, but I don't find those as interesting overall... the nice thing is you can swap the firmware freely though and try everything.

...

Make Noise Spectraphon: there is a lot more going on with Spectraphon, but just focusing on FM: first, in all modes the FM bus modulates A with B's core sine and B with A's core sine, but the modulation isn't circular (it's phase modulation like on the Yamaha DX, and the core sine is unaffected). You can have B track A's frequency or sync to A's core.

Secondly, Chaos Mode is phase modulation. Focus controls the ratio of an operator that seems to be derived from or synced to the core frequency in some unusual way I can't figure out. Partials controls the modulation depth, and Slide adds some chaotic wobble (I think to the depth since it does nothing with Partials at 0, but it may also affect frequency). Combine that with the FM bus, and being able to detune the even/odd outputs, and you can have a lot going on. Frankly, I would still love the module if Chaos Mode is all it had.

...

Xaoc Odessa: again, not primarily an FM module -- but it has both expo FM and TZFM inputs. As an FPGA-based module, it has very high resolution and internal sample rate so it handles FM like a champ, and the modulation depth can be really strong. This typically works best with only a few partials, because it doesn't scale the depth down for higher partials -- but there are some cases where it sounds wild and great with a strong depth and high tension. It seems hyper sensitive to having a clean, DC-free modulation signal though.

...

Whimsical Raps/Mannequins Just Friends: unlike its cousin Tides, it does TZFM, and it does it very well. You can use an external modulation source, or you can plug something into the Run jack to use internal modulation oscillators (with Run determining ratio, and each of the 6 outputs gets its own modulator so they have consistent ratios). Negative FM depth affects outputs 2-6 but not 1, so you can use it as a modulator or just keep an un-FMd fundamental in the mix. With all the waveshaping available and the Mix output, it's quite flexible.

...

Mutable Instruments Blades: yes, it's a dual filter, not a VCO. But it self-oscillates well, and there's CV control to sweep from LP to BP to HP -- since this causes phase shift, modulating them at audio rate is phase modulation. The available depth for clean PM is limited, but it goes to a sort of phase distortion after that so it's still useful. And you can have the two sides cross-modulate without getting chaotic.

...

I've had many others in the past. Hertz Donut mk2 and mk3, Shapeshifter, Mutable Warps (it does PM with its internal oscillator enabled) and Plaits, SynthTech E352 and E370. Happy Nerding FM Aid. I do kind of have an FM fetish

[wintoid]

I do kind of have an FM fetish

Sounds normal to me

[ghettosynth]

I like Klavis stuff. This does not seem feature reach in terms of FM modulation, but, it is flexible.

I had the first version of the Twin Waves and really didn't think much of its FM. Overall it just seemed a little vanilla to me somehow. I know shortly after I sold mine there was a firmware update, and I think the current one also has updated hardware. So I'm not judging the current iteration too harshly.

My rack is full of FM-based and FM-capable stuff...

Akemie's Castle: uses the Yamaha OPL3 (YMF262) chip that was used in Sound Blaster Pro and AdLib Gold sound cards. To keep the interface more immediate and not be *too* enormous of a panel, you don't get the full capabilities of the chip, but there are two 4-op oscillators with one having a 5-voice chord mode.

It sounds grungy in a perfect way, and the modulation is pretty steppy because of 5-bit level registers on the chip. I love it, and every time I've reevaluated to decide whether to use the HP for something else, I've immediately thought "no, I have to keep this."

...

RYK Algo: the clean and shiny and more flexible companion to Akemie's dirt. It's high resolution, you don't get that sort of noisy hiss with some ratios/depths like a lot of FM. I got this to replace a Shapeshifter because of how I usually wound up using Shapeshifter. It sounds fantastic, has some algorithms that the original DX synths didn't, and offers ratio tuning, free tuning and fixed tuning of operators plus fold and warp features, detuning, stereo (panning of carriers) and chorus. There's a handy master FM knob and CV that acts as a multiplier for the individual levels.

It does have some really bizarre/unfortunate design decisions; despite these it's still a wonderful module and gets a lot of use.

- the panel is sexy but reading the algorithm from the dotted LED diagrams takes some getting used to, and the diagonal layout is kind of weird.
- the output is a stereo TRS jack. It does ship with a splitter cable, but it's f**king annoying. I got a different cable with a low-profile 90-degree TRS plug, routed that through a ventilated blank next to the module, and have that plugged into my Mazzatron Mult & Passthru so I don't have to worry about it.
- there's no master tuning knob, just octave select. To work around this you can set one of the CV inputs to FM and use an external utility to transpose everything.

...

MI Rings: Its FM mode (tap the mode button so it's green, then hold it down for a few seconds so it blinks) is the same one that wound up in Plaits. Not a lot of complexity or sophistication but it has its uses.

...

Noise Engineering Toros Iteritas Alia: A unique and clever take on FM, it has 3 operators and three algorithms that are all circular, and "Blendex" parameters that crossfade from carrier to modulator so that all operators are always having some audible influence. The FM is a little bit dirty, and as with most Noise Eng stuff it can get super aggressive but doesn't necessarily have to. In the area of FM, Noise Engineering also offers Debel and Incus, but I don't find those as interesting overall... the nice thing is you can swap the firmware freely though and try everything.

...

Make Noise Spectraphon: there is a lot more going on with Spectraphon, but just focusing on FM: first, in all modes the FM bus modulates A with B's core sine and B with A's core sine, but the modulation isn't circular (it's phase modulation like on the Yamaha DX, and the core sine is unaffected). You can have B track A's frequency or sync to A's core.

Secondly, Chaos Mode is phase modulation. Focus controls the ratio of an operator that seems to be derived from or synced to the core frequency in some unusual way I can't figure out. Partials controls the modulation depth, and Slide adds some chaotic wobble (I think to the depth since it does nothing with Partials at 0, but it may also affect frequency). Combine that with the FM bus, and being able to detune the even/odd outputs, and you can have a lot going on. Frankly, I would still love the module if Chaos Mode is all it had.

...

Xaoc Odessa: again, not primarily an FM module -- but it has both expo FM and TZFM inputs. As an FPGA-based module, it has very high resolution and internal sample rate so it handles FM like a champ, and the modulation depth can be really strong. This typically works best with only a few partials, because it doesn't scale the depth down for higher partials -- but there are some cases where it sounds wild and great with a strong depth and high tension. It seems hyper sensitive to having a clean, DC-free modulation signal though.

...

Whimsical Raps/Mannequins Just Friends: unlike its cousin Tides, it does TZFM, and it does it very well. You can use an external modulation source, or you can plug something into the Run jack to use internal modulation oscillators (with Run determining ratio, and each of the 6 outputs gets its own modulator so they have consistent ratios). Negative FM depth affects outputs 2-6 but not 1, so you can use it as a modulator or just keep an un-FMd fundamental in the mix. With all the waveshaping available and the Mix output, it's quite flexible.

...

Mutable Instruments Blades: yes, it's a dual filter, not a VCO. But it self-oscillates well, and there's CV control to sweep from LP to BP to HP -- since this causes phase shift, modulating them at audio rate is phase modulation. The available depth for clean PM is limited, but it goes to a sort of phase distortion after that so it's still useful. And you can have the two sides cross-modulate without getting chaotic.

...

I've had many others in the past. Hertz Donut mk2 and mk3, Shapeshifter, Mutable Warps (it does PM with its internal oscillator enabled) and Plaits, SynthTech E352 and E370. Happy Nerding FM Aid. I do kind of have an FM fetish

Thanks, that was an excellent response. I appreciate the detail. Algo and Odessa are interesting to me, especially Odessa.

[foosnark]

Odessa's pretty great, one of those things where I just keep discovering new ways to use it, without it feeling as much to me like a random needle-in-haystack hunt for sweet spots as some things. And IMHO it sounds even better with some distortion after it.

[pdxindy]

Odessa's pretty great, one of those things where I just keep discovering new ways to use it, without it feeling as much to me like a random needle-in-haystack hunt for sweet spots as some things. And IMHO it sounds even better with some distortion after it.

Odessa -> 100 Grit