Not talking about features (sequencer, voice count, effects, etc.), this is strictly about the quality / characteristics of the sounds produced by these synthesizers, and other recent hardware synths, like preenFM, Akemie’s Castle etc. My impression of the Volca FM is that it’s a bit more rough, dirty, and full-bodied / pronounced, whereas the Digitone sounds more polished, less rough around the edges, more refined. Maybe I haven’t dug deep enough yet, but the Digitone feels somewhat tame in comparison to other synthesizers (mostly analog) that I’m familiar with. Of course, it can make some nasty, raw, even abrasive sounds… I’m just curious about others’ impressions of it. I’ve heard some demos of the Volca FM which made it sound heavy, woody, very present, etc. – a pronounced rawness / dirtiness to it–but also lush, and slight / dainty, even. Any thoughts are welcome 
The Volca FM is wild and fun but I’m not too big on the sound. To me every patch had a sort of tinny hollow quality that couldn’t be programmed out. DN sound seems much better tbh.
You can import from many, many (many) patches/sysex files to the Volca using free software like Dexed. There is no shortage of them. So I assume there is no limit to its sound quality.
I’d like to get a Digitone, but am keeping my Volca FM. Those MIDI tracks on the Digitone were meant to be used with something after all.
Some DX7 patches by Ryuichi Sakamoto, Suzanne Ciani, etc. can be found here - it’ll be fun trying these on the Volca FM
http://bobbyblues.recup.ch/yamaha_dx7/dx7_soundbanks.html
Brian Eno patches here - his quote about FM vs. samplers is more relevant than ever
Maybe here? Sorry I forgot the Bobby Blues site is mostly just a collection of patch library names to help us sort out which sysex files to download
I was never personally satisfied with the Volca FM sound. The output stage didn’t sound like a DX IMHO. Exhibited similar sonic qualities as the Yamaha reface DX ie. too stiff and controlled, not hazy/smeary enough. Sounds more like a VST somehow…
The DN doesn’t sound like a DX either, but with the filters onboard I can compensate and generally find the sounds to be quite usable.
My fave FM sound is still the early Yamaha DX’s, with the PreenFM2 as a close second. Pretty much any FM synth can do abrasive but only the og Yammys have this mellow, smooth sound… Which I guess would be ”muffled/dark” by todays standards.
I’d agree with @Anfim, I don’t think the sound quality is all that great. I don’t have a DX7, but if you compare it with Dexed, for example, Dexed has a much fuller, more polished sound to my ears (it’s also more playable as it supports keyboard velocity and has more polyphony, but that’s another matter).
What I do like, though, is that some patches I’ve found online that I import from Dexed onto the Volca FM have a sort of low-fi gritty quality and sound much more noisy than they no on Dexed, which I’m guessing is because the sysex is actually from another Yamaha FM synth, not the DX7, and so not fully compatible with the Volca FM (which relates back to @bruin’s point about the rawness/dirtiness) . You’d think that would be a bad thing, but for very specific applications I really like this aspect, which is why I’ll probably keep my Volca FM.
I am very interested in the DN though!
I can get pretty agressive sounds from DN.
In this regard, track or master distorsions are really good.
Digitone feels high definition to me.
The only aspect one can regret is that it is focused on « musical » FM whereas most of FM soundscape is about inharmonics and such.
PreenFM for instance makes it possible to forget ratios and venture into the wild…
But I like the DN like this anyway.
Makes me think I should sell the Volca FM now 
The internal sampling rate of 96kHz might contribute to this ”hires” feeling.
Volca FM added to Digitone gives your 3 more voices of polyphony, plus extra (little) knobs and stuff for manipulating those voice; for the cost of one Digitone MIDI track.
Yep, might try to do that before, indeed 
I would be interested regarding ease of sound editing, patch creation also in comparison with the Reface Dx.
I guess, the digitone is most hands on. Can anyone compare them? Digitone, Volca, Reface?
I would reckon the best, in regards to capability, would be the PreenFM2
Simplified/quicker- Elektron
Cheaper- volca
I reckon the reface would have the more classic sound and also is the only one that contains a proper keyboard
Though I’ve only played with the Digitone outbof all of them
With fm hardware synths, I always have doubts if they are worth it, from a editing fun point of view. Not with the digitone, cause it seems to have a simplified hands on interface, but it’s at least double the price than the others.
But for the other 3 mentioned, I always ask myself if I would have more fun with them creating patches, compared to Ipad fm synths like phasemaker where you can control most parameters quite easily (also if they are superior in sound)
Akemie’s Castle looks pretty fun to use / hands-on… with those old Yamaha chips under the hood it sounds quite pleasing (raw, immediate, physical), having listened to demos by Mylar Melodies and DivKid on youtube. The only complications are that you’ll need a Eurorack “skiff” (??) to use it, and the price (nearly that of a Digitone) - but it sounds excellent, and the interface is quite direct.
Yes, it sounds excellent and seems a lot of fun. Akemie’s Taiko as well
I’m currently looking to incorporate more FM sounds into my music and have been wondering this very thing. I’m almost ready to just say screw it and keep using my folder full of old classic FM samples.
But, while putting together a (yet another…) tiny OTB setup, I want something in hardware. Coming from using FM samples, and seeing as how many great DX-7 patches are out there already, I feel like FM, for me, would be mainly about finding great presets and then slightly tweaking. I have zero interest in programming FM from scratch.
I’m leaning towards the Volca FM as it’s cheap, still has a few hands-on controls to vary the patch sound, and loads old DX-7 patches, and imho sounds more alive than the Digitone.
Real FM synth vs. FM sample player, round 25…
Cheap way to settle this:
1… Set up your FM sample player for use with MIDI controller
2. Get Dexed (free DX7 softsynth) and set it up for MIDI controller
3. Get velocity-sensitive MIDI controller (pad or keyboard)
4. Play FM Player and Dexed with your controller, one at a time and listen to how each responds to your playing velocity.
Don’t just use a step sequencer or other automated thing to compare FM sample player and FM synth. Really play manually to hear for yourself if there really is a difference in response, sonic behavior, etc.
That’s the most fun part of fm for me
Frequency of surprising happy accidents is much higher compared to subtractive synthesis