So what exactly (if anything) can analogue filters do that digital definitely cannot? Besides the whole "warmth" thing. Anything? - or is it all hype?

Analogue filters seems to be the most important (or even mandatory?) part of a hybrid synth, where as oscillators doesn't make as much of an impact? Could analogue filters on digital oscillators be better somehow than analogue on analogue?

Does filtering wavetables versus waveforms make a difference?

Osc are more important than filters IMO.
Most notably if things like FM, Osc Sync, Ring Mod, etc. are coming into play, analogue osc can yield better results (particularly at higher registers). At 192khz sample rates and up maybe such will start becoming less of an issue, but as stands that doesn't tend to be the norm and subsequently I still find it to still be a bit of an issue generally speaking (not an overly huge one, but it's there).
Granted, I find Osc sources and their potentials more important than filters in the greater general. With the right Osc, one won't even need filters.

Not quite sure why filters are brought up so much more frequently than Osc.

Have noticed that there does seem to be more of a focus on Osc and their potentials coming up today though. Notably Wavetables (of the Palm sort) and otherwise continuously morphable waveshapes seem to be quite the rage, but it's coming up in other ways as well.
Digital Osc tend to grant considerably more overall flexibility than analogue Osc in the area of waveshape generation and (specified controlled) manipulation, so not sure I'd say analogue filters on digital osc sound better as much as digital osc tend to grant more flexibility in what sort of controllable waves can be done with them (in practical fashion) than analogue Osc.

It'd be nice to see areas like Zplane filters and other areas analogue filtering has a trickier time with explored more.... while that also seems to be a "wee" bit on the rise, it's still something rarely explored in general. Not sure why really.

The special thing with analogue is mostly that "perfect (analogue) fidelity" isn't having to be chased down (IMO), one is just there. Beyond that, not really sure what's overly special about it.

Both analog oscillators and analog filters are important. After all filters can only work with what they receive (well ok - there's self oscillation too).

Digital waveforms sampled from analog stuff may work well up to a point where the difference between them and analog oscillators stops being noticeable - if there's enough sampled variation of those... for each note... and crossfade between notes is programmed well enough (just listen to how VCOs glide, delicious) - which as you gather by now is a ton of work. So yeah there will be difference between digital oscs and analog oscs. Not as major as when it comes to filters.

For whatever reason virtual analog stuff just absolutely fails in capturing how analog filters behave. Sure there's stuff like Diva where the filter without the resonance sounds good enough - but the moment you add resonance - the gap becomes very noticeable. Analog filters will always have that air, brightness and crispness - whereas digital resonance will sound as if somebody just EQ-boosted the cutoff tip (which, ironically, is what resonance literally was made to do in the first place).

I have ESQ-1, it has noisy, 8 bit, single cycle waves - but those filters inside just make them all sound so full, soft and pleasant.

VCO all the way, get it right from the start.

For filters, CV via the Moog MF-101 filter is a beautiful thing with the MF-103 phaser - see my track "shooting star" for an example.

CV sources can modulate each other, and CV sources can be combined. CV can be easily adjusted, inverted, and stretched in any which way. Very fast. Not stepped.

The Analogue Solutions Oberkorn analog sequencer is my most influential piece of gear right now ... my biggest GAS at the moment is adding their Generator sequencer to my setup.

they have certain character of sound.

btw, many digital filters have their own distinct character too. but it's very different. (e.g. Z-Plane filters mentioned above)

P.S. i was very suspicious about „all that hype“ with analog sound until i bought my 1st analog synth.

The thing is, everything in the digital realm needs to be programmed by a person. Every subtle little thing results from code that was intentionally put there by a human. And as we all know, humans are very fallible. Things can be forgotten, unknown, or implemented poorly.

With analog, all the little quirks and nuances are provided for free by physics.

I love that answer. Just throw some sh1t on a breadboard and see what sticks.

For many analog synths, there's a saturation/drive stage before the filter, digital emulations of saturation/drive still tend to be unsatisfying (although they're improving pretty quickly). People underrate that saturation step IMO--for instance, a lot of the classic Minimoog sound is down to the way its mixer distorts.

Audio rate modulation is generally not as good digitally, since steps have to be taken to avoid aliasing (usually involving some band limiting). There's also this subtle analog "sizzle"/airiness around higher frequencies that I don't think any digital filters quite get.

The gap has been closing, but it's still there.

As time goes by I think this topic becomes less and less relevant. The oscillators in Legend sound very analog to me, in some ways more analog than my REV2. The filter in impOSCar 2 sounds more analog to me than the analog filter in my Peak. My point is that we’ve gotten pretty good at mimicking analog, and analog has often become so precise as to be able to mimic digital. Dogs and cats are living together, same sex marriage is legal and any fact you want to believe in is true if you find an Internet forum of people who believe it. In such perilous times, I recommend ignoring the tech and using your ears to choose things that sound good to you.

What no talk about the importance of keyboards?

I think you’re 100% right on that, but I’d also say that it’s also where a lot of modern analogs don’t do that well either. I think advances in electronics have made for internal dynamic ranges that don’t offer much up in terms of pleasing distortion. I was listening to a Prophet 5 r4 demo and in comparison to my 6, one thing I noticed straight off was that the 5 had this nice harmonic distortion where the 6 had this cleaner sound. In a sense, I liked the 6 more, but I wish there was a way to choose between the two different tones.

I'm quite a fan of digital oscs through analog filters. Especially 8 bit waveforms.

It is a very nice sequencer. You will be happy with it!

What was the synth?

Definitely not hype.

Try for yourself, however. Take no one's word...

DSI Tetra.

This is quite far from what i was expecting to read as an answer to his question.

There are hardware synths that still are very hard to match in software.
But Tetra ?
Hmm...

Tetra can sound really gritty (especially outputs 3 & 4).
and this is analog grit. totally different to digital synths.

It’s funny, I remember people saying that the Prophet 08 (which is the engine that the Tetra is built on, but with the addition of a sub osc and feedback) “sounded like a plugin.” At the time I didn’t think that much of it, but later I bought a MoPho (one Tetra voice) and one of the first things I did was put it up next to my favorite plugins. I sort of felt that Olga got the closest... but it didn’t get quite as good, especially in the grittier sounds that the MoPho could do using feedback and filter FM. Ultimately I liked the MoPho so much I got a Prophet 08 and now I have the REV2. If you think it can be easily imitated by a plugin, I’d love to know what one. The closest I’ve found so far it the Matrix 12 V, but it lacks a lot of the features of the hardware.

OK thanks, i'll do some research on YT.

It would depend on the patch.
REV2 is one of my favorite hardware synths too.
(just not favorite enough to actually buy it, haha)

Zero latency (well, almost) signal processing.

Can't one avoid latency with FPGA? the FPGA should be able to work literally on sample-by-sample basis, in the 10s of Mhz if need be.

I think the analog signal paths have bandwidth far below 10Mhz, the amplifiers alone must have quite low bandwidth, so there should be an equivalent latency baked in -- aside from lowpass filtering there's also phase delay from the imperfections of these amplifiers.

So 'computability delay' exists in a sense, in analog (the same kind that can mess up feedback loops)... just maybe at an order of magnitude more than the critically sampled audio rate.

It's probably possible to get pretty dang close. But it requires modeling of each stage.

A filter is not just something that attenuates frequencies so the resonance has to be modeled. So does the way it responds to an EG. And some filters are slower than others (LPG vs Minimoog for example). Many analog filters also allow driving the filter, which sounds harsh in the digital realm unless properly modeled. Then there's the signal to noise ratio difference. The extra noise affects the output whether you like it or not.

At some point, it doesn't seem worth the effort unless you're trying to design a VST.

Spot on. FPGAs can get to extremely low latencies. I hope to see more FPGA stuff around over time since the prices are dropping fast.

Of course, also spot on. Heck, even electo-mechanical devices like mics and speakers have a response time and speed of sound through air is a thing too. It all adds up.

I threw in a generalised, simplistic comment based on the current state of play for most of the products we currently see.

Because even if it's not the best sounding analog - it's still a good sounding analog.

My first synth was Matrix 1000 (the masochist's entry point... but I like programming synths damn it!) and even there the difference between virtual analog and analog was immediately apparent. That moment I've just stopped caring about emulation plugins. Things haven't changed still.

Or take JX8P for example. The analog filter in it is pretty terrible, it cannot do resonance. And yet it is still warmer than resonant virtual analog filters. In fact that synth is warmth itself - granted in no small part due to, oh boy, analog chorus (same as on Juno106 methinks) - another thing digital still can't do right.

i even can't recall where to find that kind of sounds on YT.
probably there are some, but definitely not much.

actually it was the lucky accident — i did not plan to buy any synths, but right before payday encountered Tetra for the price that was a steal, so decided to grab it. then did all research myself, recreating my favorite patches.

People seem to say Roland's Juno 106 emulation is spot on.

It isn't.

How so?