VACTROL!!

I do, I love a good vactrol jobbie. I have a few filters with them, too.

The trick is emulating that ping. You can do that with the slide~ object, among others. Set the slide_down parameter to match the discharge of the vactrol - it should still be very fast on the slide_up.

Perhaps one you'd like to add to the toolbox?

Great question! I'm curious about this too!

I hear that Aalto can do some vactrol-esque sounds. I'd be curious to see how they do it.

I bet you could get similar plucky, long-tail sounds with physical modeling but I don't know enough to really be of help.

You can fairly easily model the CV response of a vactrol as mentioned above but given the complexity of analog filters, I think there is room to explore a "vactrol-like" sound from a holistic perspective too, indirectly modeling that sound.

Thanks for getting back, everyone. Wetterberg, you are talking about... lowpass filtering (via slide~), e.g., an adsr~ and using that to modulate.... a filter cut off? Could you please tell me or show me what you mean when you say "that ping"?

Peter et al, I should have been more specific; I meant physical analog filters that use vactrols. Low Pass Gates, as they're called. I have some diy units and a MakeNoise QMMG, if you want to look them up.

And yes, it could be modelled holistically, but honestly, apart from doing resonance-squeals, the main attraction and difference between normal and optocoupler-controlled filters is the ping-sensation, which is just rubbery goodness all day long.

What I mean by the ping is that the cv control of a lowpass gate is done through the vactrol sections, and those have a slew to them; so if you feed it a quick pulse you get a fast-attack, slow release thing coming out, and that is what controls the filter. It is reminiscent of the things you hear in phys.modelling, but on traditional synthesis sounds it's really a thing to behold.
On top of that a true lowpass gate has both vca and vcf properties, so there's some tricky stuff in modelling that, too.

I personally believe that it could be modelled sufficiently with a control-addon to an already existing max/gen~ algorithm, but I'd have to do some testing - it's certainly an interesting area, that I'd love to help out with! A joint forum project, perhaps?

And don't forget a randomly chosen leakage amount...

absolutely... it adds punch. Or "vintageness", I forget which. ;)

So, I thought I'd post some sort of starting point for this forum project.... mhmm, Wetterberg:

p.s. Thanks for the filter model, Peter, it makes max a lot better sometimes.

You can actually still buy vtlc3s (the optoisolator in question) and the datasheet linked from this product page illustrates exactly the characteristic slew you're after: http://www.alliedelec.com/search/productdetail.aspx?sku=70219697

Would LOVE to see a good gen-based vactrol model. There's really not a heck of a lot going on under the hood of the actual Buchla LPG iirc (see for example http://www.dragonflyalley.com/images/BUCHLA292lowPassGate/buchla292-00-schematicB.jpg), so this would be a good, broadly useful, and (unless I am overlooking something massive) relatively simple starting point.